LBZ: surging NOT FPR

[Mpsoldier]

2006 170k built trans lift pump stock injectors ppei tuning.
ZERO CODES
new fpr Gm even swapped again maybe bad out of box no change
new rail pressure sensor ( original problem) fuel pressure stuck at max rail..

actual vs desired i can see it drop in rail when it does its surging usually after 2k rpms.
balance rates are nothing crazy +/- 1.7
calculated fuel rate you can see jump from 9-18
sounds like a fuel knock but doesn't do it all the time.
isolated fuel system thinking maybe cracked pickup still same.
isolated every injector capped off at rail still pops and miss.
disconnected maf thinking maybe scale is off.
jumped out motor to grounds and chassis to ground jumper cables maybe bad grounds no change.

sounds like a fuel issue but don't want to through more injectors at it when nothing i do isolating them changes the problem.

ideas?

doing return rate test now but don't think from everything else i have tried its going to show anything.

was thinking maybe crank or cam sensor but wouldn't code exist? was thinking electrical but then again no open circuits no codes for them. fuel pressure sensor is seeing 5.0v no broken or bent pins in ecm or harness double checked those.

 

[rfletes79]

Lift pump pressure to high?

I currently have this issue with my chevelle, switched to a 10MM pump and it is not happy with my lift pump pressure, makes actual rail extremely high at idle, knocking like crazy. When I turn off the lift pump, pressure goes to desired, and sounds 100% normal.

 

[Mpsoldier]

Does it even when lift pump is unplugged it's sitting at 8psi anyway

 

[2004LB7]

Could be can or crank sensor. That can cause some weird stuff.

Can you get any logs?

 

[02greysixer]

My lly did some weird stuff like that when the crank sensor was failing. Pop, miss, surge, etc. It didn't set a crank code until it finally just wouldn't run anymore.

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[Mpsoldier]

I may just replace cam and crank sensor for the hell of it

 

[Mpsoldier]

Could be can or crank sensor. That can cause some weird stuff.

Can you get any logs?

Yeah and the only thing abnormal is the drop in rail or spike in rail when it starts popping and missing. But nothing that's given me anything to go off of.

 

[Chevy1925]

Put the stock tune back in. See if it still does it

 

[Mpsoldier]

Put the stock tune back in. See if it still does it

Does it On stock tunes as well

 

[Chevy1925]

Fuel temp, coolant temp, and baro check out ok?

 

[Mpsoldier]

Fuel temp, coolant temp, and baro check out ok?

Coolant temp is maybe 5 degrees off from ambient
Fuel temp within 3 degrees of coolant temp on start up
Bark voltage is 3.9 at 14.2psi seems to be spot on for me.
Cam refer pulse missed is 35 thought this was suppose to be zero but crossed over to my other lbz is at 36

 

[Mpsoldier]

This truck is going to be the death of me. New injectors no change compression test reads good 340 across board. Guess change out the engine harness is my next thing. No codes sucks. Worse part is this truck is rusty

 

[JRein]

Not sure if you've looked into it but just going back to basics, how's the filters. I'm not sure if you've gone through a whole tank since doing injectors or how long it took but maybe bad fuel. Bio diesel, if you happen to use it, is quite hygroscopic compared to regular diesel. I'm sure you've probably eliminated these but I've seen some seasoned technicians troubleshoot generators and such for a good amount of time trying to figure out why it's not holding a load. Come to find out it's a defective fuel gauge or some asshat wired it backwards. Good luck

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[Yellow Jacket]

I just fought a LB7 for a week, it was the ECM...the driver in the ECM must not have been able to maintain a steady Output signal...

 

[Mpsoldier]

I just fought a LB7 for a week, it was the ECM...the driver in the ECM must not have been able to maintain a steady Output signal...

This is my next thing grabbing one off my lbz to try. Cutting open engine harness now see if I see anything again. But same symptoms no matter what I change

 

[radvans]

I'd the surge bad at high rpm? My lb7 ran fine if I drive East but surged under hard acceleration. Ended up being the cp3.

 

[stibuilder]

Having the same issue its just on #8 knocking replaced all the things the OP did, even the engine harness.

 

[Mpsoldier]

Just injector swap out with another cylinder

 

[stibuilder]

Oh yeah it stayed on #8 no matter what we do. Always #8 new injectors i think its the head, valve not sealing or something at this point.

 

[Yellow Jacket]

Compression check it