jerrspud

1987 car. I fixed the code 33, and then the code 34 that came up after I replaced the MAF. Now I'm on my last code and it's a 42.
I'm going through the trouble shooting tree and I just want to make sure I'm doing this right and why it doesn't make sense to me.

So it says to "prob the ECM harness conector ckt 423". I was testing the wire in the dist, but I just realized... it's talking about the ECM wire under the dash right? So I need to unplug D4 and test that? So that test will see if the wire (423) is good and if the ignition module is good because you do the test with the ignition on. Am I on the right track?

thanx

jerrspud

so yes... It needs to be tested on the ECM end. Now.. I'm pretty sure it's the white wire on on the larger left harness. It has a number 4 on the inside of the ecm and that matched a white wire. Now... do I leave both of these unplugged for the test? Should I only unplug the grey one? Do I pull the white wire out of the harness and plug the rest in?

There is little info on this test. I'm I the only one that has had this problem?

thanx
Jerr

Cliff Harris

Error code 42 means that the link between the ECM and the ICM is open. That is usually because the EST connector is opened to set the base timing. The ECM sets code 42 when you do that. Just reset the computer and the problem will be gone.

Triple Black 88

I had a code 42 on my 88 last week and it ended up being the ECU itself. I replaced it and it fixed the problem.

Kevova

Code 42 is a PITA especially when it's intermittent. There really is no clear cause; Ignition module, ECM, wiring with this application timing connector, poor connections, poor grounds or emf. The cheap stuff make sure ecm grounds are clean and tight with silver colored (cadnium)nuts, make sure timing and 4 wire connectors locking tabs are intact and terminals aren't damaged, route plug wires at least 1 inch away from the 4 wire EST harness. and make sure distributor hold down is grounding distributor. Grease under ignition module and mounting bolts not rusted. After the cheap stuff it's a guess between ignition module and ECM. Ignition module endures more heat cycling so I would try it before an ecm

jerrspud

thanx Cliff. I did check that and it was closed. Took a while just to figure out what that was, what it was for, and were it was.

I think that may be all it is. I just ordered one for $20, but I still want to do the trouble shooting test just in case it's the wire.

The code is always on and come on right after code is cleared. I think I'm just going to ohm that white wire to make sure it's good between the dizzy and the ECM. If that's good, It's probably the ignition module. I'm still really curious on the correct way to do the step 2 test. I may try it over the weekend again.

The plug wire routing has come up a few times in my research on this. I'm guessing it's noise I need to worry about, but what is the correct plug routing? Where is that "4 wire EST harness"? The wires are a bit of a mess and not on the harness clips

thanx guys. I have three other GM vehicles, but this is my first Vette..so I got some stuff to learn.

Cliff Harris

The 4 wire harness comes out the back of the distributor. There originally was a plastic insulator for this harness but it always breaks from the heat. The insulator is part of the harness, so you can't buy one -- and of course the harness is no longer available. Here's what to look for:

jerrspud

that's some awesome info. I did break that darn grommet thing last week and was looking for one. Now I know why I couldn't find one. :-(

Tod Stiles

I know this is a little OT but this is the way I fixed the broken grommet problem. I cleaned the whole area with some brake clean and then used a piece of painters tape across the opening. I got the wires centered in there, sort of forming the tape around them. I filled the area with black silicone and let it harden overnight. Took the tape off, trimmed with a razor where the cap goes. I'll be darned but it came out looking pretty good for something no one will see.

Cliff Harris

I've been planning to do this but haven't gotten there yet.

jerrspud

so the adventure continues.

I did the ohm test at it seemed to be around 5K. No were close to 500 ohms. I ohm'd the white wire (423) and it looked good. So it has to be the module.

I ordered a new one but it was an aftermarket one. This time the test was even worse. Now it's 10K. My only guess is that this is a bad module as well (it was a Borg Warner CBE15 from Ebay). I ordered a new GM one from RockAuto to see if it is truly the problem.

If it's not the module, maybe it's not getting power? The test is run with the ignition in the on position. The troubleshooting does not cover anything about if it is getting power. Does anyone know what wire supplies the Ignition Module with power?

Cliff Harris

It's the pink wire that goes in the side of the distributor cap. Some people call it red, but it's definitely pink. This wire comes from the ignition switch.

You can test for power on the module by lifting the distributor cap and probing the ignition module power pin (red wire). The pink wire needs to be plugged in and the ignition on.

jerrspud

that's good to know....thanx. I'll check that. I'm surprised that's not part of the test. That would be funny if that's my problem.

jerrspud

ok.. progress is made.. but not much good news.

With a new GM module the test seemed to work.

Ignition on both cables removed from ECM
-D4 wire had less than 500 ohms CHECK (result was 222ohms)
-D5 wire light test. No light. So it passes (not grounded)

-D4 ohm test with light plunged into D5. Ohms jumped up to over 5000 ohms as expected. (result was somewhere around 10K)

All this means Ignition Module was good.

Put everything back together and now the code was gone. Drove car around block and check engine light came back on. Code 42 once again.

Ran all the tests again and Ignition Module was still passing. That means it's now the ECM. My guess is the heater in the car heated it up and it failed?

I'll retest it after the car sits for a bit to confirm the findings.

Rock Auto is around $100 for the ECM, but I need to swap the chip. It that easy to do? I hope it comes with instructions.

jerrspud

Well the troubleshooting chart was spot on.
I replaced the ECM and all codes are now clear.

thanx for the clarification to my questions.

Now that it has run a but, it's idling too low now and stalls. So on to the next problem