Need diagnosis help MAP P0108

[afraptor22]

Lately my truck has been throwing a P0108 code, CEL and going into a limp mode. It only happens on the highway usually above 65mph...which is awesome when the motor goes to idle and makes no power. Turning it off and back on doesn't help, only pulling the power for 10 seconds will reset it and it will run fine until the next random occurrence. Today I was logging when the problem happened, you can see it drop like a rock at 11:44. I replaced the MAP sensor, I have 5.0v at the sensor. I'm using a PSI harness and I don't see any breaks in the wiring loom. At this point I'm thinking bad PCM?? Would appreciate any help!!

[5FDP]

What's the part number on the MAP you are running and do the settings in the tune file correctly match that of the MAP that you are using?

Seems a bit odd that at partial throttle the MAP is going way over 95-100kpa.

[afraptor22]

First one was 09359409, replacement was a cheap O'Reilly part. Both had the same symptoms. 1-Bar, no turbo...just a big snorkel. I didn't change any MAP settings, MAP linear 94.43, Offset is 10.34

[5FDP]

Have you tried running your own wires down to the computer to bypass the pre-made harness you bought?

[afraptor22]

Might try that tomorrow. Seems like a programming or PCM issue since pulling the battery lug fixes it instantly. If it were harness it would take some movement or something to fix it. Is it possible that a quick harness ground in the MAP circuit would cause the motor to go into the limp mode and stay there even if the MAP data returns to normal? It looked like on the log the MAP stuck way high when I was idling, but when I pulled the battery it went right back to normal.

[5FDP]

I'm just spit balling an idea seeing how the sensor has already been replaced and the settings should be correct for that sensor.

A computer issue is always a possibility but normally something I'd think about last.

[afraptor22]

This isn't the PCM that came with the motor, I bought it so I could use this motor with a 6L80e. Was told I needed a later model PCM, so I don't have any history on this one. I was thinking about flashing the old PCM and see if it takes the newer software and runs. Can't seem to sell the thing anyway.

[Lakegoat]

I had a similar problem with no DTC, but the car would die at random times. When it died, the MAP reading dropped so I changed the MAP sensor and tried retuning the idle air/spark and everything else. Finally, I untaped the harness from the map sensor back to the main harness and there was a splice with crimp connectors. I cut them out, soldered the wires and no more problems. I don't know if PSI uses crimp connectors, but might want to check. This drove me crazy for two years. The crimps looked good, but I guess not. I previously thought it was some crimp connectors from the throttle body and soldered them. This was a used harness that I bought when I went from 6 speed manual to 4l80. Good luck.
I passed an 18 wheeler once and pulled back in front of him and the car went dead---bad problem.

[afraptor22]

I had a similar problem with no DTC, but the car would die at random times. When it died, the MAP reading dropped so I changed the MAP sensor and tried retuning the idle air/spark and everything else. Finally, I untaped the harness from the map sensor back to the main harness and there was a splice with crimp connectors. I cut them out, soldered the wires and no more problems. I don't know if PSI uses crimp connectors, but might want to check. This drove me crazy for two years. The crimps looked good, but I guess not. I previously thought it was some crimp connectors from the throttle body and soldered them. This was a used harness that I bought when I went from 6 speed manual to 4l80. Good luck.
I passed an 18 wheeler once and pulled back in front of him and the car went dead---bad problem.

Thanks, was hoping not to have to pull apart the whole harness, but I need to try something else. I can relate, the dead motor at 65mph is no fun.

[afraptor22]

Been playing with this stupid thing all day and getting no where. I ohm'd out all three circuits for the MAP and they are fine. I played with sensor offset and range, no P0108 change. I see that the PCM is setting the code before the motor starts. I also tried a different 2009 PCM and there was no change.

[afraptor22]

Here's the log from driving around today. Cruise kpa still seems high?17-11-16 15-06-30.hpl

[GHuggins]

Resistance doesn't mean anything - what are actual voltages?

[afraptor22]

Key On, Engine Off
5.008
4.774 @ 103kpa

Idling
5.072
1.443 @ 36 kpa

[cjsgarage]

We've seen tons of issues with ordered harnesses. It's one of the main reasons we started making our own, with zero crimps from terminal on sensor to terminal at ecm. Run new wires, or pull apart that crappy corrugated plastic, and look. It goes back on easily enough.

[afraptor22]

We've seen tons of issues with ordered harnesses. It's one of the main reasons we started making our own, with zero crimps from terminal on sensor to terminal at ecm. Run new wires, or pull apart that crappy corrugated plastic, and look. It goes back on easily enough.

It's not the harness. I replaced the wiring from the connector to the PCM and the connector at the MAP. There is now no PSI wiring in the MAP circuit. It still has the same problems.

[Dubersauto]

it's not the harness. I replaced the wiring from the connector to the pcm and the connector at the map. There is now no psi wiring in the map circuit. It still has the same problems.

you ever get this figurted out i have a ls3 in a caprice doing the same thing and did all the same test.

[afraptor22]

you ever get this figurted out i have a ls3 in a caprice doing the same thing and did all the same test.

I don't remember how I got it fixed. I want to say I ended up replacing the computer and making sure the MAF and MAP matched the vehicle the computer came out of. I would get another LS3 computer and unlock it and see what it does.