LLY: LLY loping at idle

[sterlinLBZ]

I have a buddy that just bought a 04.5 lly with 120,xxx miles. as sclean as can be inside and out!But in 05 it had water damage and the car fax and the preacher he bought it from (Id hope he wouldnt lie about it:thumb said everything was replaced at a GM dealer with all new GM parts under warranty and i would think after 8 years somthin else would have shown up if there was a still a problem. But now its starting to lope and surge some at idle. truck has been bone stock for its whole life except for a 4" exhaust and now a ppe programmer. any clue what causes this? i know the fuel pressure regulator but wanting to know more and the best way to check to find other causes.

 

[TLyons90]

Any idea when the last time the fuel filter was changed?? That is where I would start...

 

[tracas7]

My LLY does the same thing. After a long drive like a hour or so and I come to a stop it will start loping. Don't know why.

 

[05chevy]

I'd say fpr. Fuel pressure regulator going bad.

 

[dirty_max]

fpr would be my guess as well. as long as the fuel filter is good.

 

[ss600hp]

my truck does the same thing, 205000 miles on it now, also heard that the fuel regulator is the cause, mine is still stock. I also read that an increase in supply fuel pressure to the regulator will cause this as well, such as an airdog fuel filter/pump, but that can be corrected in EFI tuning. I would also like to know if this is factual or not...

 

[slipclutchms]

It can be.... But you can just turn down the lift pump pressure till it stops pushing thru the regulator.

 

[sterlinLBZ]

Thanks guys, if I unplug the sensor will it make a change in the idle so we will know if thats the problem or not?

 

[00f3fiddy]

Mine loped until I put the air dog on. It stopped after that. Running 12 psi too!

 

[Harbin_22]

If you unplug the FPR, it will max out the rail pressure and sound pretty rough. Not really going to tell you if that is the problem, but it probably is bad

 

[Cknight199]

Mine loped until I put the air dog on. It stopped after that. Running 12 psi too!

X2 lift pumps pushing out too much psi will cause the truck to lope under certain conditions.

 

[00f3fiddy]

X2 lift pumps pushing out too much psi will cause the truck to lope under certain conditions.

I'm saying mine quit loping after I installed the lift pump!

 

[Cknight199]

I'm saying mine quit loping after I installed the lift pump!

Ohh gotcha, I have heard that higher psi on a lift pump will cause loping at idle though.

 

[sterlinLBZ]

Yea I know my lbz would when I was adjusting my air dog, but this truck doesn't have any kind of lift pump or pusher on it