Engine/Transmission (1994 - 1998) Fuel mileage blues

[JoshPeters]

Well first thing... . 295's aren't the factory tire. You can recalculate due to that, and I'd guess you'll gain a bit there. The overflow valve and timing can give you bad milage. The other thing I'd do is keep your foot out of it. My milage has gone up considerably due to that alone. Keep the boost UNDER 15psi while accelerating and see what happens.



Josh

 

[surfbeetle]

I have had my truck since new in 95. I had 4. 10s in it and always got around 18 mgp at 70 mph, rpms were close to 2000. My mileage around town has suffered since I put in the fuel plate because I have a lead foot. On the freeway, it is still the same as before the plate.



I just had 3. 54s put in it, that will help in the mpg. Also, I would not switch ratios only for the sake of attempting to get better mileage because you're looking at $1700 just for that. Unless you do alot of driving, you would definitely have a long time to break even. My rear end went out and I figured if I had to buy a new diff, I might as well bump it up.

 

[JHastings]

I have been kind wondering about my mileage too. Does my 160 pump hurt my mileage compared to your guys bigger pumps? I get 14-15 in town and 17-18 on the highway (Unloaded) and I drive conservatively. Also I have 265's and no leveling kit or anything. My truck does pour white smoke in the mornings, with large white clouds when I shift. Do you think my timing slipped and could this hurt my mileage a lot? Any guestimates of having my timing checked or whould I just go buy all the tools? Sorry for all the Q's.

Jamie

 

[JoshPeters]

Jamie... . No problem with all the questions... keep them comming!



I'd say your timing has Definatly slipped if you have white smoke like your takling. With studs and O-rings I'd go to probably 17degrees. The problem you may have is, take it to cummins... . they'll only set it to factory... . most shops won't bump the timing. If there is a diesel performance shop near you, I would suspect they would be able to do it for you.



Timing can DEFINATLY cause a lower milage number.



Josh

 

[DHorstman]

Truck:

1998 12V 180hp, Q-cab, 3. 54s, 173K, OE injectors, stock(&sloppy) 47RE



Mods: #6 plate, 3K GSK, 4" exhaust, amsoil air filter, large Ranch Hand front bumper, skyjacker D25 front coils and 285/75 R16s.



Cruise speed of 70-72mph, EGT ~680*, 12-14psi boost, empty & prettly flat ground.



Adjusting for 7% tire diameter, combined mileage dropped to 15. 5-16ish, with stock 245s was ~17mpg. Straight highway has seen a best of 20 mpg, with 285s & leveling kit.



Dan

 

[NHays]

Well. Gentlemen,

Oo. Thanks for all the response and help to my original post. I know I can always count on this forum/club to help in any way possible with any problem or question. It usually takes quite a bit to impress me but time and again this site has done just that. Again, Thanks for all the help and advice. I will keep yall posted on the truck.



Norman