# A Duramax mystery for ya'll



## firephil (Jul 11, 2006)

A while back I was pulling the bat boat and the Chevy laid down on me, very minimal power. 55 max by feathering up to it. Supposed to be the fuel pressure regulator so I had it replaced at the dealer. went about 3 months, no problem. Hooked up to the boat again and went 2 hrs then it did it again. Took it back and they replaced something else in the fuel train. Ran fine for 3 months. Hooked up to the boat again went about 5 miles and it did it again.
So my question is why do you think it would run fine with no trailer and some times 1000 pounds in the bed but I hook up the trailer and it loses most of the power, not really limp mode, but it will only ease up to about 50 mph. No trailer and it runs like a scalded cat. There is no tuning or mods on it.


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## RB II (Feb 26, 2009)

I am not a mechanic but understand that there is an issue with the oil pressure sensor on those trucks. Basically when pulling a load the oil thins, if/when the truck is kicked down quickly by disengaging the cruise control or stepping off of the throttle quickly the oil pressure sensor is set off and it goes into limp mode for a while.


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## Muleman (Dec 6, 2011)

What year model?????? Which engine LBZ, LBL ect?????


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## snapperlicious (Aug 11, 2009)

Any check engine lights come on? Filter new? Mass air sensor clean?


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## firephil (Jul 11, 2006)

01, new filter, not sure of mass air sensor


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## firephil (Jul 11, 2006)

No one has had this problem?


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## bigdav160 (Aug 25, 2004)

Yes, years ago I had a customer with the same complaint. Third visit he brings the trailer with him. We go for a test drive and a couple miles up the road one trailer tire blows out and the other has smoke coming out from the bearing :work:

We left the trailer on the side of the road and he never came back complaining about the low power from his truck.


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## firephil (Jul 11, 2006)

Ha Ha, I guess that would do it. My trailer is in good shape though


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## surf_ox (Jul 8, 2008)

Ok 8 replies and no "it's a Chevy" smart Alec comment

Great job refraining guys 

Try hooking up trailer without lights. Just load only unless it needs power.


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## artys_only (Mar 29, 2005)

Go to the Duramax forum they will be helpful their , I drive a duramax and never had an problem with the truck going into limp mode .


Transplanted from the North


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## JamesAggie (Jun 28, 2012)

Sounds like a fuel filter problem to me. Same thing on my dad's '03 ford 6.0. With no load drive like a champ. Hooked up to a 5th wheel trailer it did fine until rpms started to climb. We could get up to speed very slowly but when we hit a hill and it down shifted we had to baby it or it would bog down. No lights came on. Dealer said everything checked out. Dad and I put our minds together and realized the motor was starving for fuel. Replaced both fuel filters and that thing was a beast after. Filters had a red soot in it. Figured we got bad diesel somewhere.


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## snapperlicious (Aug 11, 2009)

*Yep*



JamesAggie said:


> Sounds like a fuel filter problem to me. Same thing on my dad's '03 ford 6.0. With no load drive like a champ. Hooked up to a 5th wheel trailer it did fine until rpms started to climb. We could get up to speed very slowly but when we hit a hill and it down shifted we had to baby it or it would bog down. No lights came on. Dealer said everything checked out. Dad and I put our minds together and realized the motor was starving for fuel. Replaced both fuel filters and that thing was a beast after. Filters had a red soot in it. Figured we got bad diesel somewhere.


Actually that just reminded me of my problem I had a few years ago. My truck won't take the metal autozone filters but will take the plastic ohreilly filter. Does the same thing you mash the gas and it loses power.


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## firephil (Jul 11, 2006)

It was the injectors


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## snapperlicious (Aug 11, 2009)

Care to elaborate? How did you find that out?


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## bonehead (Jan 25, 2009)

Check for fuel leaks around your filter. Mine did something like that . It was the o'rings on the heater inside the filter housing . Bought a rebuild kit for around 30 bucks. And fixed it myself


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## firephil (Jul 11, 2006)

I found out from the codes read at the dealer. Fuel pressure was dropping due to excess fuel being dumped back to the tank by the faulty injectors. I disputed it but they did it twice and that is what the tech came up with. Under load not enough fuel was grtting to the cylinder. That is what they said, I only know a little about it so I couldnt argue very much, but I'm not having them do the work. Bonehead, I will look a little closer for that, Thanks. The code said fuel leak making low fuel pressure so that could be something. I dont have any faith in the dealer mechanics, they just want to replace parts and not really find out what is happening, at Graff Chevrolet anyway


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## snapperlicious (Aug 11, 2009)

What kind of filter do you have? I mentioned this earlier in a post about my filter. I tried a metal filter from autozone and it ran fine until I put a load on it. Then threw a code saying low fuel pressure check filter. I found out my truck doesn't like those metal ones and have to use the plastic or carbon filter from ohreilly.


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## HOU Razorback (Feb 21, 2014)

The early model Duramax's (2001) in particular were known to have bad injectors. I think they actually carry a 100K warrenty on the injectors because they were found to be bad. 

If you still have stock injectors, I would get them replaced. I think your dealer may be right this time.


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## artys_only (Mar 29, 2005)

*Bad injectors*

the one that they had problems with where the first 3 years they made them . most people that had them the dealer replaced them and gave them 150,000 mile warranty. 2006 they installed the new design injectors in the LBZ motor.. and they still warranty them to 150,000 miles .


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## rglide09 (Mar 21, 2012)

My 2002 DMAX had the bad injectors, I replaced them at 132K miles after the crankcase filled with diesel fuel. Mine was too far out of warranty for any dealer help. When I replaced them I added a AirDog fuel filter/lift pump. The thought is the injectors will run lean towing heavy loads causing the injector body to crack. Today the truck has 183K miles and no injector issues. I tow a 13K LB 5th wheel with no power loss issues. The LB7 is a great engine, just needs a little help getting fuel to the injector pump. The AirDog maintains 10 LBS of fuel pressure to the injector pump.


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## bentman (Jul 23, 2007)

I had the same problem there is a 90 in the fuel line and when the motor gets hot it starves for fuel then the truck will go to reduce power there is a service bulletin out on it


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