Engine/Transmission (1998.5 - 2002) Fuel Mileage Question

[DartVader]

Hi,



My 2000 4x4 automatic diesels mileage has been going downhill. It used to get 17. 5 around town, and 20 on the highway. About 9 months ago it started going down (14-15 mpg), and I started getting the dead pedal. I figured it was because of the VP44 failing. Well I changed the VP44 before Thanksgiving, the reman VP44 that I put on had something wrong with it. The truck smoked bad at start up, it was hard to start, the mileage went down to 13. 5 mpg, and it was throwing a code. I called the company and they sent me out a new one under warranty. I put the warranty VP44 on the truck, and I also replaced the cam sensor and have been running it for about 2 months. Everything is fine, starts easy, no smoke, but the mileage is still going down. I am getting 13 mpg in town, and on a recent trip with the cruise control set I averaged 16 mpg. Does anyone have a suggestion on what could be the problem? Could it be the VP44 again? What else causes a diesel to drop mpg like that?



Thanks in advance.

Reid.

 

[DFerverda]

Check and clean your map sensor. Also the Iat (intake air temp sensor). They can both cause bad mileage. I just put new ones on my truck, got em here.
Cummins Sensors

Check the manual for spec's and clean them before you spend $ to replace them. Sometimes if the map is bad, you will be down on power also. Also the ulsd with the winter mix may affect your mileage.
Which rebuilder did you use for the vp?
Good luck
Dirk

 

[DartVader]

I cleaned IAT sensor when I did the VP44. I will check the map sensor. I bought the VP44 through Pensacola Diesel.



Thanks, Reid.

 

[NDaniels]

Check at the freightliner dealer also for map sensors- mine was cheaper from the one here locally.

 

[Pat@BD]

How many miles are on the truck? If they are over 150,000 and your injectors are the origionals it could be them starting to get a little tired. Now the Ultra Low Sulphur diesel can have a pretty big affect on mileage as well, but that switch over was done before last summer.

 

[Huff N Puff]

Make sure:

Hi,



My 2000 4x4 automatic diesels mileage has been going downhill. It used to get 17. 5 around town, and 20 on the highway. About 9 months ago it started going down (14-15 mpg), and I started getting the dead pedal. I figured it was because of the VP44 failing. Well I changed the VP44 before Thanksgiving, the reman VP44 that I put on had something wrong with it. The truck smoked bad at start up, it was hard to start, the mileage went down to 13. 5 mpg, and it was throwing a code. I called the company and they sent me out a new one under warranty. I put the warranty VP44 on the truck, and I also replaced the cam sensor and have been running it for about 2 months. Everything is fine, starts easy, no smoke, but the mileage is still going down. I am getting 13 mpg in town, and on a recent trip with the cruise control set I averaged 16 mpg. Does anyone have a suggestion on what could be the problem? Could it be the VP44 again? What else causes a diesel to drop mpg like that?



Thanks in advance.

Reid.

Your brake calipers aren't dragging the brakes.

 

[DartVader]

The truck has 187,000 miles on it. I didn't think the would affect mileage. Is there a way I can test them? No none of the brakes are dragging. I already checked that. Thanks for all of the suggestions.



Reid.

 

[Pat@BD]

Any fuel injection shop should be able to do a "pop" test on them. This is where the pressurize them and make sure they don't open until the correct pressure. If the pressure they open at is too low then you don't get a good atomization out of it and that could really affect performance.