1993 LT1 Automatic

I have been having performance issues that I narrowed down to an issue with my ECM (crank no start when hot, put ice pack on ECM starts up fine, Also startup fine when cold. runs bad when warmed up). I sent the ECM to SIA and they reflowed it and said it was testing good. When I received it I plugged it in and no start. Jumped ALDL pins A and G had Module 1 C41, Module 4 "Err" and no codes on module 9. Made sure prom was properly seated and tried again with same result. Jumped ALDL pins A and B ECM flashed code 12. Sent ECM back to SIA, they reflowed again and said they had serial data. While they had it I pulled the CCM to follow flow chart in FSM.

E13 - D4 = Continuity - good
F12 - D4 = Continuity - good
E13 - D15 = Continuity - good
F12 - D15 = Continuity - good
E13 - GND = No Continuity - good
I/P to Derm harness fully seated
ECM and Airbag fuses good

Got ECM back from SIA, plugged in and still Module 1 C41, Module 4 "Err", Module 9 no codes
ECM will flash codes with SES light, only code 12 flashed

Check continuity for ECM power feeds and grounds,

Power feeds:
C6 - Battery Positive Cable - continuity good
C17 - B+ - continuity good

Grounds:
B6 - Battery Negative Cable - continuity good
B17 - B- - continuity good
B22 - B- - continuity good
C12 - B- - continuity good
D17 - B- - continuity good

I have read that the ICM can cause this issue but in the FSM the ICM would throw a Module 4 C41 code, or flash 41

I am lost and unsure where to go next. Any help would be greatly appreciated.

 

That sucks you are having all of this trouble. When I had ECM issues in my 93 SIA reflowed it and it has been perfect since…

have you double checked your memcal is seated properly/tried to reseat it?

You need to make sure your serial comm line is not shorted or broken. I know you said you did some tests but you need to check the tan comm line.

C41 means the CCM cannot talk to the ECM. Same reason for “Err” on module 4. It also won’t start because the CCM after VATS check sends a fuel enable command to the ECM via that same comm line. If that doesn’t happen the ECM will not fire the injectors.

extra troubleshooting and talks about the wires to check:
https://www.corvetteforum.com/forums...ol-module.html

 

Thanks for the reply.

The test for continuity between the following pins are the serial data lines between the ECM and CCM

E13 - D4 = Continuity - good
F12 - D4 = Continuity - good
E13 - D15 = Continuity - good
F12 - D15 = Continuity - good
E13 - GND = No Continuity - good

As far as physical inspection I haven't done a full visual yet but the portions that are visible appear fine. The reason for not physically inspecting the lines yet is that continuity shows good. I haven't checked for shorts because the manual states that a short will take down the entire serial data line including the Electronic Brake Control Module (Module 9) and I still have communication to that. An open will take down only the affected module and since I have continuity where I am supposed to the likelihood of an open/broken line is low (but not impossible).

The odd thing to me is that the problem was intermittent until I had the ECM reflowed and now there is no communication at all. My next move is to get a pin extractor tool and start investigating the ECM connector D where the serial data lines pass through. Its possible that the serial data line pins are not fully engaging the pins on the ECM even though the connector is completely seated.

Also yes I have ensured the Prom is seated correctly. And thank you for the link to that thread. Interestingly SIA actually sent me a print out of the steps in that same thread when they sent the ECM back to me the second time.