1995 Dodge Ram Pickup 4WD
Engine cranks normally but won’t start
Insurance Claims and Related Damage
My friend Steve was driving down the highway on his Nissan Quest a few years ago when a suicidal armadillo managed to waddle out of the weeds and knock the oil filter off his engine. That armadillo cost Steve’s insurance company no less than eight thousand dollars. Situations like the one Steve’s are why we as motorists pay insurance.
Back in 1985, another fellow we’ll call Bill managed to hit a muffler some previous vehicle had jettisoned onto the highway, and while it didn’t cost eight thousand dollars to straighten out his Eldorado, the repair bill was considerable. I had to replace his cracked transmission housing and reseal his engine (a diesel), which called for no small amount of labor on front wheel drive diesel Cadillac, but I failed to beat book time on the job, primarily because I wasn’t all that familiar with the product.
Caddys, Toyotas, and Peugots fairly regularly wind up at the Ford dealer for major work that would have been better (and more efficiently) done at their respective dealers and it has always stumped me. It’s not like we have better labor rates; indeed, our labor rates are higher than some of the other dealers.
At any rate, the Eldorado customer tried to claim that the impact of the muffler to his undercarriage had also damaged his power antenna somehow (never mind the fact that, if he was telling the truth, he wouldn’t have known about the inoperative antenna until after he got the car back) but I could tell from the dusty connector terminals that it had been unplugged for awhile, and based on my report, the adjustor rejected the argument that the power antenna had been working fine before the accident.
Caddy Bill’s attempt at tying related damage to an existing claim isn’t the exception, either. Lots of people want to get all they can for their insurance buck, but let’s be honest; insurance rates are already astronomical, and fleecing the insurance company won’t alleviate that concern.
Dead Dodge Truck
The body shop manager and I walked out to the body shop service lot behind the dealership.
It was a crisp, cold November day, the first real winter weather we’d seen since the previous March. Remember that; it’s important.
The body shop manager had first looked in vain for a fuel pump inertia switch, but Dodge doesn’t use one. When we spun the engine, the smell of hydrocarbons permeated the air around the truck. With the idea that the spark plugs may have been fouled by repeated cold starts and short run times (the wet spark plug syndrome is fairly common around body shops and used car lots where vehicles are started, only moved a few feet, and shut off), I pulled the ignition coil wire, stretched the spark and had the manager spin the engine with the accelerator held to the floor, a maneuver that puts the PCM in “clear flood” mode, effectively killing the injectors until the accelerator voltage drops below a certain level or engine rpm surpasses about 400 rpm. The incoming air, with no fuel injected, can and will sometimes dry the spark plugs enough so that the ignition spark will begin to jump the gap instead of taking the long way around the center electrode to find ground through wet soot, particularly with the increased voltage generated by the stretched spark.
With the spark stretched and the fuel injectors silent, the engine sputtered and tried to fire on some of the cylinders, something it hadn’t done with normal spark while spinning the engine with the accelerator released. Removing the spark plugs I found Bosch Platinums that were sooty and gas fouled.
“We’ll need to replace the spark plugs before we can go any further.” The body shop manager priced a set of spark plugs out to the insurance adjustor with the understanding that the problem might run deeper. Since the heavy 4WD Dodge would be so aggravating to push into the shop, I elected to do the work right where it sat.
Same Song, Second Verse
With a crisp new set of Champion OE spark plugs back in the holes, the starting problem persisted. I smelled as much gas and heard as much spinning as I had previously, and it took less that ten seconds to decide that all I had done was replace wet spark plugs with dry ones.
So much for the cold start/short run theory.
It was time to retrieve the scan tool and do some more checking. If I wasn’t sniffing so much gasoline while the engine was spinning, I would have elected to check the fuel pressure, but my gut instincts were telling me something else was wrong. My gut instincts were right.
The DRBIII is a powerful scan tool, bulkier than GM’s OTC Tech II or Ford’s Hickok NGS, but not quite so ponderous as the toaster-oven sized portable GenRad laptop scan tool Ford calls the Worldwide Diagnostic System. With the OBD I adapter plugged in under the hood and the key switched on, I waited for the DRB to determine which controller it was talking to, then punched my way through the menus to the DTC’s.
There were two trouble codes, one indicating an IAT voltage that was too high. The other code had been set by an O2 sensor that had apparently flatlined at some point.
Intake Air Temperature: How Important is It?
Early generation throttle body injected vehicles were notorious for running rich and fouling spark plugs due to an open Intake Air Temperature, or IAT (referred to as the Air Charge Temp on older Fords) sensor. Most of us have seen it on GM and Ford vehicles particularly. With an open IAT circuit, the PCM calculates the incoming air temperature at 40 below zero, and with that figure taken at face value, the PCM injects more fuel. The Engine Coolant Sensor was also prone to cause similar trouble if it was reading colder than the true temperature.
Oddly enough, the French programmers adopted a different IAT/fuel strategy on the Renault 1.4 and 1.7L Encore/Alliance platforms. 1987-1990 Jeeps were similar. A dead ECT sensor might not cause any noticeable driveability concern on those vehicles at all until the first cold snap of the year. At that point, a fair number of Renaults would come in on the hook for an ECT replacement. An open IAT sensor circuit on the Renault/Jeep line caused little more than a mild stumble on takeoff or tip-in; the “accelerator pump” function of the injectors having been calculated falsely by untruthful air density information.
Navigating the DRB III menu to the PID data, I found some interesting numbers. The Intake Air Temp sensor was reading 5.00 volts, and the smarter programming strategy adopted during the ‘90s dictated default of 104 degrees Fahrenheit. The wrinkle was that the ECT sensor was reading just above 40 degrees, a more accurate reflection of engine temperature, and on a cold engine with the hood closed, the Second Law of Thermodynamics dictates that ECT and IAT voltages should be exactly the same. The long term fuel trim reading was and adaptive factor PIDs were hung at 35%, obviously the reason for the gas smell and the fouled plugs.
This hard/no concern was a preexisting one; I could see that somebody had already replaced the IAT sensor with a shiny new part, but obviously to no avail. I was already envisioning an open circuit somewhere between the sensor and the PCM. During warmer weather, with the ECT voltage nearer the default value of the IAT, the engine probably started a lot easier.
It was time walk a hundred yards to retrieve a voltmeter. I was getting tired of taking long walks all the way from the rear service lot into the shop and back, but it was good exercise.
N.E.W. = “Never Ever Worked”
With a digital volt meter connected to the two sensor wires, I read a solid 5.0 volts, exonerating the wires leading to and from the PCM. A zero volt reading here would have sent me to the PCM for a continuity check of the Signal Return and IAT input wires, but now I could focus on the matter at hand.
Shorting the two terminals together generated a zero-volt signal on my scan tool IAT PID.
Switching the meter from DC volts to Ohms, I measured the resistance of the IAT sensor at the terminals and found the sensor open.
I had a life-size picture of somebody pulling up to a do-it-yourself parts house where a scan tool was connected, an IAT code was retrieved, and a sensor was replaced, only to have the same code return. I can hear the parts house guy saying:
“Sorry, it must not be the sensor. You’ll just have to take this one to a shop.”
Replacing one bad part with a bad new part can de-rail anybody’s diagnosis. That’s why it pays to check everything twice and don’t rely too heavily on DTCs and data streams. The datastream is at best a window into what the PCM is actually seeing and commanding, and at worst it can be a cloak for the real cause of the concern. DTCs can be equally confounding to a tech who doesn’t like to do pinpoint tests. That’s why the tool man still sells volt meters.
At this point, a Radio Shack 50K ohm potentiometer from comes in handy. Connecting the center terminal on the potentiometer to one IAT sensor wire and either one of the outside pot terminals to the other wire while watching the scan tool, I dialed in a temperature that closely matched the 41 degrees the ECT was reporting. The engine roared to life as soon as I turned the key.
(Side note: This little trick is also handy for checking the operation of radiator cooling fans. Watch the scan tool, paying particular attention to the radiator fan commanded state and the ECT voltage you’re controlling. If the PCM commands the fan on but the fan doesn’t run, it’s time to check the relay and related circuits. Just remember that on some vehicles, the engine must be running before the PCM will engage the fan.)
While this wasn’t a case of the customer trying to get something for nothing at his insurance company’s expense, he did get more than he bargained for while the rear end damage was being repaired.
And if the first cold snap hadn’t coincided with the body shop job and smoked out his hard/no start problem, we might not have even known he had the concern, other than the obvious Check Engine light.
As it is, I pass a lot of cars on the interstate at night with the MIL burning bright and steady, so he might have been ignoring the light for awhile, and getting approval for additional repairs on a body shop ticket can be dicey to say the least.
In the end, I told the body shop manager that the customer needed to return to the parts store where he got the original IAT sensor. If he still had the receipt, they’d probably be happy to provide him with another N.E.W. part that had Never Ever Worked.