So i just got back froma trip to Utah.... and i got crap mileage... we drove about 70-80mph almost the whole way, even up hill.... but i got crap mileage... i know i was doing 70-80mph but still i was turning about 2100-2500rpms and the best i got was 13.5 towing.... so on the way back i slowed to 65-70mph and the drive was all flat and down hill..... and i only got 12.8mpgs!!! i dont get it... last year i did the same drive with a heavier load.... like 5.5 or 6k and i got 15mpg consistantly.... and got 18mpg one part of teh trip... i had 3.07 gears then, but i was smoking everywhere i went.... turned the fuel down this year too, i pulled the laser cut dvs and ran the fuel plate in the pump in the stock position..... so why is my mileage so crappy??? thanks


jason

 

Cause you've got a p-pump

ok kidding aside

since you've got a 2nd gen 12valve injection system you'd probably get more knowledgeable answers in the 12v drivetrain forum.

But might replace the overflow valve in that p-pump

 

You say you had 3.07 gear "then". WHat do you have now? If you went lower than a 3.54, you are in the ballpark. I got 14-15 towing a donor rig (combined truck/ trailer in the 12K range) from OK to IN a few years ago with a set of 4.10s.

 

What's your timing set to?

 

What are delivery valves??

Whats a fuel plate??

I think the biggest diff. is in the gearing 2100 rpm's is out of the sweet spot for mileage.. around 1800-1900 is... the 3.07's you should of kept... what do you have now, 4.10 ?

 

Well i have 4.10s now... which are nice.. but i guess that means my mileage is gonna suck.........as far as timing goes i have i t set at 18* which should be good for the rpms i was turning... maybe i need to go higher... im gonna play with it a bit and see if i make any changes in the mileage. I was told 1800-2200 rpms on the cummins is their sweet spots.... im thinking not, cause last year i was turning 1900 rpms on part of the drive and i was hazing the whole way and still got almost 19mpg towing a heavier load..... oh well i guess ill have to keep my towing rpms down to 1800-1900rpms.... which is a safer spped anyways..... i checked my rpm to speed.... and i was actually doing 90mph more than i thoght... and i still got 13.5 towing... not to bad i guess... but definantly not safe. thanks guys

jason

 

Just some food for thought. I used to drive an '02 reg cab 4x4 3500 auto 24 valve, with 4.10's to pull an EBY 24 foot 102 wide stock trailer. (heavy beast) Empty hauling before an Edge EZ (65/150) the best mileage it ever got with me driving 60 MPH and pulling the hills conservativly was 11 MPG, loaded was 9. After the EZ it still only got 13.5 at best.

So yeah, the 4.10's are killing your mileage. I know they are some beasts for leaving a stop light, but I dont think they belong in a diesel. If you haul heavy on a regular basis, either Gear vendors, or 3.73's. Otherwise go back to a 3.54.

Oh, yeah I am an x big truck, owner operator.

 

Thanks man... i guess ill just have to keep my rpms in the 1700-2000rpm range and go slow... i guess i just went off of a few fellas who had 4.10s and a 5speed and they were getting 20mpg towing or not... they were also stock trucks........ maybe someday ill swap for 3.73s or maybe 3.55, but i dont tow very often so ill be okay, besides my next set of tires will be 38s hopefully thatll help. thanks again


jason

 

Heh, ya know what, I didnt even see you were running 35's! I think thats almost an equivilent to a 3.73 rear end ratio. Well, keep er under 2200 cruising if u want more mileage. 1800 is about the sweet spot.

 

I brought home a load of firewood in the trailer a couple of weeks ago(one and a half cord in a 2800# trailer). I got 15mpg with my p-pumped first gen. Bigger twins empty don't affect my mileage, but the bigger twins with the trailer dropped it about 1.5mpg.

 

Ya.... i was kinda hoping for better mileage with the 4.10s since my 3.07s just made me haze everywhere cause my turbo is to big to spool at low rpms... but even though im running clean... no haze and even under full throttle its clean... my egts still get to hot and my mileage sucks.... whats the deal? besides the rpm thing cause before this tranny i had a 727 with 3.07s and i ran basically the same rpms and sometimes higher, but i still pulled off better mpgs..... infact i got 21mpgs.... going up the mountains and back... i wasnt towing but still......

jason

 

Im gonna call timing. I heard that p-pump timing can slip. Dont know if its true, but that would explain high egts and low mpg's.

 

Yup it can slip on these pumps... unfortunantly, but i doubt thats my issue(ive done the timing like 20 times and never had it slip)..... ill find out after i get back from Pennsylvania.. i got a family reunion there so i get back on the 7th... im gonna check my timing and then advance it to 21* from 18*...... i think my turbo is too laggy......... all i know is my egts are to high for pulling such a dinky load...... and running empty (no trailer)at 75mph into the wind i was pushing 1200*.... and only got 15mpgs


jason

 

i wonder if your egt's are like that cuz of the 65mm turbine?? it sounds like you have alot of fuel..

and i still think you need to keep it around 1800rpm.

thats the sweet spot for a Ve truck,, not sure about an overfueler

 

Well i do have more fuel than the turbo can handle.... but this trip i removed the laser cuts and put the fuel plate in so i would get less fuel..... like i said before, the smoke clears fast and no haze... but egts go up..... i wont deny i was running the rpms a little high for mileage.... but.... ive gotten 21mpgs empty before and i was running 3.07 gears with a 727 tranny... so my rpms were still 2000rpms and up......it seems like my turbo dont like to spool... even with the 13cm turbine housing and 65wheel... it doesnt spool any quicker than the 14cm housing and 71mm wheel... which made more boost and alot quicker....... im still a little sore about HTT telling me this is a better setup....

jason