I'm out of ideas

95-12valve

95-12valve

What's a CP3?
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Jan 3, 2009
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04 LB7, replaced head gaskets, developed wiring issue after head gaskets.
Wiring issue solved.

LBZ regulator, DSP-5 tuned for regulator. Went to test drive the truck on Tuesday, got to the end of the drive way and this is what it started doing.

Desired rail pressure fluctuated, actual flucuates(obviously) and it does this. Will idle perfect and all of a sudden go to doing this. I'm out of theories. I've had 2 different, known to be good regulators in the pump. If anyone has any more ideas please feel free to chime in as I'm about to lose my mind... Thanks
 
Truck is a clean emission fleet truck BTW, like a California truck but not completely, it is it's own animal. Injectors are relatively knew(I replaced them) All filters are new.
 
After researching more and diagnosing with a GM tech friend we think it's a CP3 issue
 
Is it a locked tune? Do you have a V2 to log it? I would log desired VS actual rail valve current and see if they are matching. Some LB7's require quite a bit of tweaking to get them to idle with an LBZ regulator.
 
I've tweaked it already and it idles perfect at first then once it warms up a little it'll all of a sudden go chitty and act stupid
 
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I'll log that PID tomorrow and see, I've had an LBZ and an LB7 regulator in it, and today I put an LBZ regulator I know is good in.
 
I think you need to spend some time tuning, if you have had good regulators on it.
 
I don't think the tuning is the issue, this same tune is in many other trucks I've done with zero issues. It Did the same thing with an LB7 regulator.
 
It has also developed a fuel leak, which appears to be coming from the valley, which I'm going to investigate tomorrow. Everything so far is pointing me to the CP3.
 
Had a truck do this once turned out to b going in and out of high idle. So i traced the wires from the coolant temp sensor and found one at the main engine harness was corroded and broke
 
RyanH said:
Had a truck do this once turned out to b going in and out of high idle. So i traced the wires from the coolant temp sensor and found one at the main engine harness was corroded and broke
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I'll give it a look for sure, this truck had several wiring issues so far, who's to say one more isn't lurking.
 
95-12valve said:
I'll give it a look for sure, this truck had several wiring issues so far, who's to say one more isn't lurking.
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Especially since you just did head gaskets then the problems happened, probly broke a bad wire from moving harnesses around.
 
When it does it unplug the coolant temp sensor and see what hapens. The idle will go way up, but see if the lope stops.
 
RyanH said:
Especially since you just did head gaskets then the problems happened, probly broke a bad wire from moving harnesses around.
Click to expand...

I had two GM tech friends go through it because I couldn't find the wiring issues, they found a couple along with the oil sensor and repaired them, pretty much went through the whole engine harness tested about every wire.
 
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