Truck surging at idle after installing new FPR

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Whipper Snapper

New member
Mar 24, 2015
9
0
0
Ok, update! Today I installed a 5.5-9 psi fuel pump to try and see if it takes away the loping, and it did! Hooked it up to the inlet of the fuel filter housing and turned it on and started the truck and no loping. I then put it back to factory and the loping came back. Any ideas to why this is happening and what is the correct cure, Air Dog or CP3?

Remember the desired fuel rail pressure and actual are almost dead on at all times.
 
chevyburnout1

chevyburnout1

Fixing it till it breaks
Aug 25, 2008
2,368
1
38
Berthoud, CO
Sounds like it's sucking air when you don't have the lift pump on. I understand you rebuilt the filter head and did the funnel test but there are still three rubber hoses between the FICM and injection pump. Under vacuum they could let air in. Air in the line can definitely cause a funky surge in fuel pressure. Some scanners aren't fast enough to catch the pressure jump.
 
Stancedlb7

Stancedlb7

Cummin Stroke this Duramax
Feb 9, 2015
649
0
0
SLC, UTAH
chevyburnout1 said:
Sounds like it's sucking air when you don't have the lift pump on. I understand you rebuilt the filter head and did the funnel test but there are still three rubber hoses between the FICM and injection pump. Under vacuum they could let air in. Air in the line can definitely cause a funky surge in fuel pressure. Some scanners aren't fast enough to catch the pressure jump.
Click to expand...

X2 The lift pump will help but you'll end up with a fuel leak down the road. And a valley fire will destroy your truck.
 
C

Cattractor

New member
Apr 19, 2016
3
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0
Same issue to the T

I have an 01' LB7. It has a loping idle. It's the worst when cold. Originally it would smooth out when warm. Now it's consistent at idle. It will smooth out when I pump up the hand primer. I replaced the FPR twice. Still same issue. My injectors were not the best on the ballance rates. So I pulled them and had them tested. 2 were bad, all 8 failed the leak down test. I replaced the injectors. I've replaced all Fuel lines to pump. Still loping at idle. I installed a transfer pump. It helps but does not completely eliminate the issue. I've also checked wiring to FPR. It's ok. Checked engine with a snap-on scan tool all values good except the actual fuel pressure jumps around the desired as it lopes.

I have yet to replace the CP3...
 
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