Did search, no results, maybe because it's a dumb question. Anyway, 2003, GMC 2500HD pulling a 30 ft 5er in the mountains. Have driven this route before with no prob. Yesterday (Mon 17th) different story. Going up some hills I was down to 30 MPH. First recommendation I received was, replace fuel filter. Sounds logical....except my MPG went UP when the truck was struggling. That doesn't compute in my feeble mind. Would the filter be your first concern?

Yes replace the fuel filter any time that you have lack of power.You can get one bad tank of fuel, and it might take 2 filters to correct the problem. It is best to learn how to change them yourself, if you can do that sort of thing yourself, and keep one in the truck at all times. Even if you can not change it, you might be camping in someplace like Yellowstone, where the nearest Napa store is 75 miles away, but someone can change it locally. If you did not have on in the truck, it would mean parking the trailer (to no damage the engine while it is starved for fuel and pulling a load) and go get one. . . Back in the 90's when I had my truck, it was more likely to get a batch of bad fuel, when steel underground tanks where more common. Back then, it was not ab-normal to change filters every 4 months, while some would last 2 years.As for the fuel mileage increasing, the less power that you are making, the better your mileage should be. Try driving it like there where a egg between your foot and the right pedal, and slow to 35 on the hills, you will see tremendous increases in fuel efficiency and MPG figures too!Good luck,Fred.

Yes, I'd check the filter first. If it's like an OEM Ford diesel filter, it could have a water proof membrane in it that stops a lot of junk. You didn't say anything about a water-in-fuel light coming on, but I'd still check the filters. It's cheap to check if it isn't the problem.Bill

I'll add a resounding "DITTO" to those suggesting the fuel filter. But I'd also check your air cleaner filter too! Seen too many stories lately of critters getting in there and making a home out of it.

Thanks all. Yes in Tow/Haul. One fuel/air filter change coming up.....

Duramax Struggling | Good Sam Community

25 Replies

Elbert
Explorer
Aug 24, 2015
get the fuel filter changed and carry the truck to the gm shop to see about the CEL and the fix... Or find a good transmission shop in your area...most of those are private home owned type places...but I'm guessing not many work on teh allison.
Perrysburg_Dodg
Explorer
Aug 21, 2015
No on AAMCO IMO. Ask around for a good transmission shop or take it to the dealership. Killerbee might have the ability to check it for you. PM him and see.

Don
N-Trouble
Explorer
Aug 20, 2015
Passin Thru wrote:
I changed to the CAT adapter and use CAT filters, $15 ea. Get about 1100 miles on a filter. Fuel mileage goes up, ( runs leaner) , and less power when filter is plugging. Change my own, cut a door in the wheel well and put screws in it so I can reach it easily. Fill it with fuel and replace it so I don't have to pump 1000 times. I am an Aviation Mechanic so I don't get dirt in it.

Your filling the filter with UNfiltered fuel... Not recommended. If your having to pump 1000 times you have a leak.
FlatBroke
Explorer II
Aug 20, 2015
Passin Thru wrote:
I changed to the CAT adapter and use CAT filters, $15 ea. Get about 1100 miles on a filter. Fuel mileage goes up, ( runs leaner) , and less power when filter is plugging. Change my own, cut a door in the wheel well and put screws in it so I can reach it easily. Fill it with fuel and replace it so I don't have to pump 1000 times. I am an Aviation Mechanic so I don't get dirt in it.

Is that 1100 miles a typo?
Passin_Thru
Explorer
Aug 20, 2015
I changed to the CAT adapter and use CAT filters, $15 ea. Get about 1100 miles on a filter. Fuel mileage goes up, ( runs leaner) , and less power when filter is plugging. Change my own, cut a door in the wheel well and put screws in it so I can reach it easily. Fill it with fuel and replace it so I don't have to pump 1000 times. I am an Aviation Mechanic so I don't get dirt in it.
mkirsch
Nomad II
Aug 20, 2015
guidry wrote:
In tow haul mode?

Tow/haul mode has NOTHING to do with the power output of the engine. It merely alters shift points and locks the torque converter in the transmission on lower gears for less slippage and heat buildup.
Hoppypoppy
Explorer
Aug 20, 2015
Thanks. Anyone trust Aamco? Also, could this be a contributor to the original issue? Sorry if these are dumb Q's. I am just an old dude trying to get by.....lol
_40Fan
Explorer
Aug 20, 2015
P0700 is just telling the ECM that there is a TCM code. Need a scanner that can access the TCM to get the proper code for diagnosis.
Hoppypoppy
Explorer
Aug 20, 2015
OK, back again. Although no cel showing I took the truck in to see if it threw a code. It threw P0700 which is a Transmission Control Module. Is it possible this could be part of my issue? Also, would anyone know a ballpark number for repair on this? Thanks again.
N-Trouble
Explorer
Aug 19, 2015
My best advice would be to pick up an Edge CTS monitor. You can monitor all kinds of parameters, see and codes that are set, and check injector balance rates, etc. Personally I wouldn't drive a diesel without one.

There are lots of these that guys have been selling used over on the Duramax forum as Edge recently released a second version. Nothing wrong with the original though.

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Duramax Struggling

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