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Old 08-15-2007, 11:37 PM   #1 (permalink)
DmaxProf
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Air leak in fuel system?

Today the temp was about 104 degrees. My wife left the engine running, she had our dog with her, for about 15 minutes while she went into a store. When she tried to pull out into traffic, she said it seemed like the truck had no power and did not respond to the throttle. She managed to baby it home and shut it off. After she reported her experience to me, I went out and discovered that I could pump the fuel filter fairly easily. After pumping it until it was difficult to push down, I started it up and it drove normally.

My question is: Should I be able to pump the fuel filter easily or should it be difficult as it is after bleeding the air when changing the filter? This afternoon the fuel filter continued to be fairly easy to pump. However, the truck cranked and ran fine. Do I have an air leak in the system or is everything working normally?
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Old 08-16-2007, 12:17 AM   #2 (permalink)
bigd4me2
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[quote=DmaxProf;1943683;]Today the temp was about 104 degrees. My wife left the engine running, she had our dog with her, for about 15 minutes while she went into a store. When she tried to pull out into traffic, she said it seemed like the truck had no power and did not respond to the throttle. She managed to baby it home and shut it off. After she reported her experience to me, I went out and discovered that I could pump the fuel filter fairly easily. After pumping it until it was difficult to push down, I started it up and it drove normally.

My question is: Should I be able to pump the fuel filter easily or should it be difficult as it is after bleeding the air when changing the filter? This afternoon the fuel filter continued to be fairly easy to pump. However, the truck cranked and ran fine. Do I have an air leak in the system or is everything working normally?[/quote

well,i can pump mine a couple of times when i have checked it.never checked because of a problem.only did it as you did.i don't think that in its self is a problem,but we shall hear what other members have to say.
but i say no problem,its not like priming a new filter.thats rock hard like viagra not that i tried it.
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Old 08-22-2007, 06:10 PM   #3 (permalink)
bigd4me2
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i'm giving you a bump to the top of the list,since nobody else has a reply.have you had any more problems since?hope not.
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2002 3500 drw sliverado dmax 4x4 4dr,afe stage 2 pr 7, ppe xcelerator, ppe boost valve, magnaflow exhaust,some gauges
2000 f350 srw standard cab 7.3 Afe stg 2 pr7,ats 4 in turbo housing,bdp 1 in exhaust housing,aih delete,bbha wastegate,D.I. regulated return,hx crossover,4 in turbo back magnaflow,dptuner 40tow,80econo,120race
01 gsxr 1000 knee grinder 10 flat 1/4 147mph
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Old 08-22-2007, 08:11 PM   #4 (permalink)
Los Lobos
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I would have to say there is more to it than a fuel related issue with what you're saying. Is there anyway you can have your codes read to see if you threw a code that reset after sitting? It will be in the history. The problem sounds like a fault code or a tranny code with defuel. Check those and let us know what you find.
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Old 08-22-2007, 09:00 PM   #5 (permalink)
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[quote=bigd4me2;1943785;][quote=DmaxProf;1943683;] My question is: Should I be able to pump the fuel filter easily or should it be difficult as it is after bleeding the air when changing the filter? This afternoon the fuel filter continued to be fairly easy to pump. However, the truck cranked and ran fine. Do I have an air leak in the system or is everything working normally?[/quote

The stock fuel system for the Duramax has no lift pump to pressurize the fuel system. The only thing moving fuel through the system is the vacuum developed by the injector pump. The only time this system is pressurized is when manually pumping. Any other time the system is under vacuum.

The fuel filter assembly has the manual hand pump, which is used to prime system from the tank to the filter. When priming the system, you open the vent on filter assembly, and start to pump. Depressing pump down pushes air to the vented filter. As the pump rises, the vacuum developed sucks fuel from tank. You continue pumping until you suck enough fuel to overfill filter, and now fuel exits vent.
Now if you close vent fitting, and continue to pump, you pressurize the filter to the injector pump. If any small amount of air was in injector suction line, it will compress. When engine is started the first time, if there was a small amount of air, the motor might hick-up, but will probably continue to run, and all air is gone. Now with truck running, the fuel system will go back to a vacuum.
Per info I read on the Baldwin site some time back, it is typical with a vacuum fuel system that the dirty side of the fuel filter will only be about 1/3 full. That is why if you cut open a dirty filter, usually only the bottem 1/3 to 1/2 will be black, and the upper only brownish.
After shutdown, with the dirty side of filter only 1/3 full, the gas area above fuel will be compressible if the hand pump is operated.
Sorry for long post.
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