87-90 Jeeps – A Breed of Their Own

In 1989, after my employing dealership bought the Jeep franchise, I spent a lot of time in Jeep/Renault school.  I was most familiar with the Ford engine control systems, and it seemed to me that the Renault/Jeep systems were a horse of a totally different color, and so I grappled with the oddities of it. In time, however, my perspective changed as I became more familiar with the product.  The 87-90 Cherokee/Comanche isn’t like anything else out there, and the fuel system on these babies is a peculiar study, so let’s take a quick look at it.

The fuel system is fed through 5/16 rubber hoses connected with worm clamps to steel lines from a pump in the tank that should hold its familiar 30-40 psi for awhile with the engine shut down.  If it doesn’t, pull the pump/sender assembly (you don’t have to pull the tank to do this) and tighten the hose clamps inside the tank. Voltage is fed to the pump through a ballast resistor from a relay over near the ignition coil and diagnostic connector.  There’s also a familiar fuel pressure regulator on the fuel rail.

By  the way, there are four relays in a line over there – The Fuel Pump Relay, the Power Latch Relay (which is controlled by one Engine Controller pin to feed power to another Engine Controller pin), the O2 Heater Relay, and the A/C relay.

The Cherokee/Comanche carries a multipoint sequential fuel system with a bell housing-mounted two wire VRS Crank Sensor (mounted on driver side at about10 o’clock), a distributor-mounted Hall Effect Cam Sensor for injector timing (50 percent duty cycle), an old GM style Manifold Absolute Pressure sensor, and Engine Coolant Temp sensor (up top and in the front) and an Intake Air Temp sensor (in the intake plenum behind the Throttle Body).  There’s an adjustable Throttle Position sensor on the Throttle Body that is a dual function unit on Auto Trans equipped platforms, so it has two GM style weatherpack connectors, each with three wires, and the connectors are discretely designed so as not to transpose.  

The Heated Oxygen Sensor looks like any other O2 sensor but is actually a titania unit that measures the temperature of the exhaust (cool is rich, hot is lean) and reads from 0 to 5 volts, with 5 volts lean and 0 volts rich, an arrangement that is antithetical to what we’re used to, but if you set up a scope and plot it on a graph, the pattern looks exactly like what you’re used to seeing, but remember, high O2 voltage reading indicates LEAN mixture, NOT RICH like everybody else’s system.  More about that later.

Notice that this titania sensor switches from 0-5 volts and when the voltage is high, the system is lean – when it’s low the system is rich -this is the opposite of a regular, more conventional sensor.

The Bendix Engine Controller is mounted under the dash above the accelerator pedal at a peculiar angle and it is simple to remove (if you know where the screws are) but irritating to reinstall because the screw holes aren’t easy to find.  That unit doesn’t generally need attention anyway, but be aware of it.  The 16 ohm injectors are hard-grounded and fired with voltage pulses from the Engine Controller rather than ground pulses like we’re used to seeing on everything else.

Idle speed is controlled with a GM style four wire stepper motor, but I sure wouldn’t try a GM Idle Air Control on a Jeep. We had a special tool for checking the operation of the stepper motor at the dealer, but I have no idea where you could get one now. One set of windings in the IAC is connected to terminals A and B, and the other is connected to B and C.  Make sure you compare the cone-shaped pintle on the end of the old one and the new one if you have to replace it… there are a couple of different pintle shapes used and the aftermarket people tend to foul this up sometimes.

The Throttle Body has an idle stop screw, but don’t jack around with that one.  The idle air bleed screw is on the side of the Throttle Body behind an aluminum plug, and I haven’t seen one in recent years that hasn’t been tinkered with, but if it hasn’t been tinkered with, leave it alone.  Cleaning the Throttle Body and IAC bypass passage is very easy to do on this engine and should be done at every oil change.

The PCV system consists of a grommet in the rear of the valve cover with a ¼ inch vacuum line connected to it.  The grommet has a small hole that meters the vacuum.  With the closure hose disconnected from the air cleaner and capped with your thumb, you should feel a slight vacuum with the engine running.  If you feel pressure there and see crankcase steam, you’ll also have oil in the breather: Check the PCV grommet for clogging as well as the vacuum line and the hose nipple to which it connects.


The ignition system is beautiful in its design, with an e-core coil tidily mounted right on an ignition module that takes its orders from the Engine Controller.  To check the operation of the ignition module and coil, just disconnect the two-wire weatherpack unit, connect your test light to power, and touch the probe to terminal B of the ignition module. The coil should fire each time you tap the terminal.  The scope pattern it produces is unique, so get used to what a good one looks like.

The crank sensor that provides engine speed and crank position should read at least 480 millivolts  AC while the engine is spinning with the starter, and if it doesn’t the Engine Controller might not respond to the signal. The connector is at the rear of the intake plenum, usually with a red wire and a white one. Measure this voltage with:  A. The crank sensor disconnected,  B. A cold engine, C. Your Digital Meter on 2000 mv, and D. Somebody spinning the engine.  If the voltage is nonexistent, replace the sensor.  If it’s a bit low, use a long screwdriver and gently bump it closer to the pulse ring. The crank pulse ring is a study in and of itself.

On Auto Trans 4.0L Units, it has a lot of small windows separated from each other by very narrow metal vanes.  At 120 degree intervals throughout the circle, it has a wide window and a wide vane.  When it sees a wide window and vane, it knows that a cylinder is 90 degrees before TDC, and it uses the sync signal from the Cam Sensor in the distributor to determine which cylinder is coming up.  If the sync signal fails (and sometimes it does), then the Engine Controller will simply pick a cylinder at random on startup, and on some starts it might run better than others.  If something bends just one of the thin vanes inward, the Engine Controller will be confused and won’t fire the coil in time.

This is the cam sensor pattern

The spark plugs are easily accessible with the exception of #1, and the firing order is the familiar old straight six 1-5-3-6-2-4. A distributor sorts out the spark the old fashioned way, but the timing is not adjustable, primarily because the Hall Effect unit in the distributor has nothing to do with ignition.  Put the distributor in with the rotor just passing the #1 firing post when the timing mark is on zero.  Don’t, and you may have a road speed surge due to rotor alignment/timing advance issues.

With a cutout cap and the crank on Zero TDC (compression stroke), you can use a cutout cap like this one to turn the distributor so that the rotor tip is just past the #1 post – that puts the post in the center of the firing window where it should be.

One looming difficulty is the fact that the Bendix system’s datastream is totally inaccessible if you don’t have a Chrysler DRB II with a special adapter and cartridge, and to my knowledge, the aftermarket folks have never addressed the need.  There is no Check Engine (MIL) light, and the orange Emission warning light that comes on after a certain amount of run time is tied to a special clock box under the dash that is dedicated to that purpose.  The clock is resettable to kill the light if you know how to do it, but I won’t go into that here for lack of space.

There is no way to retrieve any trouble codes (which are worthless on this one anyway), and determining fuel trim numbers is a faraway dream without a scan tool.   The diagnostic connector on the Cherokee/Comanche platform consists of two separate plugs mounted in a stamped steel plate over on the passenger side of the engine compartment near the Ignition Coil/Module assembly.

The old MS1700 Renault tester we initially used would work, but it was so slow, squirrelly and clunky as to be non-usable. Be that as it may, there are multiplied thousands of these old vehicles (the giant majority are 4.0L) still running the road, and there are some ways you can track down problems on this generation, so if you’ve been buffaloed by some old Cherokees (pun intended, but it’s a stretch), maybe this article will be a good addition to your files.

If you have a transmission that won’t shift, check this fuse – it feeds the Transmission Control Unit, which is mounted right under the glove box. A Cherokee will shift manually if this fuse is blown but it won’t shift automatically.

First off, measure all the voltages on a properly running Cherokee or Comanche as soon as you can. This takes some creativity, but the sensors aren’t hard to find, and as technicians we have to be creative by our very nature, right?.  You need to know what the sensors are reading with the engine running and not running, cold and hot. Those numbers will be your guide.  Connect your o-scope to the ignition system on a good one and note the peculiar shape of the waveform – take a digital photo of it or store it if you can for future comparison.

One of the most common driveability problems is stalling, and if cleaning the throttle body and IAC passage doesn’t fix it, try having a look at the O2 sensor:

The one wrinkle here is that if the Oxygen sensor intermittently fails at low voltage (and it generally does), then an ECU in closed loop mode will attempt to correct to the lean side and cause the engine to stall. Remember, on these, low voltage is interpreted as RICH, not lean. The O2 sensor heater is fired by a relay in a small bank of four over near the ignition coil and the diagnostic connector. So how do you find it if the sensor reads normally in the shop and you don’t have a DRBIII, connect a Digital Multimeter and drive it until the stalling occurs.  Ideally, the customer may have noticed a pattern that you can follow to duplicate it.  If the O2 voltage plummeted to the basement and stayed there shortly before the stall it generally means the O2 sensor is at fault, and sometimes the threads come out with the sensor, so be ready with your 18mm spark plug tap.

As with any system, the key to fixing this one is to get to know it.                           R.W.M.


The 66 Bug, My Dad, and Patty

My dad ran a VW repair shop for a lot of years, and while he probably drove and owned literally hundreds of beetles during his 30 year career, one of his favorite and most trusted cars was a 66 VW Bug he practically built from the ground up and drove for a long time. In its early life, it was primed red, and he used it for his work car – since he ran a one-man shop, he’d have to hang a note and close the door before he went to town.

For a long time, before he obtained a replacement transaxle, the car would jump out of fourth gear, and so he drilled a small socket in the gear shift knob and used a stiff piece of welding rod propped between the knob and the dash to keep that 4th gear jumpout from happening – you see, my dad was a pragmatist and he always thought outside the box – in that case, I guess you might say he thought outside the gearbox.

As for me, pumped 40 cent a gallon gas, did brakes, built carburetors, fixed flats, and read Louis L’Amour westerns during the slow times at the only Gulf station in the very small rural community where we lived. When Ed, the mechanic who ran the gas station for Clyde, his silver-haired father, moved to the Texas coast to work in the offshore services business (oil was a whopping $13 a barrel then), he coaxed me a few months later into following him down there.

I worked that job for a few years, and after I married, and shortly after Jimmy Carter de-regulated the petroleum industry in a failed attempt to fix runaway inflation and correctly predicted that gas would go from 40 cents a gallon to a dollar, I found myself needing a gas-saving ride, and so my dad sold me that 66 bug, now painted a color something between pale yellow and pastel green.

In the meantime, governmental Imminent Domain claimed my dad’s shop property in the waning years of Carter’s presidency because that highway was being four-laned, and so Dad built his new shop with the small amount of money they paid him for his property. Rather than buying a prohibitively expensive piece of land in town, he put the new shop on an acre of land next to our house out into the country without so much as erecting a sign. His notion was that since he had so many regular customers, they could find him if they wanted to. And they did.

As this was happening, I was still wrenching on my fleet maintenance job down on the coast some six hundred miles to the west, and under the carport at my Texas residence (a house on Lakeshore Drive that I had purchased for $16,000) sat the 66 bug – it was one of our family vehicles along with a 74 Ford pickup and a 79 Chrysler Lebaron, and when I moved back to Alabama with a wife and 2 kids, the bug came with us.

Well, at the point when we moved back to Alabama, my dad’s shop was temporarily closed – he was in Tennessee learning about sawmills with plans to set up one of his own out behind the shop to supplement his income during those times when car work was slow. After he got his sawmill set up and running, I built a four bedroom house with oak lumber we sawed out of eight trailer truck loads of logs, and except for the decking, every board in that house was sawed out on the mill he set up.

During the time he was in Tennessee gathering experience and information about sawmill stuff, I was the one-man operator of his shop, and I serviced vehicles for his regular customers and more or less kept things flowing, but I gathered some new customers too, and one of those is a principal player in this story. Patty was a single mother with three kids whose soldier husband had dumped her, and she had purchased a 70 model tan-colored bug from a rather shady used car dealer in a nearby hamlet that was known for its small town politics and speed trap-happy cops.

While the car looked good inside and out, it was fraught with one problem after another. The first time I worked on it, I changed the oil, cleaned the oil screen, and adjusted the valves – something those old bugs need very frequently. Incidentally, VW bug maintenance calls for an oil change every fifteen hundred miles.

On the day I first worked on Patty’s car at that shop in the country, I noticed two things – first, it was raining, and second, she had disappeared. As I was finishing my service on her bug, I realized she was approaching from the open doors on the other end of the shop.

“What happened to you?” I asked. She was soaking wet.

“I just went for a walk in the woods,” she replied with a peace-joy-love hippie type smile. This was a strange, sad little lady.
Over the next month or two, she would call me for first one thing and then another that went wrong with her bug. Once she called from the bus station telling me there was something wrong with one of her wheels and she couldn’t drive the car. When I got there, the pinch nut that holds the wheel bearings in place had backed off and her wheel was wobbling like a cartoon when the car moved.

Another time the spring broke on the points in her distributor, and then another time the fan belt broke (who knows why, it didn’t look that bad), which led to an engine that got hot enough to take the temper out of all the piston rings. I jerked the engine out and stuffed a new set of rings and three new quarts of oil in there to get it going again, hoping the bottom end hadn’t been damaged by that debacle – that didn’t take but about two hours and the car ran like new.

This one repair after another mess led her to become so disgusted with that car that her hippie smile disappeared one day and she voiced her frustration. I just about had all the kinks worked out of her ride, but she still didn’t trust it.

“The 66 VW I drive doesn’t give any trouble, and I just put a brand new extractor exhaust system on it. Wanna trade?”

“Will that 66 bug make it to the beach?”

“I drove it all the way here from Texas and I drive it all the time around here.”

“Even trade?” She asked.

“You got it.” I told her. The car she was driving was a lot more comfortable than the 66 and was 3 years newer. Further, it had a good looking paint job. For cars of that vintage, no title was needed in Alabama, and so we simply swapped bills of sale.
The 70 model bug was, by design, quieter and more comfortable than its four year older predecessor, and I drove it for a year before I sold it. All the kinks and problems had been worked out of it while Patty still owned it, but a vehicle can quickly lose the trust of a single mother if it puts her down too often, and this car had done that.

Patty still brought the 66 bug back to me for service whenever it needed work, and she was has happy as a bug in a rug driving that one, because it never broke down.

Right before Dad came back from Tennessee, the guy I had worked for at the Gulf station asked if I would like to work for him – he had built a new shop and had more work than he could do, and so, about a week before my dad made his re-entrance, I closed his shop again and went to work for my previous employer. Dad re-opened his shop and started taking in work again. I told him the story of the 66 and 70 bugs, and he grumbled good naturedly that I had traded the good car he had built for a “piece of junk.” We laughed together about it and moved on, but we both got another laugh about the situation later on, and it happened on this wise.

One night after we were off work, Dad and I were standing in the shadows of the big pines out by his shop when he told me Patty had driven up that day on the 66 bug, and asked where I was. He told her he was my dad and that the shop was actually his shop and that I was working at another shop.

“Well, I won’t let anybody touch this car except Richard.”

My Dad isn’t often surprised by much of anything, but when that girl wouldn’t let him put a wrench on the car that he built because she didn’t trust anybody but me – well, he was surprised and disgruntled, but was kind of proud of me at the same time. And as he told me about that encounter, the laugh we shared about that car and that girl’s perspective was particularly memorable.


He got his sawmill up and running, and we sawed out 40 thousand board feet of lumber to build a house with four bedrooms, two bathrooms, a grand room with exposed beams, and a shady porch on the front and back. It’s said that three things every man should do are to plant a tree, build a house, and have a son. I’ve done all three, and my dad has too.

He doesn’t work on cars much anymore, except to tinker with the vehicles he and my mother drive. If anything major needs doing, he brings it to my shop at the school. A few weeks back he brought his Tempo to me because it wouldn’t idle down, and in addition to replacing his Idle Air Control valve, I was using swivel head ratchet to replace the spark plugs.

“Remember that Snap-On swivel head ratchet I gave you ‘way back in the eighties? I paid $27 for that ratchet and two spark plug sockets in 1977 and I always hated it because the head was so easy to strip I bet the Snap-On guy rebuilt it a dozen times.”

“I still have it,” he replied.

“Yep,” I smiled “and I reckon I’ll get it back after you’re gone.” We shared one of those special father-son moments and had another good laugh. We never know when any of us will pass from this life into the next, but both my parents are full of days and have blessed a lot of people in the years they’ve lived. And by God’s grace, I’ll bless at least as many people as they have.

Tires More than 6 Years Old Are Unsafe

This was as student of mine who thought his tires were just fine because they had good tread. They did look good but they were outdated. Tires more than six years old are unsafe, even if they have been stored in an air conditioned warehouse. Don’t let this happen to you.


Parts House Adventure

One Friday morning I left the house on my way to Dothan, the big town down the road where I worked for so many years – the Ford dealership parts manager had a brand new 7.3L engine block he needed to dump, either on me or in the scrap iron bin.  I fired up my old pickup and headed up the street.  I’m teaching engine repair next semester and the 7.3L block might be a nice training aid.

The weather was kind of damp and misty, and the old truck tends to skip and carry on in weather like that; it needs a set of wires and a cap, but I’ve been putting that purchase off for years, dreadfully guilty of my own indictments to others about ignoring known concerns.

I bought this truck for $2000 back in the summer of 1996. Since then, I’ve put about 12,000 miles on it. This 80 model F150 has about 80k miles total on it; I almost never drive the old bomb, but it has new tires and I recently replaced the radiator due to a leak. This is the vehicle I leave at the airport when I fly and at the school when I’m on a road trip in one of the college vehicles.  When I start it, I have to let the torque converter fill up before it’ll move. That’s how long it sits between drives.

When I was replacing the radiator, I noticed that all the potting in the ignition module had liquified and trickled out of the box to re-congeal in waxy rivulets on the inner fender.  I don’t know why that happens, but I’ve seen it before.  And with that in mind, I knew that Duraspark module was on its last legs, but I figured I’d take a chance on letting it show me what it had left.  Since I’m the only driver, it was a calculated risk – no danger of my wife or anybody else but myself sitting beside the road due to my lassitude.  I did plan to get a replacement module to toss behind the seat, but never got around to it…

Well, wasn’t even at the end of my street before I realized I had big trouble.  The truck popped and skipped in a peculiar way that I knew wasn’t wet ignition part-related.  The engine stalled.  I restarted it. It stalled again. Only I noticed that it would run if I kept the ignition slightly past the run position, a maneuver that keeps the start circuit to the module hot.  That circuit uses a different part of the ignition controller and it wasn’t uncommon when I was at Ford to find that a car would run on the start side of the module but that the run side had failed. The small gray module-mounted TFI modules work the same way.

As I kept tinkering with it and restarting the truck, I managed to limp on down to AutoZone, which isn’t far from where I live.  The truck was idling okay even in the run position by the time I pulled into the Zone parking lot, but I wasn’t going to chance a 60 mile round trip with that used-up module under the hood, and I knew good and well the module was the problem.

Auto Zone carries a line of ignition parts called “Duralast,” and the parts clerk told me this line of parts used to be WELLS, but I can’t verify that, not even doing internet research.  Maybe it’s WELLS’ second line?  I don’t know.


I bought a peculiar-looking little replacement module and plugged it in right there in front of the store only to have the truck kick back and carry on like it had crossed spark plug wires or something. I checked the cap for moisture and didn’t find any.

Reconnected my old module – the truck started right up.  Reconnected the Never Ever Worked module.  The truck snorted and kicked back.

It was the classic A-B-A swap.

Back inside the store (wearing jeans, boots, and a T-shirt, no ASE patches) I encountered a skeptical parts guy who had probably seen a lot of yo-yos trying to use his parts for troubleshooting.

“We don’t need to just go swapping parts like this.  We can check your old module to make sure it’s bad.”

“Why don’t we check your new one?”  I asked.

We did.  The Wells machine checked all the circuits and illuminated the red ‘fail’ light.

The parts guy looked surprised.  I told him I wasn’t surprised at all.  He got a new one and we checked it on the WELLS ignition module tester.  It passed with all green lights.


Back in the parking lot, I plugged the second new module in with the same results.  Same A-B-A swap. The old module started the truck. The new one acted EXACTLY like the previous new module, green lights notwithstanding.

Leaving the engine running with my old Duraspark module connected, I walked back into the store to find the parts guy.

“Can you come out here for a minute?”  I asked.

“Sure,” he was more than courteous.

The engine was running.  I disconnected the module.  The engine died.  I connected his module.  It wouldn’t start.  I reconnected my original module.  It started.

“Doesn’t that module have to be grounded?”  I groaned.  Okay, here we go.

“No.”  I told him.   “It doesn’t.”  I fingered the harness.  “See this black wire?  That wire comes from a terminal screwed to the body of the distributor and that’s the only ground this module needs.”  The orange and purple wires go to the pickup coil.  The green wire goes to the ignition coil.  The black wire that is grounded in the distributor provides the ground that the module uses to fire the coil.  The red and white wires are the start and run circuits. There is NO external ground necessary on this box”

He was shaking his head, a little shocked that I knew the system that well, but he remained unconvinced.  After all, how much can a guy in faded jeans and a T shirt know anyway?

We retested the module on the WELLS machine.  It passed (again) with flying colors.  The parts guy was still skeptical.  This WELLS diagnoser was his go-no-go tester.  Yet in the last five minutes he had seen one module fail and another one pass on the machine, yet neither module would start the truck.

“I don’t know what this means…” he muttered,  “I mean, I’ve worked on cars for a long time… ahhh… not professionally, you understand, but…”

“Look, I know what it means.” I tried to be gentlemanly.  “It means this machine can’t be trusted.  It doesn’t load the internal module circuits the way the module is loaded when it’s firing an ignition coil.  It can pass a module with all green lights and the module can still fail to work right.  If I had driven twenty miles to get this part instead of being right outside the store I’d be pretty hot. Wouldn’t you be?  The acid test of whether these modules are good or not is out there, not in here, green lights or no green lights.”

“Well, I just need to refund your money, I guess, and let you go somewhere else.  Do you think you can trust the parts at O-Reilly’s or Advance?”  I looked up at the big AutoZone banner for a second or two. At the risk, of sounding like Mitch Schneider, how could I answer that?  Let me count the ways.

“I don’t actually trust any electronic part that doesn’t come from the manufacturer – when I was at the Ford dealer, I don’t know how many times I replaced aftermarket ignition parts to take care of annoying misfires and the like. If I saw an aftermarket ignition part on a car with ignition-related driveability problems I found that replacing it with an OEM was the wisest thing I could do.”

He gave me back my $23 and I drove down to Advance, where I bought a Sorensen ignition module that worked like a brand new one. I went and picked up the 7.3L block.

Oh, and by the way, I just plugged it in and let it lay on the fender.  When I have time to bolt it down, I will.  Until then, it can ride next to it’s failed predecessor.  My old Ford doesn’t complain much.

That’s the F150 ignition module story.

Don’t Get Burned

Be careful around a hot engine – even if you’re smart enough NOT to open the filler when the hoses are tight, hoses with pressure can still burst without warning – 3rd degree burns will ruin your whole day.

I noticed this swollen hose on a 1997 Pontiac and backed away really fast – this one was running nice and toasty at over 200 degrees, and if that hose had burst and sprayed coolant my way – well, finish the thought.

Diagnosing hard start complaints

When I first picked up wrenches and started trying to get a handle on how cars worked, it was fairly simple to figure out why an engine wouldn’t start. We’d first check for spark and the proper firing order, then we’d yank the air cleaner, prop the choke open (if it was working right it’d be closed on a cold engine) and we’d operate the throttle to watch the accelerator pump jets. From there, we’d jerk the spark plugs out and see if they were wet and sooty or used up.

Hard starting diagnoses typically led down a slightly different path, and because we’re talking about newer vehicles, we’ll fast-forward a bit and mostly try to leave the carburetors and oil-filled coils in the past.

Spark First

For years, contemporary wisdom in textbooks and some older shop manuals said to let the spark jump ¼ inch, and if you had that much spark, it was enough. Working with my dad as a youngster, I discovered the biggest problem with that ¼-inch rule was that a spark can jump that far in sea-level air pressure and still not have enough of a pop in the chamber to light off the mix under compression.

The spark needs to be downright scary these days, with enough blue-white (not orange) energy to punch through nearly an inch of air and pop loud enough to be heard three service bays away. I’ve seen some really good technicians stumble over that ¼-inch spark test and then call for the “calf rope” because they had been side-tracked by weak coils that wouldn’t produce sufficient spark.

So how did they get off track? Well, the spark would traverse that ¼ inch and they didn’t stretch it to see when it reached its limit, so they erroneously figured they had eliminated spark and in error they moved away from the ignition system with their troubleshooting.

I remember one hard starting 1988 Taurus that would actually fire up after spinning for 30 seconds or so, and it had me stymied until I connected the ignition O-scope and found that the coil was incapable of producing the voltage needed and it would jump only about 1/2 inch.

That was acceptable on older oil-filled coil systems, but on the Taurus I was troubleshooting, it wasn’t enough. A new coil took care of that one.

So when testing for spark, make sure you stretch that blue lightning far enough to determine that it’s not weak. That’s rule No. 1 on a single-coil vehicle with a hard start concern.

As far as coil packs go on Distributorless Ignition Systems, single towers or whole coils on multi-coil packs can stop delivering spark and Coil-On-Plug (COP) coils can drop offline for one reason or another. But weak spark generally isn’t the cause for a hard-start on coil pack or COP equipped platforms.

Then there was the Bronco that would start only with the SPOUT connector disconnected. I found that problem with the Service Bay Diagnostic System. The PCM ground traces would go crazy while the engine was spinning, and that turned out to be a voltage drop problem at the battery cable-to-engine block connection.

There were the burned-through rotors and faulty ignition modules, but they’re more likely to cause sputtering and stumbling than hard starting.

Understanding Fuel Delivery

With spark either verified or eliminated as a possible cause, the next thing we need to know about our no-start is how much battery voltage is still available to the PCM with the starter doing its thing. Most systems won’t operate the injectors if the available voltage drops below a certain level.

Fords typically won’t start if the system voltage goes below about 7.5 volts, and the engine will seem to be spinning at a pretty good speed, but it won’t even try to fire up (this is also true on Power Stroke Diesels).

If the system voltage is sufficient, it’s important to know whether or not the injectors are clicking and what their pulse width is in milliseconds (ms). You can do that with a scope or an enhanced scan tool datastream. Remember, however, that the datastream isn’t giving you real-world information like a scope — it’s simply giving you a window into what the PCM is trying to do and usually updates pretty slowly. You’re really getting the information filtered through two computers on the way to your eyeballs.

Let’s think of fuel delivery at startup in a simplistic way: Tecumseh lawn mower engines have that funky rubber thumb pump to wet their tiny manifolds. On carbureted engines, before the engine will start there has to be a surplus of fuel in the intake manifold, thus the accelerator pump and the follow-up of the closed choke.

Fuel injected engines are no different when it comes to required fuel. During start, particularly cold start, the injectors either fire simultaneously or bank fire so as to provide the fuel needed to light the engine off in lower temps. And moving the throttle while you’re spinning the engine can put too much fuel in there (it adds additional pulses to simulate the carburetor’s accelerator pump delivery), so watch for in-range TP sensor failures that might cause hard starting or rich running problems.

Furthermore, it is quite important for the Idle Air Control (IAC) to be wide open during initial start for that no touch starting feature we’re all used to. If it doesn’t provide the needed air (because of sticking or whatever), a bit of throttle opening typically gets the mill fired up. But as an old-timer, I have to remind myself that there is a whole generation of customers warming car seats nowadays who have never had to touch the throttle to start a vehicle, so you can’t expect them to do it instinctively if the IAC valve sticks.

Spark plugs get really wet when there isn’t any air to go with the rich fuel supply provided during the cold spin, and wet spark plugs don’t fire because the voltage follows the path of least resistance. That’s called flooding, and it can wash down cylinder walls in a flash.

A Throttle Position Sensor (TP) that is drifting into the Wide Open Throttle range with no throttle movement can cause intermittent hard starting concerns because most fuel injection engines shut the injectors down at Wide Open Throttle.

Dripping injectors can cause hard starting as well. As a matter of fact, one dripping injector can flood an engine all by itself (I’ve seen it several times), even if it isn’t dripping all that much.

That gasoline steam that fills the plenum tends to condense on spark plug tips when air starts to flow.

Typically, a hard start due to an injector drip will show up hot, and the engine will spin for a bit (sometimes 30 seconds or more) before it starts and it might run rough until the wet burns off the spark plugs. Spin it until the moment it fires up and then shut it off immediately. Pull all the spark plugs out. The sooty or wet ones will be the ones with the dripping injectors. If the injector tips on those same cylinders are washed clean (they should be dirty) then you have found your leaking injectors. I’ve used that trick for years.


The Stubborn Altima

Let’s take a peek at a special case I ran into recently. It helps to understand the principles outlined above, and our experience with this Altima hard start problem will illustrate that need.

A woman called me about her daughter’s 1997 Nissan Altima. It had been at a local repair shop for a few weeks and they finally gave up on it. She told me the car had a history of minor fender benders (all in the front end), and she wondered if that might have anything to do with the problem she was having. The crash info was pertinent information, to be sure, but would it turn out to be significant? I’d have to factor it in if need be.

She asked me to call the shop where the car was languishing and speak to the technician who had been working on it, and so I did. The tech’s remarks were somewhat interesting and provided another clue.


“It’s really hard to start cold,” he told me. “But you can spray some carburetor cleaner in the manifold and it’ll start right up and run just fine for the rest of the day. There aren’t any stored codes, but I believe there’s something going on with the injectors. I temporarily plugged in a used PCM but it didn’t change anything.”


Did you pick up on that important piece of data? He could add fuel and it would start normally. What did that mean? As mentioned previously, TP sensors can fail in range (drifting voltages with no throttle movement) and cause that kind of anomaly, but even with the TP sensor near the WOT range and the PCM in Clear Flood mode, the engine will start if the rpm goes above 400.

In the service bay with diagnostic weapons hot, I fired my first salvo.

Spark: Hot and bright, even during the hard start.

Spark timing: Dead on the money, even during the hard start.

OBDII Scan tool: No codes, no glaring discrepancies in the datastream.

Fuel Pressure: Normal (40 psi off and 30 psi running) with no leak-down at shutdown.

Battery Voltage With Starter Engaged: 10.9 volts and holding steady.

After the Altima sat fallow for a few hours, the Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) readings were about 10 degrees apart. That got my attention until I realized that the 10-degree spread might have been due to the fact that the heaters work so well in our shop. The IAT was the warmer of the two sensors, and it was between the inlet and the air cleaner where ambient air could reach it.

I keyed on the temp sensors because I had worked on a Dodge pickup that flooded the spark plugs and simply wouldn’t start at all on a cool day. It turned out that the IAT sensor was completely open and the PCM had substituted 110 degrees, which wasn’t such a big deal if the coolant was nearer the reported (substituted) air temp.

What was even stranger was that the IAT sensor had just been replaced. Incidentally, the OBDII datastream won’t show the substituted value; it shows -40 degrees. Rule of thumb: All the temp sensors should read the same after a thorough cold soak.

Back to the Altima. With the scope connected to an injector line, I measured about 10 ms pulse while the engine was spinning and not starting (you could run the battery down spinning this one and it wouldn’t start unless you released the key and tried it again), and about 3 ms pulse after the engine finally fired up. Without another Altima for comparison, I didn’t see much wrong with those numbers.

I thought about it. I slept on it. I reflected on the Altima’s wiring schematic and the fact that there is a dedicated start signal wire from the ignition switch to the PCM, and that there is a fuse in that circuit. If the PCM doesn’t know the key is in the Start position, it won’t know it’s supposed to double pulse the injectors. If that was the case, it was firing the nozzles sequentially and not wetting the manifold sufficiently to fire the engine up cold.

Another piece of evidence that supported the improper fuel delivery was rooted in the fact that I saw very little needle pulse on the fuel pressure gauge with the engine spinning (usually the needle bounces pretty good during start).

Based on my hunches, we measured start signal voltage at PCM pin 20 with the key in the START position. There was no voltage. We searched for the location of the suspect fuse in ALLDATA, then discovered that it was fuse 23 and it was plainly labeled on the instrument panel fuse block cover as Start Signal. But there was no fuse in that slot. We installed one, and the hard start problem was gone. It was as simple as that.

Interestingly, the literature we had on hand didn’t mention that as a possibility. It simply took a basic understanding of gasoline fuel systems to make the connection. The owner paid our basic charge and bought a fuse.

A Change in Perspective

Once I traveled to a nearby town with a fellow instructor in an attempt to recruit some high school students from that school in that town. He and I taught different disciplines, but we were recruiting for our entire division.  He was a passionate, vociferous gentleman of great dignity and really enjoyed presenting before groups of students.

Every group of students has a different personality, as peculiar as that might sound to those who don’t teach.  And one group of boys looked like they were so totally disinterested in everything. Their eyes were on their desks, or looking around at others, and their faces were masks of utter boredom.  I stepped forward and put my hand on my colleague’s shoulder to pause his presentation.

He is a well-muscled, broad-shouldered man with big hands who shaves his head and dresses like a CEO when he’s not teaching his technical trade.  He paused with a pained expression on his face – not so much because I asked him to give me a moment as he was that they weren’t hearing anything he had to say about his program or technical education. He stepped back with his big, callused hands clasped in front of him while I addressed the group.

“How many of you boys know about that ‘tough man’ contest the comes around every so often where guys sign up for a ten-thousand-dollar prize if they can beat every other guy in the contest one-on-one?”  All their hands shot up. I pointed at my fellow instructor. “He entered that contest and won that ten thousand dollars.”  I stepped back and motioned for my fellow instructor to continue.

From that point on, their eyes were on him. That one tidbit totally changed their perspective and from what we could tell, they heard every single word he said for the rest of his presentation.

Stuck on Stupid

Three jobs where almost nothing went right but we won the fight anyway.

We run through quite a bit of work, and the ones we really learn from are the hardest ones to figure out. We also learn from our mistakes, and yes, I know I’m the only one who ever makes a mistake (NOT).  Students sometimes disassemble things they didn’t need to because of inexperience, and other times they’ll have to backtrack because of some important part that was left out during assembly.  Then there are those times they’ll approach a big or complicated job without even looking at the shop manual, and they’ll put themselves in a bind.

For one example among many, I had a guy replacing the engine in a 2005 Kia Sportage a few years ago, and he just plowed into it without doing any reading at all. Well, when he got the engine disconnected from the transaxle, he discovered that there wasn’t enough room to get the engine out of there without bringing the transaxle with it.  Had he simply perused the information system verbiage before beginning that task, it would have gone a lot smoother.

He could have looked at this single image and had a lot easier time of it – as it was, he tried to pull the engine out from the top and there wasn’t enough space to separate it from the manual transmission after he got all the bolts out.

Then there are times when following the shop manual is a really bad idea because some of the information in the shop manual is SOS, i.e., “Stuck On Stupid,” as if the procedures were written by a desk-bound service engineer who never actually laid eyes on the vehicle.  Surely I’m not the only one who has ever run afoul of such misinformation! We did work on a Kia Sedona that provides a perfect example of the misinformation malady, meaning we would have been better off NOT to have even checked the shop manual R&R procedures.

SOS Number 1

The Sedona came to me from a family member who had noticed compressor noise that was so bad he couldn’t stand to operate the A/C unless it was really hot outside. The A/C was cooling just fine, but that noisy compressor needed to be gone, and so I put a couple of my people to work on it. We’d replace the compressor, the drier, and the expansion valve.  Knowing the Asian penchant for stuffing the expansion valve in the evaporator case, I wasn’t surprised to read in Alldata that the evaporator case needed to be removed in order to replace this TXV, and when we took those published procedures for gospel, we made a wrong turn. Most shop manual publishers get their information from the manufacturer’s shop manuals (with permission), but some of the Asian manuals leave a lot to be desired, and this one was no exception.

The shop manual said to remove the dash and pictured the expansion valve inside the plenum (see drawing) but the valve was actually in the engine compartment.

In strict obedience to the Alldata service procedure on this platform, they removed the instrument panel, which, by the way, on one of these Sedonas, is no small feat if you haven’t done one. I usually stay out of the way when it seems like my folks are making progress and following procedure, but as I walked by this van about the time they got the panel out, I mentioned the fact that those “block” type expansion valves are usually just inside the engine compartment rather than in the evaporator case (except on Toyotas), and that’s when I peered into the dark recesses of the engine compartment on the passenger side and found that this van was no exception to that rule of domestic normalcy. The entire dash removal was totally unnecessary, because the valve was right there where it was supposed to be. Oh, well. They needed to jank a dash and put it back anyway. So be it.  The end of the story was that the dash went back in well and the compressor is now cool and quiet.

SOS Number Two

The second SOS job we’ll peruse is a cute but intrinsically boring little 2007 Cobalt. The first time we saw this one, it was running awful.  The girl who drives it is a gentle soul who wouldn’t speak a harsh word to or about anybody, but in this case, she had good cause to complain, but she told her story with a smile.  She had gone to a shop in a nearby town a few days earlier to have them look at the car because it was running so poorly at idle, and she said the shop replaced the spark plugs (that’s all they put on the bill) and charged her $500, but the car still ran like a three-legged dog. Well, when she asked why the bill was so high, their reply was that half of it was labor. She didn’t even ask why the car still ran so poorly, she just drove away and came to us. She was “Stuck On Sweet.”  Too sweet, if you ask me!

What my guy found was a sizeable split in a hose, and when he fixed that vacuum leak, the little car idled smoothly, but when we drove it, the right front wheel bearing was quite literally so loud it sounded like a two cycle engine running at wide open throttle in the right front floorboard while you were driving along.  The owner didn’t even mention that totally off-the-charts bearing noise, and if the shop that replaced those very expensive spark plugs had done a verify-the-repair test drive they would certainly have heard it.  We got the green light to replace that right front bearing and after we did, the Cobalt drove like a little piece of heaven compared to what she had been experiencing before.

About three weeks later, she called me again and said she had run over something in the road she thought was a stick, only it turned out to be a piece of rebar that created a massive breach in that aluminum oil pan, and all the engine’s slippery juice found its way onto the highway in very short order.  She indicated that she hadn’t driven it far after the impact, but when we got the oil pan off, it turned out that one of the rods had been hot enough to change color – it was deathly gray.

Never a good sign – this bearing got red hot for lack of lube.

The local chain parts store is typically pretty good about getting replacement powertrain components through LKQ. I used to deal directly with the local LKQ depot, but it has moved. So I had them price me out a replacement engine, and the owner gave the go-ahead.  My guys got the engine out of the Cobalt with the powertrain lift, then they rolled it over to the area where we do our disassembly/reassembly and they disconnected the engine from the sub frame and the transaxle, then removed it and put it on an old tire while the new engine was headed our way. That’s where the SOS syndrome kicked in at the parts store.

Two weeks went by – the engine should have already arrived.  I called every day to ask about the ETA, and my industrial sales parts guy kept saying he was expecting it “any day.”  Well, it turned out that the LKQ truck had dropped it off at the parts store when the industrial sales guy was absent, then another truck came in with pallet-loads of parts, and the second-string crew stacked a bunch of pallets in front of the engine, which had been shoved against the wall.  It sat there for ten days before anybody figured out what happened.

When the engine arrived, we pulled the flywheel off to check the rear main seal and removed the valve cover to check for sludge.  The rear seal was seeping, but the innards of the power plant were sludge-free. They popped the seal out and we ordered a replacement. When it arrived, one of the guys came carrying the new seal holding it up next to the old seal he had picked up from the table and it was obviously a different size.

Now WE were in SOS mode, only we didn’t know it. I called the parts guy, thinking the engine we had received was a newer model or something, because there were other differences that had to be addressed between the old and new engines and other parts that needed transferring.  The parts guy was bewildered, and when our personal cloud of SOS smoke cleared, we discovered that my guys had picked up a rear main seal we had replaced from a 91 F150 for comparison to the replacement seal and that the first seal had been the right one all along.  We lost another day or two sorting that nonsense out.

We finally got the Cobalt back together (we installed the other shop’s $250 set of spark plugs in the replacement engine for good measure), filled it up with oil and coolant and watched the ECT with the EASE Wireless Vehicle Interface while the thermostat opened and closed and the fan cycled, test drove it a few times, and she was back on the road.


SOS Number Three

This one was one part SOS and one part ground breaking experience, which is never a good combination but always interesting. The car was an ancient 1997 Mazda 626 V6 that was featured in a previous article – they had dragged it out of a barn and we had cleaned the fuel tank and replaced the fuel pump to get it going.  Later we had replaced a weak ignition coil because it was sputtering and misfiring under load. They drove it for a year or two and then it started making some funky rattling noises and they wanted that checked.

My substitute was running the shop while I was at KC Vision, and the students just knew they needed to remove the engine oil pan, which was totally unnecessary, but the sub let them do it.  In the process of checking the bottom end, one of the guys managed to do the not-too-smart SOS thing and turn the engine backwards, which caused it to jump a few timing belt teeth.  I figured this out when I returned, because there was a big half-inch drive ratchet hanging on the crank bolt and it was set to turn the engine counter-clockwise.

I had them yank the timing cover to check the marks, and sure enough, the engine was out of time. But while we were there, we discovered the reason for that rattling noise, which I recognized, but they didn’t.  That self-contained hydraulic timing belt tensioner was all squishy and needed replacing. Well, we replaced the tensioner, and put a timing belt kit on it along with a water pump, and we put a set of serpentine belts on as well, reinstalled the oil pan, and poured in new oil with a new filter and new coolant in the jacket.

We got it running without a rattle, but it had an annoying misfire, and when we investigated that, we found a split plug wire insulator and most of the spark plug wells nearly full of engine oil. The customer wanted that fixed too, and so the intake was removed, the valve cover gaskets, spark plugs, and wires were replaced, and since the starter tended to click a few times before it would spin most of the time, the starter was replaced as well at the customer’s request.  This bill was climbing really fast on a car that might be worth 500 bucks sitting by the road with a for sale sign on it.

Well, that’s when SOS kicked in again. The car wouldn’t start after the work was done, and the guy working on it said he couldn’t hear the injectors but that it had fuel pressure – long story short (too late), the O-scope showed injector pulse, so he had taken a wrong turn thinking the injectors weren’t operating.  After the guys all left one day, I found that he had mixed up the banks when installing the plug wires, and I fixed that to get it started, but the starter was spinning so slowly it would barely crank the engine, and so we got it off and I bench tested it to find it spinning very slowly and with great effort.

A second replacement starter was sent, and it was bench tested as well – it spun aggressively and powerfully in the vise, and so we installed it, but on the car, it would spin slower than normal, even with good strong battery power.  A voltage drop test showed some ground-side loss, and so we replaced the ground side cable, connecting it directly to the upper starter bolt, but the starter still spun slower than normal.

This was getting weird. Sometimes the starter wouldn’t spin at all, and during one of those times, my guy used a low-impedance test light to check for power at the solenoid terminal with it disconnected from its spade and got really good power. What the heck was going on here?  SOS, I figured.

There was voltage drop between the positive battery terminal and the starter solenoid wire – thus even when the solenoid would engage, it wouldn’t happen with any force – and that caused voltage drop INSIDE the solenoid, which delivered low voltage to the starter – which fried the starter after a few attempts to start the vehicle.

I took my pocket screwdriver and shorted the starter’s hot terminal to the solenoid spade and the starter spun like brand new – the conclusion of this matter was that the ignition switch was dropping enough voltage with current flowing to the solenoid so that the solenoid windings weren’t getting enough current to jerk that big copper washer against the internal contacts.  That test light that burned brightly was a deceptive test, because it doesn’t pull as many amps as the solenoid.  A meter and a high impedance test light are pretty useless in situations like this too.  Best to use a headlight bulb to check for adequate amperage.

I was going to demonstrate this to some of the other guys so they’d get a better understanding of voltage drop and what it means, but when I did the pocket screwdriver thing that copper washer welded itself to the contacts inside the solenoid and the starter wouldn’t stop spinning until I removed the battery cable.  The solenoid’s washer needs to pop hard against its contacts like a hybrid vehicle system’s battery contactors, and it had been compromised by not smacking the contacts hard enough too many times. We had to install yet another starter and an ignition switch to finish the job.

Doing one right…

A Buick Rendezvous that had been to two other shops that had given up on it for no fuel pump operation and no-start, we found this:

This terminal leaves the underhood fuse panel to carry power to the fuel pump and it was scorched – this wasn’t the first time this Buick had given this problem – previously, somebody had replaced that one terminal (see right) but we replaced the entire fuse panel with a salvage yard unit and fixed it for good. Finally we got one right.

The end of the story is that, like the vehicles we have to work on, we don’t always operate at our full potential. Further, we’re all human, and sometimes things come at us so fast that we make snap decisions, taking things at face value, and draw false conclusions that lead to wrong turns. But we don’t have to stay Stuck On Stupid, even if we’re having a bad day. And as I tell my guys and gals, any time you get so sick of a car that you want it gone worse than you want it fixed right, you’re out of touch with what it means to be a good technician. We can stay in the fight, fix it right, and win if we will. R.W.M.

A Tailgater

This car followed me for about 15 miles on a long straight piece of road at 60 mph – could have passed me safely a dozen times. The driver looked like a teenage girl. I could have tapped the brakes and she would have smacked my back bumper.