Extreme rich condition

[Hib Halverson]

If the MIL is on but there no fault codes, then something is messed-up with the engine controls installation and, as this is an LT5 into 1G Camaro using an aftermarket harness, it might be difficult to solve this problem.

Is the calibration in the ECM also from a '91?

[Perry Mitchell]

Yes, the ECM and the recalibrated prom are from the wrecked 91 Z

[-=Jeff=-]

Yep Hib posted before me.. if no codes but an SES. You need to confirm ECM and PROM on someone?s 91z. Then if those work fine, look to the harness..

[Marc Haibeck]

It looks like everybody's ideas are heading in the same general direction. If the ECM blinks a code 12 it means that the ECM has passed the power up self test. That suggests a good ECM.

Is the chip adapter module plugged in 100% into the socket?

However like Dominic pointed out, if the engine is running and the SES is on with no error code set, the ECM may be running in limp home mode. In limp home mode the engine will run like you are describing, rough due to low spark advance and very very rich with fuel.

Like Jeff said, test the ECM in a ZR-1. You can install it in any model year ZR-1. You will get a SES and different error codes depending on the differences from '90 to '95. However, if the ECM is good the ZR-1 will idle smoothly and without excessive fumes.

[XfireZ51]

So just to summarize,

1. You have a 91 ZR aftermarket harness, no CCM
2. A stock C4 ZR ECM that flashes a code 12
3. A re-calibrated stock prom using a 91 Mask ID, or is it a recalibrated prom on a daughter board?
4. You have verified pinouts for ECM to aftermarket harness
5. An SES light that comes on immediately upon startup.

Am I missing anything?

[Perry Mitchell]

Originally Posted by XfireZ51

So just to summarize,

1. You have a 91 ZR aftermarket harness, no CCM
2. A stock C4 ZR ECM that flashes a code 12
3. A re-calibrated stock prom using a 91 Mask ID, or is it a recalibrated prom on a daughter board?
4. You have verified pinouts for ECM to aftermarket harness
5. An SES light that comes on immediately upon startup.

Am I missing anything?

That about sums it up. It has a stock re-calibrated prom, no daughter board.

[Perry Mitchell]

Originally Posted by XfireZ51

If the SES light is on steady, then its in Limp Home mode which would dictate it to run rich. And you say you have no codes altho the SES would indicate there is(are). How are you reading for codes?
I would follow Jeff s advice on getting a scan tool like ALDLdroid.

First off, I would like to express my appreciation for all the help you guys are giving me. I
have ordered an ALDL to USB cable as Jeff suggested. I plan to use it with my laptop. Hope I can figure out how to use it. I also have another ECM that I bought years ago. It is a re-man from Delco without a prom. I will swap them out which should eliminate the need of finding another ZR1 owner in my area.

[XfireZ51]

The ECM isn?t reading the prom and so its in Limp Home Mode which uses a static fueling and spark map just to do what it says. If somebody nearby has a 91 prom, u could throw that in first and see what happens. It?ll probably start the motor, just not very drivable. If that happens then prom may be corrupted. My guess is that or wiring is suspect in that order.

[Perry Mitchell]

I just swapped out the ECM with the re-man unit that I have and found no difference. I am sure Marc checks out the prom during the re-calibration process. I will recheck my wiring AGAIN. I rechecked my SES again. With the ignition on the light is on steady. Turn ignition on, jump the A and B pins in the ALDL and the SES light blinks a 12 code. Start the motor with the ALDL pins jumped and the SES light blinks rapidly. Then I pulled the jumper off while engine is running and the light goes off. I hope that makes sense and that I'm not bothering you guys too much.

[-=Jeff=-]

I don?t feel you are bothering us. The symptoms are just odd.. that is all. Do you have wrong schematics with details you can share? It is hard to diagnose some things without info like that. How is the SES wired in the harness??

Calibration. Is probably fine. What are the numbers on the ECM, you say you have a remanufactured one.. from where? When did you get it? Let?s confirm the ECMs are correct