PCM bricked while

[Chuck L.]

driving???
Was doing some logging for initial tuning on the 05 Hummer engine in my 55 Chevy.[Stock PCM]
Got the cold start done, NP.
Started the drive logging. Went WOT for a short distance, [<mi]. Got a very loud backfire and engine quit. I saved the log.
Was fun while it lasted!!:hihi:
Will not restart, nor turn over w/ the starter. No FP prime, no ALDL connection. [Reports no vehicle found] $0280?? Tried the bench harness>> Got the same code.
Checked all fuses. OK
Checked for 12v to pins 20 and 57 on blu connector/good. Power is OK to the ALDL.
I thot maybe the engine scrammed.. Appears to be OK. Plugs good, turns w/ wrench on balancer bolt, no H2O in the oil pan, etc.

Is it usual that the PCM would just die like that?? [Only has 15K on it]:confused:

Found some posts by TAQ back in 07.. Read and failed to "comprehend" them.
Did a "jump" on the neutral start and FP relays. Those systems are working.

Update:
DFE1 and I tested the pcm w/ his bench harness. Worked fine. Found my harness was missing a ground wire connection. Corrected that. PCM worked fine.
Tested all 12v wires to the blu connector, from Howell fuse panel. OK.
Tested the plug in the start/run power feed. OK [Could have been flaky??] Don't know.
Reinstalled the pcm. Previously failed systems, [neutral start & fuel pump] work.
I have yet to start it. Am going over ALL the elec connections in the entire car....

Thanks for listening.....

[Blacky]

Interesting, keep us posted on what you find...
Regards
Paul

[Chuck L.]

Interesting, keep us posted on what you find...
Regards
Paul

Just completed a check of all elec devices and connections.. Found no issues.
Rechecked the operation of the fuel and start relays, checked for fault codes,[none found], and turned the key. Engine started immediately, and began the warm up routine.
Tomorrow, it's some drive time logging.
A review of the run log when the backfire occurred, show the tps at 99.6% for a considerable number of frames, even tho I IMMEDIATELY got off the pedal. Tach signal did not cease immediately, either.:confused:
I do not have fuel psi logging capability, but am planning on adding it.

I can post the log if anyone is interested in seeing it....

[Blacky]

Just a stab in the dark... is it possible the backfire went back out through the intake manifold and impacted the throttle? Maybe its sticking a but now? Can you check with the scanner - see if it hangs for a while after you let your foot off the pedal.
You didn't happen to have the pedal position PID logged in that log file as well - that would tell an interesting story?

Or can you get the freeze frame DTC data - maybe the controller saved some history data when the engine cut out.

Regards
Paul

[Chuck L.]

Just a stab in the dark... is it possible the backfire went back out through the intake manifold and impacted the throttle? Maybe its sticking a but now? Can you check with the scanner - see if it hangs for a while after you let your foot off the pedal.
You didn't happen to have the pedal position PID logged in that log file as well - that would tell an interesting story?

Or can you get the freeze frame DTC data - maybe the controller saved some history data when the engine cut out.

Regards
Paul

I haven't pulled the CAI off, but have looked at the log... Appears that the throttle was stuck @ WOT, clear up until I saved the file, and turned the key off.
Also, the VSS never dropped, even tho the car was parked...

Here's the log I made when the problem occurred.
It appears you are right. The throttle never left WOT position. Time to pull the t/b off, even tho it starts and idles OK...
NE 1 have comments?
Thanks!

[Blacky]

I can't explain the TP and VSS signals being pegged at those values. That is strange. One possible explanation is the PCM may have had a problem that caused it to stop transmitting the TP and VSS PID values. If the EFILive software does not get updated values for any PID(s) from the PCM it will continue to log those PIDs' current values. Some of the other PIDs' values (O2 sensors and IAT and ETC) were still updating after the RPM went to zero, so the PCM was still transmitting some rational data.

With the engine off, and logging the throttle position, does the throttle still stick after hitting wide open throttle? Or is it behaving correctly?
Also, does the VSS read correctly now?

Regards
Paul

[joecar]

Hi Chuck,

So you think it was that missing ground wire...?

Log looks like PCM just hung up... SPARKADV goes to 55 (PCM reports this to V2) and shortly after WO2AFR (LC-1 reports this to V2) goes to 120... this tells me there might be a ground/power connection problem in harness and/or battery/charging system.

TAQ had found his battery was moving under hard acceleration and shorting the terminals on the fender sheetmetal.

Does it work right now...?

[Chuck L.]

Hi Chuck,

So you think it was that missing ground wire...?

Log looks like PCM just hung up... SPARKADV goes to 55 (PCM reports this to V2) and shortly after WO2AFR (LC-1 reports this to V2) goes to 120... this tells me there might be a ground/power connection problem in harness and/or battery/charging system.

TAQ had found his battery was moving under hard acceleration and shorting the terminals on the fender sheetmetal.

Does it work right now...?

Joe/Paul...
Thanks for the responses.
I've checked the t/b for damage, and cycled the throttle w/ the scanner hooked up.. found no issues.
I started it.. It lit right up, and idles fine. Am driving it today, and will log it. [This time I head TOWARD the house when I hammer it. Maybe I can coast home!]

Joe, the grnd wire issue was on my bench harness, not on the car.
Here's a link to LS1tech.. Someone else has reported a fp relay drop out.
http://www.ls1tech.com/forums/pcm-diagnostics-tuning/1428340-losing-fuel-pump-realay-signal.html#post14980496
I'm wondering if I had a fuel issue, it went lean, thus the backfire?? [FP logging is next!]
We have added batt volts to the pid list. My batt is fresh new, had 12.6 in it when I put it in, an hr B4 the incident. It's in a plastic batt box and has no way to wiggle or short to the body.
Only other source I may revisit, is the key switch. It's new, but?? A drop out on the on/run wire[s] could explain what happened, and why I had a "no start" after the incident..

Again, Thanks for the help!

http://www.ls1tech.com/forums/pcm-diagnostics-tuning/1428340-losing-fuel-pump-realay-signal.html#post14980496

[Chuck L.]

Was driving to the ft end alignment shop. Drive time was about the same as when the first failure occurred.
At 35mph,,, WHAMO a dead player!:doh2:
Got off the street, and began a search for the cause.
Luckily, I had left the test lite and the jumper for the start relay, in the floorboard.:hihi:
Instead of looking to the PCM, I disconnected the key sw power to the 4 fuse panel. No power, either w/ key in start or run.
Used the jumper to get going. After the alignment, I drove back to the shop, parked the car, and went to lunch...About 1 hr, maybe 1 1/2.
Tested for power from key sw...GOOD TO GO!
Checked every plug, again...no problems found.
If it was a PCM heat/failure, the power would still be there, but the PCM would have scrammed...
My conclusion: The key switch has a heat related, intermittent failure, or???

New sw on the way.. More later..

[joecar]

Did the switch get hot...?

[Chuck L.]

Did the switch get hot...?

Joe, the ft face didn't appear hot. Due to it's location and surrounding "junk", I couldn't get to the rear section and wire plug[s].

[Chuck L.]

Received the replacement sw and key set. It's in and running.
Drove it for about 20 miles....So far running fine.
Original switch and key set have been returned to AAW for testing. More when I get the results...

[Chuck L.]

AAW tech reports nothing wrong w/ the switch I sent back.:doh2:

Drove the car another 50 miles....So far, so good. while installing the new switch, I
did find a suspect plug on the main harness from the AAW panel. I tweaked the pins, and added a ty wrap as the lock on the connector body didn't "clik" when pushed together...Hopefully, this is the end of the problem.

Murphy and I are going to take a trip next month.. I'm sure w/ he being along, I'll find out if the problem is really solved!!:hihi: