nix1981

ECM #1 – Currently installed and original to the car.
No CEL when ignition ON.
When checking codes; no flashing of code 12.
Hear M/C clicking.
Engine starts and runs.

What I’ve done so far:

I ran through CHART #5 but I’m not sure I was checking voltages correctly. As I was checking voltage, I only checked on the connector. It was unclear to me when to check the connector or ECM prongs? When checking voltage on the ECM the assumption is that the connector that is not being tested must be plugged back in otherwise there is no power to the ECM to check – correct assumption?

ECM #2 – spare I bought of Ebay (no known history but is off 81 AT)
Solid CEL when ignition ON.
When jumping to check codes; very fast flickering of CEL.
Do NOT hear M/C clicking.
Engine will not start.

What I’ve done so far:

I did not run through any diagnostic testing.

I’m not sure what to do really. Easy thing to do is run the car with ECM#1 but I don’t know if everything is running the way it should be as I cannot check for codes. ECM#2 will not start (which is odd?), and I’m not sure what that is either… I do have a MONITER to plug into the ALDL, but I could not get that to work either – could not get a good connection kept giving me a “+NO DATA”. This has worked before which is how I knew to replace the O2 sensor. Everything seemed to be running fine.

At this point, I’m thinking of buying a new ECM from ZIP and trying it. Also, does anyone have the correct orientation of the PROM chip? I just want to make sure I don’t screw that up. I read on another post that was similar to my ECM#2 scenario that the PROM was not seated correctly – but then again, that motor would start and run.

Any help would be greatly appreciated.

68blvert

this is for an 82 but 81 should be similar if not the same.

nix1981

Thanks! The 81 is a bit different. I have the service manual etc. Just kind of funky...

Tim81

The Prom should have a notch on one end of it, that lines up with the side that the #1 pin is on or I can't remember but I believe the socket for the prom also has a notch on it, the two notches should line up. Hope this helps.

DUB

YES...if the manual tells you to 'back probe' a specific circuit...then that means to do it while the connector is still attached to that specific component.

The logic would be that you would NOT need to back probe a connector if it is not attached....and usually they will tell you to run 'jumper leads' instead.

I do agree...sometimes the manuals seem to allow for different interpretations.

DUB

nix1981

I'm going to regret asking this... How are you supposed to check the voltage when the connectors are still connected? I'm just not an electrical guy. Hate it actually. If anyone has any pics of how I should be doing this, that would be great.

nix1981

So, quick update. I took and swapped prom chips. ECM#2 and original prom (but now I'm beginning to wonder) and CEL cam on. The paper clip just caused a rapid flash. No code. Went to start and it just went dead. Every time I turned ignition to start. Put ECM#1 and original prom back on and it started. Runs pretty rough, I think. The other thing is that the catalytic converter is HOT and smells HOT. I'm really frustrated because everything seemed to be running fine. Ive never had a hot smell like that. Could it be that the everything needs to reset? I've got a new ECM coming tomorrow that I'm going to try. By the way, the two prom chips have different numbers? Any idea of what the part number should be? My monitor code reader wont even work keeps saying no data. I know there's a lot in this post, but I really hope someone has some idea of whats wrong.

DUB

Hopefully this will helps you and I do not mean to be direct...but it is how it has to be.

GOOD POINTS:
You have a manual.
You are asking for help in areas you are not familiar with.
You ahve teh desire to learn this stuff and repair it your self.

BAD POINTS:
If swapping out parts because you are 'hoping' that you will find the correct sequence. And get it running right is NOT fixing it by doing ti this way UNLESS you know what you are doing. Doing this can be extremely dangerous....thus...cost you MONEY!

How you find out if a circuit has power when it is connected is done by back probing it with a tool that will allow you to go in from the back of the connector and make contact with the terminal can check it. IF the connector does not allow you to see the terminal from the backside...then that is when you have to do like I do and spend money on special jumper leads that allow you to connect to each circuit and them will allow you to test them. SO...you can make a jumper wire with an alligator clip on it and clip it to paper clip , sewing needle or even a piece of wire you have stripped and make contact with terminal you want to check. JUST MAKE SURE that IF you do this...and you have your alligator clip exposed and can see the metal clip. You DO NOT want these alligator clips OR any part of your test leads that are exposed wire to touch a power source or a ground. Because that can really screw things up...and that all depends on what you are testing. A simple mistake by ground a wire you should not ground can FRY a delicate electrical part. JUST SAYING....PAY ATTENTION to what you are doing.

Your catalytic convert getting hot can be due to excessive fuel you have not burnt due to many tests being done while cranking it and it not running.

IF your scanner is NOT giving you data....you need to VERIFY the serial data line from your ALDL to the ECM and make sure that that wire is GOOD. If it is...you have a problem in the ECM or PROM or BOTH.

It is CRITICAL that you can read live data...without it....you are literally flying blind.

YES...it is highly likely that the system needs to 're-learn' by you driving it above 45mph so your IAC's can reset. Also...IF you can finally read data...this will allow you to look at your INTEGRATOR value, TPS voltage, MAP voltage and COOLANT TEMP.

Your car may run fine when it is in OPEN LOOP....but I have seen them go crazy when they go into CLOSED LOOP. SO...hopefully when you get this running and can read data...you can see that the computer is going into CLOSED LOOP...which is what you DO WANT. AND..to get the computer to go into CLOSED LOOP...the OXYGEN SENSOR has to get hot enough to do so. This usually occurs when the coolant temp get to about 170 degrees Fahrenheit.

AND...if you notice that you are getting into CLOSED LOOP....but then it goes back into OPEN LOOP. What that is telling me is that the fuel circuit is a bit rich...putting more fuel in the system..and this added fuel is now allowing the OXYGEN SENSOR to cool back down and causing it to switch back and forth. And this is why GM now has HEATED oxygen sensors. And a few things can cause the fuel system to go rich.

DUB

nix1981

Thanks DUB! I managed to take a breath and go back through everything today. Worked through the 'charts' and felt pretty certain that the ECM was the issue. I also spoke with ACDelco about the PROM chips. Both are stamped 6079 FO (one took some UV light to see) and I'm told is 'right' for my car - 81 AT non CA. They have some other numbers, but they said not to be concerned with that? I also received the new ECM, so I gingerly took one of the PROM chips I thought was best and hooked the new ECM up. Turned the key to on... CEL! Checked for code 12...got that too and nothing after that (just kept flashing 12) - why would there be with a new ECM, right? Started the car and I immediately felt and heard a difference. It's raining like a SOB here in VA so I did not take a drive to cycle everything - I'm hoping for a break in the weather this weekend. The Monitor85 is also now reading. I realize I need to run the car a bit, but for now, I think the ECM is working the way it should and I can start watching what the car is doing to see if there are any other issues that may arise - a good drive will tell.

nix1981

@DUB I was able to drive around a bit and wanted to comment, or get your futher comment on the OPEN and CLOSED LOOP. Got the Monitor 85 going and the car indeed would toggle from OPEN to CLOSED. Not in rapid fire, but it would be OPEN for a bit then CLOSED then OPEN...just as you described in you last comment. I'm assuming that this is normal and a flaw in the NON heated O2 sensor...is this a correct assumption or should there be something else to take a look at? DWELL is a 30 degrees, RPM is at about 600 (idle and after a small adjustment). FWIW, the cat seems to not smell so HOT either. It did while starting and restarting a few times but as I drove a bit and let it idle a bit that burning smell was gone.

Thanks in advanced btw! You've left many comments on my post and some others that have been extremely helpful!!!! In fact, probably saved $$$ not having to run to talk to the shop! One day I hope to be able to pay it forward.

Antz81

If it's doing this while at low rpm and idle it's just the o2 sensor as you have suggested.

DUB

Sounds like you got it.

I can not confirm this 100%...but it came from a very reliable source. When I am messing with an ECM that has a chip...I make sure I do not allow light to get to the chip. From what I was told ...light can damage it by 'removing memory' that is in the chip. So..I err on the side of caution and always cover it or put the plate back on the ECM.

DUB