JimLentz

I recently purchased a 1992 LT1 coupe with 41,000 miles and drove it home from Michigan, about 240 miles. The drive was uneventful and the car ran well. I have had the car for 3 weeks. Late last week I was driving it home from work and the Check Engine Soon, Check ASR and Security lights all came on and the A/C stopped blowing cold. I just checked for trouble codes and got the following:

27, 28 and 69

1. CCM
H41 - Loss of ECM serial data communications
H74 - LED display dimming output circuit open or shorted to ground

4. ECM
H27 - Exhaust gas recirculation (EGR) vacuum control signal solenoid valve circuit
H28 - Transmission range (TA) pressure switch assembly fault
H69 - A/C clutch circuit

9. ? for 1992
H72

Are the symptoms I experienced due to temporary loss of serial communication between the ECM and CCM? After I got home I turned the car off and everything was then fine.

WVZR-1

I believe that you clear all and then drive again until you get a similar failure maybe recording time/mileage "today" and the next "failure date".

When you post back maybe mention the code error vs. module and number. Someone has to do nearly as much of a read to answer the post as you might have had to do for diagnostics.

You might maybe consider cleaning/confirming G201 and G106 (Cluster/CCM respective grounds).

Do you have the FSM?

JimLentz

Thanks, I added the codes descriptions I could find. I do have the FSM that came with the car. When it cools off a bit I will check the grounds. Thanks!

9T3VETTE

Mine had the same module 1 & 9 dtc's when I diagnosed the ecu to be bad. The car also bogged on acceleration and smelled very rich. Try tapping the ecu when it's acting up to see if the condition changes.

JimLentz

What is the best place to get a decent ECM?

9T3VETTE

Unfortunately they are quite rare and expensive if you find one. I sent mine to SIA electronics for diagnosis and repair. They found a small solder joint that had failed. It has been fine ever since

JimLentz

Hopefully tonight I can check the ground connections and connectors on the ECM. I drove the car to work today and 3 times the problem happened intermittently. The lights would light up and the A/C go from cold to warm, but in a few seconds recovered (last time only shutting down and starting the car cleared everything up). The ASR Service light went on and stayed on the first time it happened this morning. I am looking around regarding ECM repair or purchase. They aren't easy to find.

JimLentz

I got ready to leave work and the car died almost immediately with the Check engine soon and ASR lights on. It started right back up with no codes. I stopped at a grocery store and on the way to visit my Mom the lights came on for a bit with the ASR light staying on and the A/C was blowing warm air. The ride home was uneventful and I decided to leave it run in the driveway with the A/C and wiggling the ECM wires and tapping it had no effect, but I noticed the coolant temperature kept going up and got to 220 before I decided to turn on the A/C which forced the fans on and cooled the coolant down. Then I remembered when I first jumpered the A and B terminals to get the ECM codes it also caused he cooling fan to run. Something very odd going on there. I am going to look at the FSM, but the ECM sure seems to be getting worse.

9T3VETTE

Send it out and be done with it

JimLentz

I am going to check with SIA electronics.

JimLentz

I am sending the ECM to SIA Electronics today and while looking for their eBay ad so I could pay them through eBay I stumbled across a working ECU from a 1992 Corvette for $180 and purchased it. If it really is working that seems like a deal and might need a MEMCAL if it is from one with an AT. I usually am not the kind of person that likes keeping spare parts, but the ECM is hard to find at a reasonable price.

JimLentz

I received the ECM back from SIA and they re-flowed the whole board. I installed it and will drive it around and see how it goes. I went for a 2-3 mile drive and at least so far it is fine. I also purchased an ECM with the wrong MEMCAL and ordered a BAFL MEMCAL for my car/ECM as a spare. All this stuff is getting hard to find.

JimLentz

What is this hose and why does it seem to be too long and have to bend at 90 degrees or so?



Very bad hose

SELLC

It appears to be your distributor vent hose, but I cant tell where it's going so don't quote me on that.

It also appears to be very close to your throttle, might want to do something about that when you fix the hose.

JimLentz

That could be as the PO said he added an MSD vented Opti.

JimLentz

So far the repaired ECM has been functioning perfectly. I did some short drives this past weekend and drove it 20 miles to work this morning.

9T3VETTE

Good to hear

JimLentz

You made the right call.