DevX83z

Have a 1983 z28 HO. Think my ECM might be bad/going bad. Car starts and runs, but not well. Check Engine is always lit. Found the other diagnostic threads and tried to pull codes. Won't even blink a 12. Tried the power off/on to check for blink on startup, and nothing, full solid always. Pulled ECM the other day and found it's a 1226025. Found the replacement(s) at a few reputable sites, which I'll probably trust over the $9.99 ebay special. My question is that the service code (1226025) matches the replacement parts but mine says CCA on it, others I've seen say SA, BKD, etc.

Looking at the PROM inside, it looks like that CCA might be more related to it? I see the info on it that says 3281 CCA. So am I correct in assuming that I can ignore the other numbers on the ECM as long as the service number (above) matches, since I'll be ideally swapping my chip into it? Also, should that not resolve the issue and replacing the chip be my next step, does anyone have any info on where to find one? I turned up some hypertech and jet chips, but even those didn't seem to be the exact match (5.0 HO/MT/1983). Junkyard isn't going to work as I can't find many 3rd gen's let alone this model in my area. I'm not against a hypertech if it's the most cost effective step, but I'm also not after complicating things.. More interested to get this back to running as close to stock and in best possible tune before starting to add/modify anything.

Lastly, this ECM only seems to have ONE swappable chip? It does not appear to be the compound package, just the PROM. I can post pics if it's helpful!

Tuned Performance

iTrader: (92)

As long as the service number is the same disregard the broadcast code and swap in your cca.

DevX83z

Just wanted to jump back in to say thanks for the info/confirmation. I decided to go over everything one last time before throwing money at it. Found a blown fuse, replaced it, and no codes, no light (light works and I pull a code 12 when I go to diagnostic mode), but no light while vehicle is operational. So issue resolved by checking what I should have checked first.

Tuned Performance

iTrader: (92)

Glad you solved it on the cheap too

kurtis72

What fuse was blown?

DevX83z

I forget the exact labeling, but it was the one that would make sense for the ECM. It was marked ECM I believe, or some that would indicate computer/engine management. 10A, I just moved the radio fuse and it worked. However now I'm back to a 'it sometimes works and sometimes does not', so I'm going to replace the ECM unit, as it blowing a fuse, and being intermittent in it's operation is giving me more reason to not trust it.

DevX83z

Updating this as I'm still trying to flush out the real issue. Replaced ECM with a new/remanufactured one. (Swapped PROM). Worked for a day, then again stopped. I swapped back my old unit (factory original), and it worked for a bit. Found some 'creative' wiring under the hood and cleaned it up (smog gear is gone and some genius cut the AIR wires (and others maybe) and connected them.. one was just two power feeds to themselves, but the other were two black and one brown), but suspect there might be more. Here is what I have distilled it down to: If the unit is non-functional, but removing ground from battery, waiting 5-10 min and reconnecting makes it run again for some unknown length of time, what might be the possible causes? I was careful to not move or touch ANY other wiring during this reset period. During it's non-functioning time, I get no MC solenoid clicks at key on, and check engine is on solid. Won't pull any codes either. After the reset, clicks away happily, and no check engine light for the few miles that I test drive it. I haven't yet put the new ECM back in, but it gave me the same result after the first test of it. Maybe bad/failing PROM? as rare as that is?

John in RI

iTrader: (167)

Always hard for me to suspect any part is "bad" when I'm not SURE about the wiring. You've already used 2 ECMs, with basically the same results. I'd double back under the hood and spend a fair amount of time re-checking that the wiring isn't FUBAR.

Sure; could be the PROM - but I'd re-check the all the wiring again first.

Tuned Performance

iTrader: (92)

If it was the prom you would get a fast blinking service engine light.

NoEmissions84TA

iTrader: (1)

I agree with messed up wiring. It sounds to me like it runs until it goes into closed loop mode, and with the wiring being messed up, then it stops working.

DevX83z

Any idea why the power reset (10+ min of battery cable disconnected) gets it going again? Does the ECM need a reset like that when it encounters a failure? I'll keep an eye on it today if I do that, as I don't believe it has occurred while driving, just from a starting standpoint. I can tell immediately as I get no MCS clicking at key-on, engine-off, when it's acting up. (and the more obvious SES/SEL). Thanks for the replies btw.

naf

iTrader: (7)

The ECM itself is powered by the line that runs to the battery post. the fused power is for systems that the ECM controls.

I would suspect that you've got a short somewhere that shows up whenever the ECM commands that particular function. Look at your wiring to the EGR, Canister Purge (might be all vacuum in yours), bump solenoid, MCS, AIR, etc. In this case resetting the ECM could remove the command essentially take the short out of the circuit.

A wiring diagram will show all of the engine control fuse items. Remember that the ECM provides the ground to energize.

DevX83z

Just to wrap this up, I extracted the entirety of the ECM harness from under the hood and went through each set of wires/connectors. Found very little amiss, but did clean up a few prior 'modifications' the PO had made. Put on fresh wire loom and tape and plugged it all back in. With no change in the status, I took my multimeter to the MCS. Infinite resistance! Checked the connector going to it from the ECM while the car was running and I was getting voltage pulses/variations. Ordered a new MCS online for just under $30. Arrived Monday, installed Tuesday. Took it for a 30 minute drive today with no issues. Stopped and started a few times and it remained running. Little by little I'm learning to really, REALLY test everything properly and stop making assumptions based on only half the facts. Again, thanks for all the help!

NoEmissions84TA

iTrader: (1)

Glad you found it.
The ECM coolant temp sensor in the water neck (thermostat housing) is also a common problem.
IIRC, there is a hose that runs right over the top of it that bends the wires 90 degrees, and that connection usually goes intermittent.
GM had a fix for that with a new sensor and 90 degree pigtail for it.

John in RI

iTrader: (167)

THIS !!!

It's easy to overlook - more accurately,.... miss - a wiring/electrical problem because the breaks, splices, and burn-outs to wires are often out of sight. Because really screwy things happen due to a "not normal" electrical problem, ( like wiring in fog lights wrong, or splicing the wrong wires together ) the symptoms aren't normally covered in the "troubleshooting" section of any manual cause they are they are not normal/expected failures.

You might have replaced the ECM and the MCS, but I'm thinkin' the time that you spent fixing the wiring / harness -more than once- to correct past wiring mistakes was probably what got you threw this problem. Time well-spent !!!