LMM: Max rail pressure issue after headgaskets.

motoking_1990

motoking_1990

Active member
May 9, 2011
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Terre Haute, IN
Did headgaskets on a 2008 lmm. Have done a lly once before. Well everything went fine until i started it. I knew instantly something was wrong. It was louder than usual which instantly made me think rail pressure. Sure enough has max rail pressure at idle. It was throwing a bunch of other random codes at first egr, intake air flow valve circuit, p0090 fuel rail pressure circuit 1, reduced power. I had Mark at danville make him some tunes since it was deleted and everything. Loaded the tunes all the codes went away except the rail pressure. So far i have done the following, pulled pigtail test resistance making sure the wires were good internally. Made sure the return line going back to the tank wasnt kinked which at one point it was in a bit of a bind. It was good. Pulled bale connectors apart tightened the connectors on it. Took two grounds off during head job. Both of them are hooked up. I tested the voltage going into the regulator at idle it was 10.4 volts which from what i read is wrong but nothing on what would cause it. Is it possible the regulator just randomly took a dump?? Could a tiny piece of debris gotten into it somehow and is messing with it? He ordered a new fpr from merchant dont know when it will be here yet.

Any opinions or ideas would be greatly appreciated.


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coker6365

coker6365

Coker6303's ***** Daddy
Dec 4, 2011
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The cam and crank position connectors only lay relaxed 1 way. Longer wire should be the crank position. However, if you have then swaped it can for some reason simulate what you are seeing. My brother did this when he swapped an engine in his 2015, he chased a weird rail pressure issue and after a week of us giving him a hard time, he finally realized he had the cam and crank connectors swapped.

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motoking_1990

motoking_1990

Active member
May 9, 2011
1,957
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38
Terre Haute, IN
Well the wiring seemed to only go one way to keep it away from the belt drive. And there is a ground on the same end of the harness. I tried it both ways originally but the ground wouldnt reach unless it is rhe way it is now. But i will try and swap them and see if that solves it.


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ironmax

ironmax

chock full of goodies
Jul 7, 2010
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Col. Ohio
I had a similar issue with rail pressure on an 08 lmm after I swapped a turbo. The cp3 reference wires tested fine unplugged, but once it was plugged in to the cp3 it lost the connection.had a break in the wire inside the insulation. Did you try fiddling with the wires when they were plugged in to see if she quiets down?
 
ironmax

ironmax

chock full of goodies
Jul 7, 2010
502
27
28
Col. Ohio
www.duramaxdiesels.com

P0090 issues

I have been chasing a issue with an 08 that I deleted. while I had it apart I cleaned up all the soot buildup changed the t-stats and flashed in the new programming. When I started it up I got the P0090, from there I started to check my wiring harnesses. Can anyone tell me which wires in the frp...
www.duramaxdiesels.com www.duramaxdiesels.com
Found my old thread. The wire was broken inside the connector.
 
motoking_1990

motoking_1990

Active member
May 9, 2011
1,957
5
38
Terre Haute, IN
TheBac said:
How the heck do you do that?!? :LOL:
Click to expand...

To be honest i have no idea. I was 99% sure i left the alternator plug into the alternator and pulled them both together and left the cp3 pigtail plugged into the harness. Dont know what happened exactly but we swapped them two and it runs like a dream.


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