ECM questions

[tomtom72]

Hi guys, Please forgive the elementary Q's but I truly have no experience to draw on.
I have a 90 ZR-1 & I think there is a possibility the ECM may need to be replaced.
Is the "chip" called a PROM, that thing on the underside of the ECM?
Dose that come with a new ECM or is it bought separetly?

I tried "drilling" down at some GM parts sites & tried to find a part listing for a PROM but I couldn't.

Thanks for any help,
Tom

[Kevin]

The "chip" is the prom and is accessed by turning the ECM over and undoing the bolts and pulling the cover off. The Prom is not part of the Ecm package when you buy it from gm. My advice is to go after marker with the prom and go with mark haibeck or someone like that.

[tomtom72]

Thank you Kevin. I didn't want to be totally ignorant when I have my car scanned by a diagnostic machine & not know the correct terms.

Is it possible to tell by using a scan tool if the ECM &/or the PROM are faulty?
I don't know if that is a valid question? I wish I could find some reading material that explains electronic engine controls to non-tech persons like me.

Thanks for your time!
Tom

[Kevin]

Tom,
What is the car doing that you need to have it looked at

[Nick]

Do you have the service manuals?

[tomtom72]

Hi Kevin, Hi Nick,
Yes I do have the helm manuals for the car. I have little to no experience with electronic engine controls & fuel injected cars from a "hands on" aspect.

The car is sputtering and it seems to have a miss. I thought water in gas, so I added techron(big bottle) & replaced the fuel filter. No joy. I next pulled all plugs; even # plugs had clean, white center porcelians, which seemed odd as the electrodes were charcoal; odd # plugs electrodes & center porcelian were charcoal. No visable damage, no fouling, broken parts. I had my FR2LS plugs saved so I put them in & no change. Resting state battery voltage is 12.5, I knew I wasn't gett'in lucky!

I had no SES light but I used Gordon's jumper kit to look for codes in the ECM and the CCM. 12 in ECM and --- in CCM so I went to 6E section, and checked fuel pressure, 50psi on KOEO tests, engine cold & 48psi with engine running @ hot idle. I used my inductive timming light to check the wires & get a feel if there was energy in all wires, and I had good light pluses on all wires. I put a Vacuum gauge on it also & 15"hg @ idle speed, hot motor. I did all those checks while I was warming up the motor to get fuel psi w/ motor running. Book said KOEO PSI tests w/cold motor & hot motor for running PSI test. I found no fuel in pressure regulator hose & since the PSI w/ motor running was good I figured the regulator was good. I put 12" hg on it w/ motor off and it held vacuum. The MAP hose was on & since it was only $30 I swapped it, no change. I smells lean to me so I figured no vacuum signal to ECM for A/F adjustment. Just a guess. I should know better.

The rest of the stuff in book talks about a Tech1A so I figured I need to have it scanned. I was afraid of what chart A-7 said about looking for spark & the cats so that is why I used my inductive light. It always worked on my 72 LT-1 & it had GM C/D ignition and I also checked the FR2LS plugs for wetness after swapping them & the fuel filter because I could tell right away the "miss" or "sputter" was still there. Also the exhaust smells lean. I figure big vacuum leak or all the injectors quit at once? I hate to say this but I feel like blocking the T/B extension but usually a vacuum leak leads to high idle & mine is normal, 600 or there abouts. Oh and this throws me, it started to sputter or miss very subtly and by the time I went about 5 miles it was a full miss. I also turned on the power key and it was the same miss. That's why I thought bad gas because I just tanked it. I siphoned out about 5 gals worth & let it sit to check for water, no soap. With no codes I'm quite lost as I can't take the odds of all 16 injectors going at the same time, and I figure if the O2 sensors were N/G it would be in "closed loop" only? I guess if no sensors actually break I wouldn't see a SES light & codes. I just don't understand enough to be very effective at trouble shooting, guess I should have went to Gordon's school before buying a Z.

Thanks for the sincere inquires & the knowledge you all share with us rookie Z drivers.
Tom

[Kevin]

code 12 is a check code. to check the injectors get the car hot, pull the plenum and use an ohm meeter on the injectors. 12.5-13 is what they should be at..

[Aurora40]

Short answer from someone only mildly informed. The ECM can detect errors with itself to a degree. Obviously depending on how it is flawed, it might not do that. I suppose diagnostics could help narrow this down. Another way would be to just swap the chip. If your car had the recall done, do you have the original PROM? Would be a quick way to rule it out.

Also, just to clarify, by "check code", that means that code 12 is always there. It means nothing except that the code checking procedure is working. You will always get 12, next code, next code, etc. So if there are no codes, you'll just get code 12.

Edit: just a quick also, each code will flash 3 times. So make sure you are waiting through 3 instances of "12" to see if there is a next code.

[tomtom72]

Thank you Kevin for the ohms readings. I must have missed that in Sec. 6.
I read on CF that there is a way to check the ohms thru the ECM connector, but the post was a bit over my head. Anyone ever do it that way? How is that done? I'm not garaged so I want avoid the plenum for now as I'm in the process of securing a rented space to do that work over the winter. Thanks for your help!

Hi A40, Yea I have Gordon's book & jumper modules & he explains the drill so even the non-EEC people can read codes. I waited, in fact I did the ECM & CCM. The local independent tech I spoke with laughed when I told him about my troubles. He said..."Those EEC systems from back then are retarded. The ECM might have lost a ground or it could have quit on you, outside it might be the MAP, but I doubt it. Did you check the grounds?" I couldn't say much because I don't know much. I have all the paper from the orig. owner & it seems not. I don't have a dealership receipt for that. I can say my guess would be no it wasn't done because it has the symptoms. Thanks for your time!
Tom, I should have done GK's school.

[Kevin]

I'm not sure how to do the ecm test on the injectors but pulling the plenum is quite easy.