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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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  #1  
Old 03-29-2007, 08:29 AM
Horse_gal_jen Horse_gal_jen is offline
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Default Fuel pump in Duramax - more detailed description of problem now...

Going to edit this sicne I now have more info on the problem that might help....

so I started my truck a few days ago and was sitting there with it in park, then it stalled for no aparent reason and would not restart.

This happened once before and I changed the fuel filter and it started and ran fine from then on. we just had the injectors changed in December and we figured that was what had caused the earlier problem.

so i changed the fuel filter again hoping it would help, once I changed the fuel filter if I prime it it will run until about half the fuel is out of the filter then stall.

We had it towed to a garage and they checked the injectors and injection pump and all is fine.

There are no warning lights or gages on at all.

if you prime it and start it then hold you fut on the throttle it stays running until you let off.

While holding the throttle open the spedometer bobbles slightly but everything else looks normal.

The garage wont look at it unless I allow them at least 4 hours diagnosis time which is extremely costly. so we are going to bring it hoem and see waht we can rule out first to at least save some time and hopefully find the problem ourselves.
any suggestions on where to look would be helpful.

Thanks
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Last edited by Horse_gal_jen; 03-29-2007 at 11:29 AM.
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  #2  
Old 03-29-2007, 09:57 AM
DmaxMaverick DmaxMaverick is offline
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Your putz mechanic is correct. You don't have a fuel lift pump. The high pressure fuel pump (supplies the high pressure to the fuel rail) has a low pressure suction pump, that draws fuel from the tank. The entire fuel supply system is suction from the tank to the pump.

I suspect you have a leak between the tank and filter assy. Most likely causes are:

-Poorly sealed filter element (O-ring slipped during install)

-Center seal wasn't removed during the last install. This prevents the O-ring from making contact with the housing. The center seal is the rubber grommet that presses into the center/top hole of the filter element, and seals the center nipple in the housing. With the filter removed, there should be no rubber on the nipple (metal tube only, to the base). The seal should be installed attached to the new filter. A little lube on the inside of the seal will ease installation.

-Primer pump plunger. Is there a grimey mess or fuel around the plunger?

-Leaking/loose fuel line connection between the tank sender and filter assy.

-Cracked/broken fuel line between the fuel tank sender and filter assy.

-Failed fuel tank sender (fuel pick-up). A corroded or broken section of the tubing will allow air to be sucked from the tank, instead of fuel. Symptoms usually include no problem at full tank, but air leakage at a specific fuel level.

The most common cause is a poorly installed filter element. The O-ring needs to be fully seated in the groove and well greased/lubricated, or it will squeeze out of the groove during tightening. Dielectric grease of heavy axle lube (what I use) will help to seal it well. DO NOT prefill the filter (except in emergency, like a gelled system). Use the primer pump to fill it once it is installed.
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  #3  
Old 03-29-2007, 11:07 AM
SoTxPollock SoTxPollock is offline
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As Forest Gump would say stupid is as stupid does.
Your truck does not have a conventional fuel supply pump like a gas motor does. The injection pump pulls the fuel from the tank under vaccuum.
That being said, try taking the fuel cap off of the fuel tank and leave it off, pump the primer and start the engine. If it continues to run and does not die like it did before. You need a new fuel cap. Now that may sound stupid, but if the vent in the cap isn't working it will now let air flow into the tank as the pump pulls fuel out of the tank and it will not run without that fuel.
Good Luck. Let us know if that worked.
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Old 03-29-2007, 11:10 AM
Horse_gal_jen Horse_gal_jen is offline
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I was told that there is a lift pump that runs off the engine crank...is this correct?

We suspected as well that it might be getting air somewhere.

I just talked to another mechanic and he says he thinks a line is rusted by the fuel tank.

So we are going to drop the fuel tank and take a look.

Would a problem with air make any lights come on in the dash?

because there are no engine lights on whatsoever.

we did put a new fuel filter on before we had it towed to see if that was the problem but it didn't help.

should we try changing the filter again or checking the o ring?

I also heard that the fuel filter heads can go too?

thanks for the help...
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  #5  
Old 03-29-2007, 11:16 AM
SoTxPollock SoTxPollock is offline
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There is no lift pump at all from the factory. Only the injection pump is needed unless your racing it at the strip or pulling sleds at the truck and tractor pulls.
The key is everything has to be sealed against any air leak in the fuel system.
The only place air should enter in is at the filler cap where you fuel up. Be sure and ask them to try that before they go dropping the tank to get to some supposed rusted line. Thats gonna be costly. I've not heard anyone else talk about rusted fuel lines here.
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  #6  
Old 03-29-2007, 11:18 AM
Horse_gal_jen Horse_gal_jen is offline
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-Leaking/loose fuel line connection between the tank sender and filter assy.

-Cracked/broken fuel line between the fuel tank sender and filter assy.


what is the best way to look for a leaking or cracked line?


SO - It was the garage that told me they thought it was a rusted line.
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  #7  
Old 03-29-2007, 11:22 AM
Horse_gal_jen Horse_gal_jen is offline
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SO here's my plan of attack: any sugestions?

We will take the fuel cap off and try that first.

Then I read on another thread that it could be the fuel filter head so waht is the best way to check that?

The garage has already checked the injection pump and injectors (they were replaced 2 months ago) and all is fine.

then if that turns up nothing then we will check all the lines.
Any other suggestions are welcome.

and for the record I am not doing the work, my uncle and husband are sicne they are the ones who know more about this than me, I am just trying to get as much info as possible.
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  #8  
Old 03-29-2007, 01:45 PM
DmaxMaverick DmaxMaverick is offline
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Another approach is the sacrificial fuel cap. You use a fuel cap to mod a pressure cap by installing a tire valve into it. With this, you can pressurize the system via the cap with LOW PRESSURE (<8 psi) shop air. If there is a leak after the tank, it will leak fuel externally and lose pressure. If the leak is inside the tank, it will hold pressure and not leak externally.

There is a procedure describing this in a forum thread, as well as an article, but I don't have the time to dig it up right now. Someone else "in the know" will have to help if you can't find it.
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Last edited by DmaxMaverick; 03-29-2007 at 08:02 PM.
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  #9  
Old 03-29-2007, 03:16 PM
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JohnC JohnC is offline
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Quote:
Originally Posted by DmaxMaverick
... you can pressurize the system via the cap with LOW PRESSURE (>8 psi) shop air....
No doubt a typo... I'm sure he meant "<8" (less than) rather than ">8" (greater than). Regardless, I urge EXTREEM caution here. Typically, fuel tanks are not tested beyond 2-3 psi.
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Old 03-29-2007, 08:14 PM
DmaxMaverick DmaxMaverick is offline
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Quote:
Originally Posted by JohnC
No doubt a typo... I'm sure he meant "<8" (less than) rather than ">8" (greater than). Regardless, I urge EXTREEM caution here. Typically, fuel tanks are not tested beyond 2-3 psi.
THANKS JOHN!! Typo (edited).

I've tested mine and others up to 10 PSI, but recommend less than 8. I suggest gradually increasing the pressure up to the leak, or 8, which ever comes first. I know of several ocasions where dents were removed from metal fuel tanks with up to 30 PSI, but I wouldn't do it with a plastic tank. Many leaks, however, will show at lower pressure. I previously recommended less than 5 PSI, but since have located leaks above that.
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