DIY PROMDo It Yourself PROM chip burning help. No PROM begging. No PROMs for sale. No commercial exchange. Not a referral service.
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I've tried all three ECMs that I have in my garage, multiple proms, multiple modules, checked the continuity on all my EFI harness wires (everything is less than 2 ohms). I also routed my plug wires very far away from the EFI harness (thinking I was getting discharges onto the harness).
Though I noticed that it always comes on after about 20 minutes of driving time.
Anyone have any idea what else I should be looking at??
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Knock sensor issue ??
Try jumping it with the right resistor to make the circuit happy and see if it goes away.
3.9K for the 350's, don't recall what it is for the 305 though.
I had code 42 on mine too, along with some other random codes (EST Error, Rich, and Lean, all at the same time).
I bought a re-manufactured ECM, or ECC (it says Electronic Contol Computer on the top of it-the new one) all codes are gone, and the Check Engine Light has yet to come back on (4 days on daily driving).
Hope this helps!
__________________ Cry at the pump, laugh at the stop light, thats how I roll.
1989 Trans Am GTA 350TPI 700R4
1978 El Camino 350/350
1993 Infiniti J30 Straight Stock (daily driver)
I've also seen Code 42 if the distributor timing is off a tooth, or severely advanced or retarded. Car Craft had a short article about it on the C4 Corvette this month.
Ido_marlins suggestion makes sense, though. An intermittant short would cause the problem.
305 and 350 TPI's use the same knock sensor, based on year. I know the 85-89's use one resistance value and the 90-92 use a different value. Sorry I dont know what the value is. Perhaps a search here will find it?
It's an EST Spark TIming Monitor Error.
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I've tried three different modules already. I can't imagine that every one of them has the same problem...
Last edited by ULTM8Z; 12-19-2006 at 10:55 AM.
Reason: Automerged Doublepost
EDIT well i just effed that up. that is more of a description of the code than the procedure. i can print out the flowchart if you need me to. i didnt read that closely enough. the flowchart should tell how to fix it
EDIT well i just effed that up. that is more of a description of the code than the procedure. i can print out the flowchart if you need me to. i didnt read that closely enough. the flowchart should tell how to fix it
Thanks. That was the same procedure that's in my AC Delco diagnostic manual. My car passes all of those electrical tests.
Wrong "grease" on the bottom of the module ?
Makes sense if heat builds up after driving for a while.
Just a thought.
You know what, I thought about that too. But I've been running dielectric grease under the module for the longest time and didn't have any issues with codes. I also did some searches on the internet and a few people said not to do that, but others say differently. I'm figuring if that was indeed the culprit, then untold thousands of people who use this stuff would be getting spark timing codes right along with me. Besides, I'm also running a ground strap from the module to the distributor base as well as a strap from the housing to the back of the cylinder head to ensure a good ground. The main battery ground is also connected to the cylinder head and my ohms check shows less than a half-ohm to ground when I probe my harness grounds. So I'm pretty darn certain I don't have grounding issues.
I would really check the ECM connector (on the harness) and the EST bypass if you still have one. It really sounds like one of them might be intermittent/corroded. Check the connection at the module as well.
The other thought is to check the ground wire from the module to the ecm. I suppose if its intermittent, it could cause some odd stray voltages.
So, that should be: the black/red wire to the distributor, and the tan/black for est bypass, and the white EST line.
if you can get the thing to generate a code, it might be good to check the signals by adding some probe points while it is running and monitor them. The best thing to use is a 'scope, however; that will tell you for sure if you are getting the signals back and forth.
if you can find the right connector (like the module), you could build a small harness that fits in between the dist and ecm, with pigtails for probes, this way you don't disturb the running harness.
wait a tick.....I just read your other thread and you are using a large cap distributor right? So....there is yet another connection inside the distributor for the module, check that one, and.....check the continuity of the wires as they pass through the grommet in the dist. body. Its certainly possible that the wire is partially broken passing through that grommet. Its like the issue (if you ever had it), of having a crappy set of headphones, that you had to wiggle the wires to get the sound to come out.
i talked to some other techs at work today and they said the Code 42 was a notorious problem with GM vehicles back in the day. they said it was a bad ground issue. you should check all your to grounds.
i tried printing the flow chart but it came out too small to read
i talked to some other techs at work today and they said the Code 42 was a notorious problem with GM vehicles back in the day. they said it was a bad ground issue. you should check all your to grounds.
i tried printing the flow chart but it came out too small to read
Hmmmm.... I guess I'll have to go back and check my grounds then.
On a hunch I would check the ESC process. Also make sure the temperature at $829C {edit: corrected location} is max'd out. That will disable the forced knock test.
I have a feeling that the code 42 is supposed to be a code 43, but is being reported incorrectly. I've seen several posts in the general/tech section where code 42's were fixed by items such as replacing the knock sensor. Shouldn't be that way.
Then the Car Craft article on the TPI Vette, a retarded distributor timing caused a code 42? Nope, shouldn't be. However, it will cause a forced knock test to fail.
On a hunch I would check the ESC process. Also make sure the temperature at $892C is max'd out. That will disable the forced knock test.
I have a feeling that the code 42 is supposed to be a code 43, but is being reported incorrectly. I've seen several posts in the general/tech section where code 42's were fixed by items such as replacing the knock sensor. Shouldn't be that way.
Then the Car Craft article on the TPI Vette, a retarded distributor timing casued a code 42? Nope, shouldn't be. However, it will cause a forced knock test to fail.
RBob.
Rbob, what is the parameter in Tunercat (if there is one) that corresponds to $892C?
If all I'm going to do is max out the temperature, I could simply turn the code 42 & 43 flags off in the switch table.
I suppose if the monitor error is only momentary then this wouldn't be a big deal. The car doesn't feel like it's running any differently after the light comes on. But I guess I don't want to simply mask a problem by "turning off" the error.
I'll have to check all of the above suggestions first.
With that GM module I put back into the distributor (reference a couple of posts above this one) I ran it on Saturday for a good hour and the 42 didn't appear. Though, I'm saying this with some trepidation rather than proclaiming it as SOLVED for fear of jynxing myself. I'm going to run it a few more times to see if the problem is really gone.
Now, the only problem with this particular module is that it's given me some no-starts before, which is why I haven't run it up until now. It's somewhat of a trial balloon to tell me whether I should go get another expensive GM module. If it no-starts again, even if it solves the code 42, I'll buy another one.
how old & what type of ignition coil do you have?
the reason i ask is because the coil can kill the module.
i will replace just the coil if the module is working ok, but if i replace the module, i always replace the coil.
if/when you know it is the module & you replace it, be sure you get the little package of grease with it, the GM modules almost always come with white thermal grease. dielectric grease works but it isn't the best, but its much better than nothing.
if nothing else, you can go to a computer store & get a tube of CPU thermal grease.
The coil is actually pretty new. Probably about 1.5 years old, which translates into maybe a couple thousand miles.
Yeah, I tried some of that CPU heat transfer compound. Problem is, the stuff just dried out over time and solidified (not sure if that's what its supposed to do). So I just switched back to the silicon dielectric grease.
Solved my problem....the memcal was not making contact within the ecm correctly sometimes. I just removed it and bent the ecm pins a bit and all is good now..no more code 42!!!
Congrats... Hopefully mine's gone too... 
