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Need help..have a 2008 2500HD LMM and is garage kept. Not used for work and maintained diligently. Recently I discovered my fuel mileage dropped from 14-15 mpg to 10 mpg in city driving. Very little towing, but when I do, performs well. Truck has 103k miles. Couple months ago had injectors cleaned (all injectors within specs), new timing belt, new air filter, cleaned sensor, and change fuel filter when indicated. No codes. Engine runs smoothly with no apparent issues, good power production but the DIC shows loss of mileage. Anyone have any ideas?
 

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If the truck is stock this could be a restricted DPF in the exhaust. This will cause the system to go into regen at much quicker intervals and since diesel is used to burn off the carbon in the DPF this will kill your mileage. Dean
 

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If the truck is stock this could be a restricted DPF in the exhaust. This will cause the system to go into regen at much quicker intervals and since diesel is used to burn off the carbon in the DPF this will kill your mileage. Dean
Is there a test to check for DPF restriction?
 

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Is there a test to check for DPF restriction?
I know of test pipes that are installed to check the restriction. A shop with a quality scanner might be able to show you how frequent the regens are happening. There is a sensor in front and behind the DPF they might be able to see this real time. Don't have too much experience with this since I deleted most of that. Others with more experience might chime in here with more info on that but frequent regens will take your mileage down quite a bit. Here is a link that describes this and shows what to look for. Dean

 

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If you are in an area where you can get away with it I would delete the DPF and EGR function. I did that with a 70HP tuner and went from 15 to 16 MPG to 18 to 20 MPG. Also the regen is accomplished by injecting fuel during the exhaust stroke which will help wash oil off of the cylinders. Not good for long term life on the LMM. If I am not mistaken the LML used a 9th injector in the exhaust for the regen to do away with washing the oil film off of the cylinders and getting fuel in the oil. Dean
 

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Will the dealer be able to diagnose this problem?
That is a 50/50 proposition at best. If the dealer has a good diesel mechanic than yes, if you have a good diesel specialty shop in town I would talk to them first. Just my opinion. Dean
 

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I 100% agree with Dean. If you can get away with it delete it and enjoy better fuel mileage and a touch more power. You won’t regret it!
 
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