Motor Age Garage: Good parts, anyone?

Jan. 1, 2020
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'm te

Even a lifelong technician isn't immune from vehicle repair at inopportune times.

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'm teaching an engine repair course 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 let me down — until that morning.

I bought this 1980 Ford F-150 for $2,000 in the summer of 1996. Since then, I've put about 12,000 miles on it, and it has only about 80,000 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 earlier, 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 a 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, those are 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 worked at the Ford dealership 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 Thick Film Ignition (TFI) modules work the same way. (See sidebar "Duraspark Popular on '80s Fords, Jeeps".)

As I kept toying with the ignition switch, I managed to limp down the boulevard to the nearest auto parts chain store, which isn't far from where I live. The truck was idling OK even in the "run" position by the time I pulled into the parts store 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 the module was the problem.

The parts store carries a well-known line of aftermarket ignition parts, and the parts clerk sold me a peculiar little replacement module that looked completely different 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 — none of my ASE patches) I encountered a skeptical parts guy who probably had seen a lot of DIYers trying to use his parts for troubleshooting.

"We don't need to just go swapping parts like this," he told me. "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 an ignition module tester he had sitting on his counter. 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. (See sidebar "Duraspark Popular on '80s Fords, Jeeps".)

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 said, as 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.

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

I told him it did not, and 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 still was 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 work in my truck.

"I don't know what this means," he said. "I mean, I've worked on cars for a long time. Ahhh, not professionally, you understand, but..."

"Look, I know what it means," I said, trying 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 20 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," he answered. "Do you think you can trust the parts from the other stores in town?"

"I don't actually trust any electronic part that doesn't come from the manufacturer," I explained. "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 drivability 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 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 its failed predecessor. My old Ford doesn't complain much.

Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. Richard is now an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, AL. E-mail Richard at [email protected]

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