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Discussion Starter #1
ok, i have posted here on the 911 on this problem.
i took the advice and told the owner to get the shim kit, since he had used a programer to up the power when towing and also helped the economy.
but this truck has been dong this for 2 years. it only happens when towing, and when weather gets warmer.
after driving for awhile it will fall on its face when you try and get some accelleration above 2000 rpm. it stumbles, and feels like there is a lack of fuel. it gets a check engine light. the code is low fuel rail pressure.
the owner has put 2 shims in to start. still acted up, so he added the third one. it is still acting up.
it is not the fuel filter.

he is getting upset, since he has taken it to a dealer for the problem and they said it was the filter, but it would act up just a few miles out.

funny thing is he has another 07, and it is programmed the same way and has not ever acted up.

any ideas would be helpful.

also, if anyone has had this problem please tell how you got it fixed.
oh, to add, this is when we tow trailers with it.
with out trailers on, no problem.

also it gets worse when the a/c is on also.

:help
 

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Discussion Starter #3
would you be talking about the fuel pump going bad?
how can we test it?
or would it have to go to a dealer to test the pressure?
 

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Maybe you should get a lift pump...Idk but thats just a thought
Good Luck
 

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Discussion Starter #5
i am hoping the owner will check out the posts i haev made and let him decide what to do.
on another post i made a while back, they mentioned the cp3 pump could be weak.

too bad i could not use a holly fuel pump to boost up the pressure.
 

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I'd recommend a lift pump as well. But don't get a heap holly pump, get one with diesel specific seals. That should help :)

-Jesse
 

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Discussion Starter #7
here is what i do not get, he has 2 other 07 trucks, same engine, the 1 ton standard cab has had no problems at all. his 1 ton crew cab model went into limp mode, he did the shim kit to it and no more problems with it. the 07 3/4 ton gmc is the only one that is giving us fits.

but i will pass this info along.
 

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Discussion Starter #8
well i had to drive the 07 3/4 ton today. we had a fifth wheel on it and it just acted terrible. we had to put a travel trailer on it which is lighter, to get the truck to stay moving.
now here is even worse news, the bosses 07 1 ton crew cab has started acting up too.
so he called me and he is removing the program from both trucks and going back too stock settings.
both trucks are picking a bad time to do this. he already lost the 04. it sucked the injector through, and now it needs another engine.

but when the trucks are pulling heavy loads, is when it gets real bad.
this is a bad time for 2 trucks to be down.
is there a simple or low cost fix?
 

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my 07 was doing the same thing underload or not i replaced 2 high pressure relief valves then i ended up changing the injection pump..after the pump it never went into limp mode again.. not cheap fix but it did fix all the problems...
 

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Discussion Starter #10 (Edited)
well that is what we are thinking now. both the 3/4 ton gmc and the 1 ton gmc crew cab, both '07s, are doing it. we even took out the program, and it did it still. even have tried with the tow/haul turned off, and still does it. so we have decided that the fuel pump is gone bad. sad part is we are down to 3 trucks, and we have gotten busy. the trucks have been running non stop. one group gets back and the other takes off.
 

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Hey tell the guy that ''owns'' the truck he needs a lift pump...If it is back to stock and still giving a fuel code then you have other issues.
 

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how many miles are on these trucks??I have never heard of 06 and 07's having fuel pump issues!
One thing to be sure of is where the fuel is sucked from out of the tank.There is mesh material over the down spout[in the tank],and if it gets clogged you will think your pump is going out......It is common on higher mileage trucks,and especially ones who have their fuel purchased at different stations often.Rule that out then look at the pump.A pump is awful expensive to just replace,I would check that first if they were mine though....just my 2 cents
 

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Discussion Starter #13
the 07 3/4 ton has 248000. the 07 1 ton crew has 147000.
the crew jsut started having this issue. we did the fprv shim kit. he put 2 shims in and it still did it. he added the third one and still does it on the 3/4 ton and 1 ton.
it is giving the low fuel rail pressure code.
now after the trucks got back, from pulling trailers, then we took off with out letting them cool down, and the 1 ton could not go over 2000 rpm. when we let them sit for about 5 minutes, then we can get over 2000 for awhile.
then it goes back into limp mode. we have to be careful not to exceed the 2000 rpm or we lose speed til we can ease it back up.
also when it does this, the primer can be pushed down about 3 times and then the pressure builds back up again and it will run good for awhile.
 

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fuel pressure leak somewhere?
 

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Discussion Starter #15
but there is no sign of fuel leaking.
i am thinking now that when pulling trailers, the engine requires more fuel, and the pump can not keep up.
it is sounding like as others have said, the cp3 is going out. it is possible for it to get weak and worn out. could also be just poor manufacturing for the makers of the pump.
 

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Discussion Starter #16
let me reupdate what has been done.
the 07 3/4 ton has been doing this for a year. and only does it when it is warm outside.
in teh winter it is fine. and only acts up when pulling a trailer. it has been to dealers and checked even when a trailer is on and they find nothing.
the 07 1 ton crew cab just started doing it a few months ago. the boss went to colorado with teh wedge trailer and cargos on it, and it went into limp.
both have had the shim kit put in, both have had the filters changed.

now here is another thing i haev found, when they go into limp and have the fault code of low fuel rail pressure, you can push on teh primer about up to 3 times to build pressure back up.
also i took cap off the 3/4 ton when it went into limp, and noticed some bubbles around the shrader valve..
now i have bled both units yesterday. when i pushed on primer while holding valve open, i did notice some air came out.

so now i am just waiting to hear if that helped.
if not, i do need a great suggestion, and hope it is simple.
someone told the other driver it could be electronic in nature. but i wonder.
i also have been told it could be the pump.
is there any diagnostic program that can be connected to a laptop and get a live test to find what is going on when the trucks are running to pin piont the problem.
 

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If it really comes down to it, I will be willing to meet you somewhere in between Galesburg and Yorkville IL and I can log it with EFI live.

It is a fuel limp and @ 2k rpm it automatically cuts out the fuel. The air bubbles are coming out of the priming button? or are they coming out of the bleeder screw?
 

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Discussion Starter #18
i sent you a PM. the bubbles are with engine off and are at the shrader valve where you connect a guage to check pressure. i believe it is for the rail. it is located behind the alternator. i am guessing that is where you bleed the rail.
i held the valve pin in while pressing on the primer.
the crazy thing is i would think when the engine has been running you could not push on the primer. but when it goes into limp, the 3/4 ton truck will not go over 1900 rpm now. and you can push on the primer.
now when i drove a semi, after teh engine ran, you could not push on the primer at all, but with this duramax i noticed that when it went into limp, you could push the primer up to 3 times to get pressure back into the lines and about a minute later you take off and it is fine for awhile.
the 1 ton crew cab has about 150000 and the 3/4 ton has 240000 miles. both are 07s and both are gmc. the 07 chevy which was a 1 ton never had the problem. it is now gone. it was wrecked. about 2 weeks ago.
 

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i sent you a PM. the bubbles are with engine off and are at the shrader valve where you connect a guage to check pressure. i believe it is for the rail. it is located behind the alternator. i am guessing that is where you bleed the rail.
i held the valve pin in while pressing on the primer.
the crazy thing is i would think when the engine has been running you could not push on the primer. but when it goes into limp, the 3/4 ton truck will not go over 1900 rpm now. and you can push on the primer.
now when i drove a semi, after teh engine ran, you could not push on the primer at all, but with this duramax i noticed that when it went into limp, you could push the primer up to 3 times to get pressure back into the lines and about a minute later you take off and it is fine for awhile.
the 1 ton crew cab has about 150000 and the 3/4 ton has 240000 miles. both are 07s and both are gmc. the 07 chevy which was a 1 ton never had the problem. it is now gone. it was wrecked. about 2 weeks ago.
if you pumped pressure back in like that then you DEFINITELY have either a leaky bleeder screw or air leak somewhere....Think you have a air leak somewhere and maybe the ECM trying to make up for it is giving problems??Go check to see if the CAC hoses are sucking air or leaking/not tight!
 

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Okay, Are you guys opening up the bleeder while pushing the primer? if there are air bubbles coming out of the fuel rail valve it sound like its not completely bleed, maybe a bad fuel filter housing gasket? or air coming in through the primer button or the bleeder screw!
 
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