Good Parts, Anyone?

By Richard McCuistian

The ignition module on my own doggone truck crapped out in front of the wrong parts store...

 1980 F150 Explorer

79,986 miles

4.9L Engine

C6 Tranmission

“Got an ignition module for an ’80 model F150?”

Last 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'm teaching engine repair next semester and the 7.3L block might be a nice training aid, so I fired up my old pickup, left my subdivision, and headed up the boulevard.

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, but what the hey?  The truck had never put me down... until this morning.

I bought this old Ford for $2000 back in the summer of 1996. Since then, I've put about 12,000 miles on it. This 1980 F150 has about 80k miles total on it, so you can see that I almost never drive the old bomb. Don't get me wrong: I don’t ignore it completely: it has new tires and I recently replaced a leaking radiator with a new one. 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 the truck, I have to let the torque converter fill up before it'll move. That's how long it sits between drives.  People routinely ask me if the truck is for sale, probably because they think I'd sell it cheap because it spends so much time parked on the curb.

When I was replacing the radiator a couple of weeks back, I noticed that all the potting in the ignition module had liquefied 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 I knew when I saw it that my truck's 28-year-old Duraspark module was on its last wheeze. Be that as it may, in true form as wrench guy, I figured I'd take a chance on letting it show me what it had left. It would be a grand adventure, a calculated gamble. Since I'm the only driver, there'd be no danger of my wife or anybody else sitting beside the road due to my lassitude.  I did have plans to get a replacement module to toss behind the seat, but never got around to it.  Good intentions, that's all I had going for me.

Well, I 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 related to wet ignition parts.  The engine stalled.  I restarted it. It stalled again. I noticed that it would stay alive if I kept the ignition slightly past the “RUN” position, a maneuver that keeps the start circuit to the module hot without engaging the starter.  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.

     Jeep used Duraspark ignition on some of their platforms  in the late 1980’s to include the CJ, the 4 cylinder Cherokee, the gas-hogging Grand Wagoneer and the J-series full size pickups.  The Duraspark modules had different color grommets where the harness exits the module for different applications as the years went by; some modules had additional circuits for altitude modification and such, but the standard Duraspark module was a blue grommet unit. Other grommet colors on this box were yellow or brown, depending on the application. Ford’s EEC III vehicles in the very early eighties still used this module (albeit with a PCM and a crank sensor instead of a pickup coil).  Crown Vic police cars and taxis equipped with the 5.8L engine used Duraspark as late as 1991.  Ford’s Thick Film Ignition (TFI) replaced the Duraspark system on most Ford passenger cars beginning in 1984. Ranger got distributorless  ignition, a crankshaft mounted Hall Effect sensor that gave cam AND crank info, and a new module in 1989.  Explorer broke ground in 1991 with Electronic Distributorless Ignition (EDIS) that got its crankshaft speed and position information from a two-wire Variable Reluctance Sensor.

Limping to the Parts Store

As I kept toying with the ignition switch, I managed to limp on down the boulevard to the nearest auto parts chain store, 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.

The parts store carries a well-known line of aftermarket ignition parts (Wells), and the parts clerk sold me a peculiar looking little replacement module that had a completely different appearance from the OE part except for the bolt holes and the connectors. I opened the hood in the parking lot and plugged it in only to have the engine 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.

I reconnected my old module and the truck started right up.  I reconnected the new module and the truck snorted and kicked back again. It was the classic A-B-A swap that proved the N.E.W. (Never Ever Worked) part was indeed faulty.

Back inside the store (wearing jeans, boots, and a T-shirt, and not a one of my 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.  You're trying to use my parts to troubleshoot your truck.  We need to check your old module to make sure it's bad."

    "Why don't we check your new one?"  I asked. 

We did, using a handy dandy ignition module tester he had sitting on his counter top. The machine checked all the circuits and illuminated the red 'FAIL' light. The parts guy looked surprised, but I told him I wasn't surprised at all.  He got another new one and we plugged it in to the ignition module tester.  It passed with all green lights.

PICKUP COIL

One point of interest to me was that when I was working at independent repair shops, we replaced a lot of ignition modules on Ford cars, but when I went to work at the Ford dealership it seemed as if the pickup coil was almost always the guilty part. That seemed odd to me until I realized that most people had already tried a module, and when the module didn’t start the car, they reconnected their old module and called the tow truck.

Back in the parking lot, I tried the same A-B-A swap and got virtually the same results. If I hadn't seen this module pass the test on the machine, I would have believed it was the same part I had tried before.  Once again, the old module started the truck, and the new one acted exactly like the previous new module, green lights on the tester notwithstanding.

         Leaving the engine running with my old Ford Duraspark module connected, I walked back into the store to find the skeptical 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 and the engine died. I connected his new module and it wouldn't even start. I reconnected my original module and it started.

As the fat teeth on the reluctor go whipping past the wire-wound pickup coil magnet, the field shifts across the windings and a waveform is created that gives the ignition module speed and timing information.  Turning the distributor or moving the ‘breaker plate’ (a holdover term from contact points days) changes the timing of the waveform, thus the ignition timing is adjusted in that way. The module’s circuitry makes and breaks the ignition coil’s primary circuit in response to this wave, which produces the high voltage spark from the ignition coil’s secondary winding. That voltage travels through the coil wire to the center of the distributor rotor.  The rotor spins around under the distributor cap sorting out the spark and sending it to the right plug if the spark plug wires are in the right places.  This is an 8 cylinder distributor from the 302 in my dad’s 84 Ford pickup – notice that it has eight reluctor teeth. The one in my truck (4.9L) has 6 teeth.

"Doesn't that module have to be grounded?"  he asked. I groaned but knew how to answer his question.

    "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 machine.  It passed (again) with flying colors.  The parts guy was still skeptical.  This machine 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, and 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 from the other stores in town?"  I looked up at the big banner on his store 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 part was the wisest thing I could do."

    He gave me back my $23 and I drove down the street and bought a different brand of 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.

Without pointing fingers at any brand name brand or chain store, that's the F150 ignition module story.                 R.W.M.