Engine/Transmission (1998.5 - 2002) fuel mileage is off

[AFoulk]

Ever since I bought my truck, my trip computer has always read around 1mpg more than what I come up with when I calculate my mileage by hand. Ever since I replaced my injection pump with a SO (it was a HO from factory), the computer has actually been . 5-1mpg less than I am getting. Filled up tonight, the computer said 15. 2mpg average, and I came up with 16. 3 by hand. I questioned this cause I know the computers in the dodges are usually overlly optimistic, and the SO pump has really killed my bottom end power... . I expected this, but not as bad as it is. Should I have reset my APPS when I replaced the pump? Some one told me you should, but I've never heard of that. Also, about 2 weeks after doing the pump, I had a code for the roadspeed sensor. I cleared it and it hasn't come back since. Could either of these problems have caused my mileage to be out of wack? I'm mainly worried about this as I don't want my odometer to be off.

 

[Wiredawg]

I can't answer your question, but I'm surprised the SO and HO trucks used different injection pumps. The SO engines put out 235 HP/460 Tq and the HOs put out 245 HP and 505 Tq.



Wide did you choose to replace HO w/ SO pump?



Wiredawg

 

[AFoulk]

because eventually my goal is to hit around 550hp, and the HO pumps start to run out of fuel around 500hp, the SO pumps will actually flow more fuel. Don't quote me on the sizes, but I think the HO pump has 7mm plungers in it, and the SO has 7. 5mm plungers. The HO's have slightly smaller injectors than the SO's, but are set up to fuel harder in the bottom end (this why the SO killed my bottom end) and the HO engines actually have 1 pt. higher compression pistons. All of that, plus I think higher fuel pressure (not sure on that) is where the HO's make their extra power stock. But when you start running bigger injectors and stacking modules, it'll start to run out of fuel in the top end.

 

[johncameron]

because eventually my goal is to hit around 550hp, and the HO pumps start to run out of fuel around 500hp, the SO pumps will actually flow more fuel. Don't quote me on the sizes, but I think the HO pump has 7mm plungers in it, and the SO has 7. 5mm plungers. The HO's have slightly smaller injectors than the SO's, but are set up to fuel harder in the bottom end (this why the SO killed my bottom end) and the HO engines actually have 1 pt. higher compression pistons. All of that, plus I think higher fuel pressure (not sure on that) is where the HO's make their extra power stock. But when you start running bigger injectors and stacking modules, it'll start to run out of fuel in the top end.

You are pretty much bang on with this.



As for your overhead, it will be off more expecally if you have changed some part of your fueling sustem or added a mod. They are never bang on even from the factory. It should be used as a guide

 

[Wiredawg]

That makes sense. I had an 2000 2500 with SO motor and 6spd. I traded for a 2002 3500 to better tow my 17K 5er. Never had EGT problems w/ the 2000, but I can't take my eyes off the EGT gauge on my 2002. My 2000 had more USABLE power towing.

I had the TST PM3 adjustable on my 00 and is on my 02 now. I could tow with the power level set on 6 on level ground and 4 on the grades. On the 02 its maybe 4 level on level and 0 level on the grades. And I lost 3mpg in the trade, have higher EGTs, but I still have more power. on the dyno

If/when the VP44 dies again on my 02, I might have to give a thought to an SO VP44 replacement.


Take care, Wiredawg