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Duramax LB7 loosing prime

JEFFRPM

Non Sugar Coated
OK the world just came to an end I wait for it.................I bought a duramax yea I know the earth may have just went off its axis but I couldn't refuse it was CHEEP 2003 xcab shortbed 2WD with a paltry 76000 miles so I lowered it chipped, intercooler, injectors, you get the drill fun as hell 24mpg hwy 6200lb go cart, here's the problem I installed a extreme diesel products fuel filter adaptor so I can use the CAT 2micron fuel filters (I hear that's why injectors die on these things) well after every trick in the book from replacing all the Orings in the stock filter mount to both hoses to & from the filter body it still looses it's prime after sitting more than a half hour causing me to pop the hood pump away on the bleeder pump to burp the fuel system and it runs great full power no driveability issues whatsoever park it for half hour or so and it will not start burp the system walla it runs perfectly, hell I've even replaced the CAT filter with a donaldson 3 micron same story pump it up before starting it does it hot or cold it's even learned to introduce air in the fuel system SITTING meaning I pump it up don't start it after half an hour it won't start I'm completely lost I guess the adapter is bad I'm afraid to pressurize the fuel tank to force a fuel leak except the fuel goes through the ECM on the suction suction side and I'm pretty Shure the "magic box" doesent like to be pressurized HELP!!!
 

Chris Tobin

Well-Known Member
Maybe a seal or O-ring was bad or twisted when you rebuilt the filter head, or maybe you missed a seal. I'd suggest buying one of the Viton O-ring kits from Merchant Automotive or dmaxcentral.com. And then rebuild the head completely. A lot of the guys run the CAT filters so I doubt it is the issue, but I suppose there could be a leak in the adaptor. You can also replace the bleeder screw with a billet one from MA as the plastic one can cause problems...

Duramax Filter Head Rebuild Kit, 2001-2010 Duramax

MA is a GREAT source for all Duramax and Allison parts!!!

My LB7 was loosing prime too and we rebuilt the filter head and it was great from there. Then we installed an AirDog filter system and deleted the factory filter and it is good to go from there...

They are great trucks and can run darn near forever... Mine had 353,XXX miles and blown headgaskets when we bought it... Then new headgaskets and a bunch of bolt-on parts and we are making about 550/1000 HP/TQ and it runs great!!! Very fun truck!!!

Let me know if you have any other questions, I'll be happy to help.
 

duramaxnate

New Member
Sounds like a defective filter housing. I have seen trucks come through my shop that have had this issue. Pm me if you need anything. Or call my shop RIVCO Motorsports 951-817-7685. All I work on is duramaxs..

Sent from my XT1650 using Tapatalk
 

JEFFRPM

Non Sugar Coated
Ding ding ding we have a winner! It was the factory filter mount after pinching off both lines on the ECM, then boring a couple of holes in one of the dogs tennis balls placing said tennis ball on filler neck (after removing fuel cap) applying VERY little air pressure to the entire fuel system the cast aluminum factory filter mount hemmoraged fuel from a miniscule Crack that you can't see at all PROBLEM FOUND replaced it and no more having to pop the hood everytime you start it. BTW the plastic fuel tank really hates being pressurised it popped, banged, bitched the entire time, I'll bet thier wasn't 00.2 psi placed in it so be very carefull attempting this stunt. Tobin your right merchant automotive is the only place I buy special application parts from.
Another thing when replacing the mount buy one for a top kick medium duty truck it has banjo fittings allowing you to clock the lines anyway you want verses the pickup truck version that comes with the POS pressed in pre clocked hose fittings and it's about $170 bucks cheeper hehehe. Here's a picture of what I call the "atom smasher" the Hybrid logos came from amazon just to shut up the daughter I couldn't find gluten free ones.
 

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JEFFRPM

Non Sugar Coated
After talking talking to one of my buddy's who runs the maintenance on the union pacific railroad track support vehicles told me the CAT 2 micron filter is great for the duramax EXCEPT now thiers is no filter with a water/drain on my truck and he's correct because when I deleted the oem filter it had a water in fuel sender (that he says never works) in the bottom of the oem filter with a drain petcock you could periodically drain a little bit of fuel & water out of the oem filter (that BTW also fails) making shure you never have water in the fuel system aiding in the life of your injectors and injection pump, well mines now in the dumpster soo he told me about this place in Oregon called dieselfuelfilterkits.com said I needed to purchase a water filter with lift pump that goes inside the frame rail on the tank side of the truck after the tank and before the CAT filter it comes complete with mounting plate, pump, Baldwin watertrap/filter and all hoses & wires, I questioned him about the pump thing he stated it pushes the fuel through the 2 micron CAT filter instead of the stock fuel pump sucking fuel 10' to the CAT fuel filter that's really not supposed to be used in a suction situation in the first place ok that makes sense (sorry about the novel) ok I bit, purchased one and just finished installing it, Well guess what anyone if you owners of these 2001-2011duramax powered things need to get one because I thought my truck ran perfectly (it did) now it's a completely diffrent truck it starts by just breathing on the key not that it started bad before you just touch the key it starts now it idles better and the off idle throttle responce is neck breaking WTF? It just flat runs better than it ever had not that it dident run like a bat outta hell before. The problem is inherently built in every GM truck with a duramax, The engines were never designed to suck fuel PERIOD all of them are hurting for fuel that's another reason these things eat injectors lack of air free fuel and a oem fuel filter that can barely stop low flying geese. I asked about this airdog filter system that's the rage he says there's nothing wrong with them at all EXCEPT they hang down below the frame in the way of everything you go over thier expensive as hell and unless your running a compound turbo setup with over 1800 ft lbs of torque at 6000rpm and need to have cool fuel temps by recurculating the fuel at a very high rate there a waste of money you will never need one. Gawd that was a long explanation sorry.
 

Chris Tobin

Well-Known Member
Jeff,

That is why many diesel owners buy a FASS or AirDog lift pump/filter combination for their truck, there are also now ones from Aeromotive and a few other manufacturers as well but the FASS and AirDog are the most popular ones. They incorporate a lift pump as well as a 2micron filter and water separator and also remove entrained air from the fuel...

With my 01 Duramax truck I am running an AirDog pump/filter assembly on the framerail and have deleted the factory filter assembly completely.
 

JEFFRPM

Non Sugar Coated
What kind of skid plate you running? That airdog things huge and sticks way to far down below the frame for my lowered ride, hell if i had to use one of those things in a off road/chase truck I'd be one nervous mofo or at least have many spare filters because of the chance of ripping them off yes there a great system but DAMN.

The Atom smasher (that's what I've named it) only has 6" clearance from the ground to the factory transmission crossmember and I only dropped it 3" front and 6" back the tires are 0.500 taller than stock ones so thiers no way for me to run one of the airdog systems.
20170804_171531.jpg
 

Chris Tobin

Well-Known Member
What kind of skid plate you running? That airdog things huge and sticks way to far down below the frame for my lowered ride, hell if i had to use one of those things in a off road/chase truck I'd be one nervous mofo or at least have many spare filters because of the chance of ripping them off yes there a great system but DAMN.

The Atom smasher (that's what I've named it) only has 6" clearance from the ground to the factory transmission crossmember and I only dropped it 3" front and 6" back the tires are 0.500 taller than stock ones so thiers no way for me to run one of the airdog systems.View attachment 183685
Nice looking truck! We installed my AirDog VERY tight to the body and as high up on the frame as possible and it does not hang down below the frame at all. I was concerned about that too, but we have done some rock crawling with the big truck and haven't had a problem at all...

Longhorn Fab makes a nice skid plate for the AirDog.

I believe the filters on the FASS may hang down a little lower than the ADs...
 
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