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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

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Old 07-09-2019, 05:38 PM
Pfouts1001 Pfouts1001 is offline
Join Date: Dec 2004
Location: Ohio
Posts: 6
Default 2002 LB7 Fuel system issues P0087

I Have a 2002 2500HD LB7/allison with about 175K mi. Everything with the truck is bone stock. The injectors were replaced at about 120K. No lift pump, but on the list of things to do esp now.

Last fall, I took the truck on a 1600 mile trip. Going out with a empty 5000lb enclosed trailer the truck ran well but got horrible mileage. I attributed it to a stiff head wind. Coming home loaded - 10000lb trailer, the mileage was much better with a tail wind. Again I figured it was the wind, and it may have been.

Fast forward to the spring, the truck had been in storage since December, and not driven since the above mentioned trip. The truck started good. I idled it to warm up for a few mins. When I pulled out on the road, the truck had almost no power above 1500 RPM. Down the road a few miles the CEL came on. I assumed maybe I had some bad fuel, or the fuel filter had water, or had gelled over the winter. I turned around and went back to the shop. Checked codes - P0087. I humored myself and changed the fuel filter - no change.

I checked the fuel lines from the tank to the filter head. No kinks, no bulges. Fuel flows easily and fast using the primer pump. I replaced the filter head since I found a good deal on one, and it was suspect to me. This made no difference. I checked oil level and condition. Oil is right on full as it always is, is clean looking after the above mentioned trip, and has no evidence of fuel contamination. I installed a clear line on the output side of the fuel filter - shows no evidence of air. I replaced all rubber lines and clamps coming to and from the fuel filter.

I borrowed a friend's techII. Rail pressure showed around 4600lb at idle, when max pressure was commanded, I could only get around 8500Psi. Balance test, which I don't know how much merit I put into based on the low pressures, showed one injector at +4, all of the others were within +/-2 range.

I did the bottle test on the FPRV, and was able to get some bubbles, so I replaced it. This made no difference in pressures, or the performance. I also humored myself and swapped a known good fuel pressure regulator. This made no difference in pressure or performance. While road testing after the regulator swap, the truck shut off going down the road and I have not been able to start since.

Since this happened, I tested the return with pump and injectors separated and relay pulled. After tons and tons of cranking, I was unable to get any return from the injectors. I was able to get some return from the pump, so i started with an empty container and only got about 30ml in 15 seconds of cranking. I also tested pressure and vacuum using a gauge in the test port inline going to the pump. Pump only pulls about 1in/hg. This bleeds down to zero in about 10 mins. I also tested using the hand primer to pump up to 10Psi. This drops to 8 Psi in about 1 min 30 seconds and drops to about 1 psi in 6 hours. I tried starting at 8 Psi with no start.

I have also checked rail pressure with the techII since the truck does not start. I can not remember the pressures (probably my state of pissed off at this point) and cranking resulted in VERY minimal rise above a non cranking state.

I am thinking my pump is shot, but I just wanted to be sure before I did it. If anyone else has any suggestions, I'd be glad to listen.

2002 GMC 2500HD CC/SB 4x4 D/A<br /><br />\"The Duramax Diesel Knows how to be livin\'....Just keep the wheels spinnin\' and the beavers grinnin\'!\"

Last edited by Pfouts1001; 07-09-2019 at 05:44 PM. Reason: added information
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Old 07-10-2019, 09:14 AM
Kennedy Kennedy is offline
Long Distance Crew Chief for BMDMAX
Join Date: Mar 2000
Location: Loyal WI US
Posts: 10,674

Originally Posted by Pfouts1001 View Post
No lift pump

Checked codes - P0087. I humored myself and changed the fuel filter - no change.

I did the bottle test on the FPRV,

Start with the lift pump. You needed this 17 years ago. Email me and I'll provide recommendations including filtration and treatment. Lack of these is likely at the root of your problem.

Measure supply side restriction with this:

Bottle test is a waste or time on the LB7. The relief valve is VERY robust and pretty much never fails. They used to fail when guys were doing the old pressure fooler boxes, but that was 15+ years ago now.
Kennedy Diesel-owner
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Old Today, 12:25 PM
DieselRick87 DieselRick87 is online now
Join Date: Jul 2019
Location: Lincoln
Posts: 2

Im.having the same problem. I changed the fpr and the code went away hoe ever I am still lope at idle and hazing after warmed up. Ballance rates are all good. Ran some trans fluid in the fuel hope this cleans up some stuff. Also want to change the fuel filter after I run the gas low enough. Runs like a raped ape tho. Just wish I could figure the rest out
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Old Today, 12:31 PM
DieselRick87 DieselRick87 is online now
Join Date: Jul 2019
Location: Lincoln
Posts: 2

My rail pressure and desired rail pressure are all dead on.
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