Weak CP3

[Caleblgarr]

Hey everyone. I’m new here and hope to find some answers to my questions. I have a ‘05 GMC Sierra 2500HD 4x4 CCSB LLY with delete, bigger turbo mouthpiece, up pipe, down pipe. I just replaced the FPR for the 3rd time. It starts up and idles great. When I take it down the road it won’t go over 2500RPM. It’s in limp mode for some reason. I keep getting P0089 and P0090 and I’ve changed the wiring connector and FPR 3 times now. My balance rates are all within spec but my fuel rail pressure won’t go over 10k when driving. But will bounce between 8k and 24k at idle. What’s going on with this thing? Thanks for the help.


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[KyleC4]

If it’s bouncing between 8k and 24k at idle, I would look at fuel rail pressure sensor. Does the idle sound of the engine change when it’s bouncing around ?

 

[Caleblgarr]

It just sounds like a miss. At first it sounded like a super cammed duramax. After it clears up some it just sounds like a miss. I thought about that possibly being the issue. Is there any way to check the sensor?


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[Bdsankey]

A weak pump wouldn't be the culprit for rail pressure bouncing at low load/idle, that would point me towards an FPR or high lift pump pressure.

 

[Caleblgarr]

Well I’ve changed the FPR 3 times with each regulator increasing in price. I’m running out of ideas here. I don’t wanna dump thousands into the fuel system if it’s just one part that needs replaced. It’s got a new filter on it too.


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[Bdsankey]

What brand FPR are you using?

 

[Caleblgarr]

The one I have in now is an Exergy FPR.


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[Bdsankey]

What are the modifications done to the truck?

 

[Caleblgarr]

EGR delete, cold air intake, turbo mouthpiece, up pipe, down pipe, 4” exhaust. No tuner to disable EGR DTC’s.


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[JoshH]

Does the truck have a lift pump? If yes, what is the pressure being supplied to the CP3? If no, how much vacuum are you seeing at the test port next to the alternator?

 

[dndj]

Possibly a flaky fuel pressure sensor? The ECM reads the output of this sensor to command the FPR to command the desired value.

However, a P0090 would say probably not. P0090 sets when the control current from the ECM to the FPR is outside of the range between 50mA and 1600mA. Check for shorts to ground/+12v and intermittent connections from the ECM to the FPR.