I had a Code 42 condition in one of my 88 GTs (not the one that had the internal engine trouble recently).

I thought I'd share what it was for others that are having similar trouble.

I was getting an intermittent Code 42 that started as a rare condition that didn't seem to affect the car's driveability and slowly over a year or so got really bad where when it came on, the engine would run really poorly with no power.

Things I replaced:
- ignition module
- pickup coil
- ignition coil
- One of the ignition coil plastic connectors (one of the wires was slightly exposed at the top and I figured the wire might be bad inside)

No improvement.

I tried moving and repositioning the distributor wiring and inspected it by pulling back the plastic looms.

Finally I decided I had tried everything and maybe I need a new computer. Fortunately I had a spare computer. I tore the center console apart. I replaced the computer and no change.

Then as I was inspecting the computer harnesses and noticed I could pull one of the metal pin connectors out of the back of the connector. The plastic connector wasn't holding that metal pin in and the pin wasn't tight on the computer pin. I took a pair of pliers and clamped the connector slightly. Then I reinserted the plastic connector into the computer. BTW it was a ground wire pin not one of the wires going to the distributor from the computer.

The service engine light was gone when I started it up. Then I went back to the distributor. I repositioned the harness and the engine died. Started it up again and the Code 42 was back. Ugh so it wasn't the computer connector?

Then I put the harness back the way it had been. I closed up the console and drove the car for a few trips that way. Car ran great, no code 42. Went back to the distibutor wiring again and moved it around and the Code 42 was back.

I found a wire in the harness was shorting out. Fixed that and the Code 42 hasn't been back and the harness isn't sensitive to moving it around.

So there were 2 separate unrelated intermittent problems that were causing the intermittent 42. This is what made it even harder to diagnose. With just one problem it would have been much easier. So it was:

1) The computer pin was loose (just enough that car vibration was causing it to sometimes have contact an sometimes not) and
2) One of the wires near the distributor had a short (the short was intermittent in that it likely depended on how the loom was lying, temperature, moisture,etc).

Hope this helps someone else. This was the most frustrating diagnosis I've ever experienced.

Thank you so much for that.
I think many issues people have may be bad connections because of the age of the car.

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3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 03-10-2022).]

Awesome work. Glad you shared.

quote Originally posted by fierosound: Thank you so much for that. I think many issues people have may be bad connections because of the age of the car.

Yup the computer connector one was one I never would have thought to check. My typical troubleshooting would have unplugged the connectors, checked the connector pins for continuity to their wire end points, or replaced the computer, etc. So it was pure luck that I noticed that loose pin with the connector plugged in. Hope it helps someone.

I had the same problem a few weeks after I bought my 86 SE. No codes but the engine would just shut off while driving and then it would start back up after restarting. Took several hours to figure it out. I tugged on all wires around the distributor with engine running and no problem. I went to the computer end and tugged on the harness and the engine would hesitate. I used a pic or pen to wiggle each wire at the terminal clip and a white wire caused the engine to hesitate or shut off. I traced it back to the ICM in the distributor. No ignition = no run. I crimped the wire at the computer end and checked the others. I'm baffled as to what could of disturbed the wire in a secured place under the console.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

Sadly a "bad ground" causing DTC 42 isn't rare. Related are Ref and EST Wires between ICM and ECM often have same problems.

More the "bad ground" likely isn't a power ground that most think...
See my Cave, Ground "Myth" notes
IOW If the "Fake Ground" or the Reference wire(s) have problems you often get Code/DTC 42 "Electronic Spark Timing" to engine not running because ECM won't turn on fuel injection.

Worse the Exact "Fake ground" and other pins on ECM often changes for each version of ECM used for a given engine. Example: For Fiero...

code:

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Engine	"ground"	Ref 	EST
L4 Dist	Black 3 	Black 2	Black19	(Colors = plug color)
L4 DIS	Black 16	Black 9	White 6
V6 Dist	B3      	B5	B4	(I  think B section is latch side of Small plug)

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Note that 87-88 L4 DIS w/ DTC 42 can be problems w/ the PROM but you need to check the wires, pins, etc first.
Loose ECM pins like above is why this ECM plug version has pink "TPA" looks like a cover on the plug. All TPA are "backup" to stop pins backing out. (See my Cave, Terminal Access)

ECM has 1 or more "Real" Power Ground But Another Fake Ground is a Tan "Ground" bolted to the engine that is actually a Return Line from the "One Wire" O2 sensor.

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(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 03-13-2022).]