Rbuet

Car is a 1995 LT1 6-speed.

My car has been out of service now for 3 months and I need help getting it fixed. I have spent an uncountable number of hours following the FMS and searching archives with no luck.

Here is my problem:
- DTC 41 from CCM - Serial data link
- DTC 54 from CCM - FEDS failure
- DTC 72 from Mod 9 - Serial Data line malfunction.
- DataMaster can not read PCM.
- C68 head flashes green light on/off.
- Car will start great, but only run 2 seconds before it shuts down.

I removed all modules from the Serial Data Link. (DERM, C68, PCM, CCM and EBTCM) Continuity is good on all parts of crt #800 (Serial data line). Continuity to ground is good. No voltage on Serial Data Link with no modules connected.

When I put the CCM back on the Serial Data Link by connecting the green connector to the CCM, I suddenly measure 4.8 volts consistently on the Serial Data Link. Should this type of voltage be on this line, or is this possibly what is bringing the Data Link down?

I have replaced the PCM twice with AcDelco remanufacturer units with no change. However, I have not been able to reprogram the PCM with the tune I got from PcmForLess becuase the Serial Data Link is down.

I did post about this problem two weeks ago - See "DTC 41 - I need help", but after trying two different remanufactured PCMs with no change, I am not sure what to try next.

Can anyone help???

Randy93

Did you check the wiring?

TPIGUY

Try this, I've seen this same porblem. When you turn the key on, the fuel pump runs for a couple of seconds, then shuts off until the oil pressure switch at the rear of the engine senses oil pressure and turns on the pump again. If your car starts and runs then shuts off, it could very well be the oil pressure switch. An easy way to tell is by attaching a fuel pressure guage to the pressure port on the fuel rail. When you turn on the iginition youll see a pressure of 30 to 45 lbs. When your engine stops after a few seconds check to see if your maintaining fuel pressure. No pressure, no run. Hopefully it's something this simple. Don't give up. You can do it!

Rbuet

From the OP: Thanks TPIGUY. I just tested the fuel presssure and found:

1. Key on - 45lbs pressure while pump runs.
2. Pump turns off - Pressure drops to 5 lbs in 15 seconds.

This does not seem right! But how does that relate to CCM DTC 41?

I recently installed a new Areomotive (sp?) AFPR. Could that be a problem? I need to look at my FSM!

I'm back off to the garage. All suggestons welcomed.

TPIGUY

Yes, but does the fuel pressure stay up after you start the car? You sai the car runs for a couple of seconds and dies. Whats the fuel pressue doing as you start and run the engine?

Rbuet

Ok, I'm back from the garage. Turned key, 45 lbs fuel prerssure. Car started immediately, 45 lbs while running. 45lbs when car dies two seconds later (fuel pump still running). After pump turns off, pressure drops to 5 lbs quickly.

Ron

TPIGUY

Well, that seems to be working as it should. Except you should be able to hold pressure longer after shut down. But lets not worry about that now. Let me do some checking.....

Rbuet

Any more ideas, anyone?