Mileage gone to hell

[jimnance]

I have a 1999 Dodge 2500 RAM with the Cummins 24 valve engine unmodified. 3. 54 Auto Quad Cab 4X4. 50,000 miles



I was getting 19 MPG overall mostly highway driving. Have not used truck for any heavy towing until about one month ago. I pulled a 9,000 lb fifth wheel about 150 miles. Since then I have lost 3 MPG and only average 16 MPG.



I have changed Trans fluid, fuel filter, air filter, engine oil, etc. and nothing helps. Transmission does NOT seem to be slipping. All RPM's and other operating parameters seem normal.



I'm thinking maybe I have a clogged injector, but the truck runs smooth.



Anyone have any ideas?

 

[jjdiesel]

auto transmission

My bet would be the auto transmission. Something has gone awry with the lock-up on the transmission. You can't really feel it... . but somehow its robbing your mileage. Had the exact same deal with my '95 and the transmission was the culprit. Sorry I can't be more specific but call the transmission guru's and they'll know.

 

[WyoJim]

Try tightening all the hose clamps from the turbo to the air intake. This fixed mine.

 

[Fast 1]

Maybe it's a batch of bad fuel, or just some blended fuel. Their is a big difference in fuels sometimes. Wind can also play a big part.

 

[boonsur]

I also think it could be the winter blend fuel. The anti-gel package reduces performance. You could try an additive with cetane boost, and see if that helps.

 

[Steve Campbell]

Air filter, fuel filter, lift pump IAT sensor dirty, but probably just the "winter fuel".

 

[Pit Bull]

My truck averaged 16, started using anti gel Rotella DFA and it now averages 15. I think it is the anti gel/fuel that is getting your mileage.

 

[Mschevey]

Have you checked for any codes in the ECM? If somthing set a fault code the MPG can get thrown off.



Otherwise I agree with the previous posts.



Mike

 

[YA_TO_UPA]

I also had a sudden drop in mileage, went from 18/19 mpg to 15/16 without a warning. Changed the lift pump the other month and I'm back up at the 18/19 mark again.