So, this may be a long read, so bare with me please. First I am new to the forum. Hello everyone, I am glad to be here! So, a family member of mine has a 1990 Camaro Iroc Z with a 305 tpi in it. The car runs and drives, but has electrical gremlins in it. For starters, it has a persistent code 42. Let me go through what I have did. So, the car came to me and wouldn't flash any codes, even though the service engine light was on. I took it to a shop that works on these cars and race cars. He hooked his computer to it and it said failure to connect. Puzzled, I took the ecm out and seen someone had installed a hypertech chip on the prom. I took that out and plugged the prom back in and it then flashed code 42. So, I went into investigation mode. I took the 3 connectors off the ecm and unplugged the 4 pin connector off of the distributor icm and ohmed across for continuity. All wires checked good in the harness. So, I assumed a bad icm. I did a full tune up and dropped in an entire new distributor and coil from Dan Block performance and new wires and plugs. I verified that my bypass circuit connector on the passenger fender was plugged back in after setting my timing and all that. Anyways, code 42 was gone and it ran like a scared jack rabbit...until the next morning. Code was back and it ran like garbage. It will intermittently go off and run good and then just randomly come on and run like crap. I have crawled over every square inch of the wiring. I even went so far as to take apart the connectors at the ecm and distributor and bend the connection points down a fraction so that they bite down on the pins better...I though maybe a pin connection was loose. Another problem/weird thing is that the idle air control valve will stick wide open for no reason, hot or cold. It works normal sometimes, but randomly changes. I also checked every square inch of the IAC circuit and changed the IAC 3 times as well as changed its connector. Same story. The car will literally run like a scolded butt ape one day, then you can turn it off and not touch anything and the next day everything is going haywire. The only stored code is 42. Which is intermittent. It has had people fiddle around with every square inch of the car too. It had a MSD box installed on it as well. I took it off because the part numbers didn't even match the correct one for the car. It showed to be for an old carburated car. They had did a bunch of hacked up wiring and splicing and crap that I had to repair. They had harbor freight butt connectors all over the ignition system with no heat shrink and it was a mess. Anyways, I have checked the wiring a hundred times and its all good and nicely fixed now. I have looked at schematics and about wore the probes out on my voltmeter checking this darn thing. Someone also installed edelbrock performance intake and plenum on it and took the factory air cleaner system off and put some janky little tiny cone filter on it. I am going to fix that back better later, after I get it to run right. So, anyways, at this point, I am leaning towards it being an ecm problem. I have changed/repaired everything else. What do you guys think? Should I try a new ecm?
Oh, someone has also installed aftermarket electric fans and rather than do it right, they just hot wired them into the key on ignition so that they run continuously when the key is on. I need to fix that too, but I don't see that being related to this problem. They have a aftermarket aluminum radiator in it too. It is like some kid tried to make a race car out of it and really hacked it together. I keep finding messed up stuff. It is overwhelming me if I am being honest.
edit-I also forgot to mention that the ecm has 2 fuses?? Maybe...I found a wire with a fuse holder by the battery. It had a 20 amp fuse in it. I didn't see it on my schematic, so I pulled the fuse and the ecm went dead. Is that a factory wire? Because it also has a second fuse for the ecm in the fuse box. I thought it may have been a fuel pump fuse, but when it killed the ecm, that threw me for a loop and left me scratching my head. Oh, and I need to edit again, I keep remembering more stuff. Sorry. I also found that the little plate above the throttle blades, with the 4 screws, has nothing under it. From what I researched, that should have components in it that open and close for the pcv system...right? Anyways, someone gutted it out for some reason. Maybe more flow? I don't know. Anyways, would that be why the idle air control valve isn't working right?

 

This is a bad indication, a random/intermittent wiring issue it would appear, but where? It's either the ignition control circuit, specifically a random short or a bad/loose/corroded ground between the Power Control Module (PCM) and the Ignition Control Module (ICM) would be my guess based on face value. It could be the PCM for sure and you may also want to check the knock sensor circuit, it can cause this condition as well. I wish you GL.

 

C7 is the est bypass on the 1227730 ecm

 

is there a code 43 ?
I missed that

 

Sorry, no. The OP did not mention that. However, I have seen some very odd things in the past with CFI which was related, so I thought I would at least mention it just to ensure there wasn't something else involved. I hope that did not distract from the original issue. Like the diagram, nice!

 

Thanks for all the great responses so far. I thought it could be a bad ground as well. I checked the ecm ground circuits in the harness as well as the icm ground wire in the harness. Ohmed to ground, they show to be good. I tried wiggling the harness and wires with it running to try and replicate the fault. It made no difference. As for the knock sensor, it's wire was messed up and the insulation missing in spots. I think I repaired that now. I didn't see any more bare spots. Short of taking the entire engine harness out and laying it on the ground, I have looked it over pretty good. Could I take the ground wire off the ICM and jump it straight to ground without hurting anything I wonder? ... in other words, not ground it through the ecm?
I will double check the ecm grounds again. According to the schematic I have, there is 4 ground wires on it. I will ohm them to ground and see if they are good. I did that once already, but maybe I missed something. I will also run through the steps listed for checking the bypass circuit that was posted above. I didn't have that guideline and just checked end to end for continuity, which checked good. The ICM is good/new. I changed it with 2 other ones to make sure. 1 was off of my own 89 chevy. It was a good running one. So, I know it was good. The ICM and ignition circuits should be good I think, but I will run through the test procedures listed above to confirm. Thanks!

 

Here is my diagram I am using for reference. It is for a 1990 305 iroc. It matches the wire colors and seems right for the car. Let me know if you think it's wrong in any way. I got it from an online manual. It seems right though.

 

I appreciate the info! I did notice 1 discrepancy in your pictures. On the first picture, you show the ignition coil as having a ground and a wire to the distributor on the secondary circuit. Mine don't have that. It just has the 4 wires on it. Is there supposed to be 2 additional wires on the coil body??

 

Are you referring to the body of the distributor being grounded per schematic?

 

yeah, my coil only had 5 wires. On the 2 connectors on top. A ko ignition feed, tach, power feed to dist, and a white signal wire to dist, and the spark wire to the cap. Is there supposed to be 1 more?

 

think you need your glasses adjusted only 4 wires on this schematic on the coil

 

Yeah, but it shows a ground? Is that just a reference to a ground through the body of the coil? Sorry if I was being dense and misread it. I am reading all this during green skies and a tornado warning. I am in Oklahoma where the wind gets pretty rowdy. I was standing at the back door with sirens blaring. I relooked at it and it all makes sense but the ground. Just wanted to make sure I didn't miss something.

 

Learn how to read a schematic, yes reference that the body is ground

 

I had a random 42 code and it ended up being the ground located at the (2) screws that hold the ICM to the dizzy base plate. They were rusted to the point of bad connection. Removed the ICM, cleaned up the base plate, applied some fresh heat sync paste, wire wheeled the screws really well and cleaned the ICM ground sleeves and reinstalled.

I suspect you have some wiring issues with the sounds of the hack job you've been handed.

Best of luck!

 

No need to throw stones here bud, I assumed that, but didn't want to just assume anything. I wanted to be thorough. What are the 2 metal brackets for with the coil kit? Do they serve a grounding function? The old coil didn't have them installed, so I left them off. Could that be an issue? It had a bracket with 2 bolt through it on the bottom of the coil. The 2 in this pic...

 

Not throwing stones, the picture above is clear. The only difference is this is for a 1227165 you have a 1227730 . The pinout attached for icm to ecm inputs.

 

Ok, I do have the right schematic for the car I believe. I uploaded it in one of my post above if you want to take a look. Its in a different format. Its from Chilton. Tell me if it's not, because that's what I have been using. It seems to cross pretty well though. It has the proper pinout locations and everything.

 

Stick to helm information, way more accurate

 

Where do these 2 brackets go? They came with my coil and I would like to install them right. I don't think thats the problem, but I like to be thorough and do things right. Otherwise, it bugs me. What are they for?

 

Helm? OK, does it require a subscription? I have a tech subscription through Chilton already. I haven't heard of helm. I will look into it.
This is the link to my subscription. It's different than their manuals. It's more in depth.
https://link.gale.com/apps/CHLL?userGroupName=down54663&authScheme=

 

Is helm an acronym for Haynes electronic manuals or something like that? I don't use Haynes, but anyways, I can't find helm on google.
I actually may have finally found it. I searched Helm automotive manuals and it had a link that sent me to a page that said E manuals in the header. I searched for the car and it brought up a good manual looked like. It wanted me to pay though, but let me preview some of it. It looked pretty good. Is that what you were talking about?

 

Grounding straps for the coil

 

Use this it’s from a 90-92 fsm

 

Ok, that's what I thought. I was wondering how they are supposed to install on the coil. My subscription info through Chilton doesn't mention them at all. That is also why I asked about your schematic and if it was supposed to have a ground wire attach to these straps. Sorry if I was being vague. I was trying to ask about these straps from the beginning. How do they ground the coil if nothing connects to them? There are 2 holes in each strap, but the holes don't line up with the coil holes. It's almost like wires with eyelet connectors are supposed to bolt up to them? Or am I being an idiot and just not figuring out how they go on? Thanks for your patience and help. I know you must be getting frustrated. Sorry

 

@Tuned Performance Thanks for all your help and advice. You know alot about these cars, whereas I am still learning them. You helped tremendously. I am going to use your information and test the est bypass circuit. That should tell me once and for all if it's an ecm problem. As for those stupid little ground straps. I spent the last hour or two pouring over info and other forums...turns out the general consensus is that they are for other applications. They said that the coil is used across multiple applications and that it's fine to not use them. So, I guess I won't. Anyways, thanks for your time and advice!
Others are welcome to add their info as well. I will take all the knowledge I can get on these. I need it!

 

So, I just did all the steps provided by Tuned Performance. I ohmed the white est wire with key on. 223 ohms, which was good. I then put 12v test light on bypass wire. It did not illumunate. Which test good. I then put 12v power to bypass while testing ohms on est. It went to 5750 ohms. Which test good. The final part said to start and see if light illuminates. It did. It then said faulty ecm. So, it's a bad ecm.

 

What brand ecm should I buy would be my next question. Should I just go with a reman GM genuine or a cheaper brand? It looks like there is Cardone and GM genuine is the 2 that offers them for the car with the right part number. I would assume GM is better, but that's just an assumption. I know Cardone makes crappy stuff for other models. Here I'd what I was going to get probably...unless you guys say otherwise.

 

Cardone can be hit or miss , acdelco ECMS 1227730 , 16196344 , 16198262 are all interchangeable for the 730 ecm. Might just look at rerun policy before purchasing to insure it will function.

 

Helm's service manuals are the ONLY manuals you should be using to troubleshoot your car. Helm is the provider of all the major car manufacturer service and wiring diagram manuals. If you have a fireplace, use Chilton and the others for a fire starter, they suck IMO. If anything, you may get them on eBay and save some cash. HELM MANUALS

 

Thanks for posting a link. I appreciate that! I browsed through some of them. They look nice, but I didn't see where they offer a tech subscription...they might, but I didn't see it. I work on multiple vehicles (mostly diesels) and need a subscription that covers all makes and models and offers labor estimating and sps subscription capabilities (for GM). I have multiple subscriptions, but use the Gale Chilton subscription for labor estimating and tech procedures. It's not like the Chilton manuals you buy in a store, it covers all makes and models and is for technicians, not DIYers. I will say that they suck on older vehicles though, but are very in depth for anything mid 2000s and newer. Anyways, HELM looks nice, but may not work for me. I am not arguing though, for these cars, you guys have WAY more info than I do with that subscription. If I owned the car, or worked on them all the time, then I would definitely purchase their manual.

 

Hey guys, I just wanted to update this thread and post the results of the ecm replacement. I purchased the ac delco ecm and installed it yesterday. The code 42 is gone and the IAC valve is functioning normally now. Thanks for all the help! You guys were awesome! Now I just have to clean up all the other little stuff and fix the electric fans. Thanks again!