Engine/Transmission (1994 - 1998) Milage

[JoshPeters]

Ok guys. My truck has never gotten much for milage. Around 15 is average. That's city or Hwy. The BEST I have ever gotten was on a trip down little 2 lane roads running at around 55mph. VERY Rarely can I get lower than 14. I have a Valet switch, and have been driving pretty dang nice lately and I can't get much for milage. I do have Slightly oversized tires, but I dont' think that's going to bump me from 14. 8 on my last tank to 18+ as most of our members have. My timing is set at 16. 5 degrees... . I know it is for a fact... I just double checked it. I can't figure it out. Cruising along on a flat streach of road I'll be at around 65mph I've got, 8psi boost and 750-800Degrees on the ole EGT guage. Just so you all know... . this isn't a New problem..... it's been this way since I got the truck. Timing at 10degrees or 16. 5... . the only thing I notice is the powerband. No Milage change.



Josh

 

[GDollenger]

I think your numbers are very normal. I have had my truck for over 3 years and I have always gotten an average right at 15mpg. The best tank I ever got was 17. 4mpg but that was a flat all highway trip at 65-70mph. Everyday driving is always between 14. 5-15mpg though, and towing my 5ver I get 11. 5-12mpg.

 

[JoshPeters]

What's wierd is I can be running with people that have trucks in the like years etc and they are consistantly getting better milage. (IE going to and from TiM 2 years ago)



Josh

 

[TRCM]

but do they have the same rear gears ????

 

[bmoeller]

Hmmm. Good question, Josh. If I put my dually box back on, I was getting 17+ on the interstate after the engine mods. Couldn't break 16 stock. With the flatbed, 'bout the same as you. Your engine mods aren't that much different than mine, either.



Run any fuel additives? Lucas helps my mileage just slightly.



I wonder what would happen if you backed the timing to 15. 5 or 16* Haven't touched mine yet. Still stock, or there abouts.

 

[AMink]

If you have bigger tires and haven't corrected the speedo, you'll be going further than you show. Each revolution carries you further. Do you have the 4. 10's or 3. 5's in the rear end? Before I got sucked into TDR :-laf , I could get over 20 on the highway empty and cruising at about 60. Still up there if I drive nice. Around town is always about 15. I've been really *****footing around with the cost of fuel, and it does show in the mileage.

 

[JoshPeters]

I'm running 235-85R16 tires... . not to uncommon. I have 3. 54 gears. In about every other tank I run Power Service additive.



The other trucks have the same gearing as well. The only "notable" difference is they are not duallys.



I suppose I could drop the timing a degree. Thing is... when it had slipped to 10degrees... . I got the same milage as I'm getting now!



Josh

Edit, last night I filled with 31. 7gallons and went 458miles.

 

[TRCM]

Well, if you are running 235's, yer speedo is off by 5%, so your mileage calcs are also off.



and i get that mileage with 4. 10's in my truck. You got something wrong somewhere. Any fuel leaks ??

 

[bmoeller]

Figuring in the 5% (assuming it is correct), I still came up with 15. 17 mpg. With 3. 54's I'd think you'd be doing better as well.



I have 4. 10s in mine.

 

[JKouzez]

while we are on the subject of speedos i have 2wd 3. 55 rear end with 33x12. 50x16. 5 BFG mud terrains i know the speedo is off how would i go about correcting it.

 

[Lsfarm]

Try this

The fuel plate has a lot to do with your fuel mileage regardless of how gently you try to drive. You have the most fuel ineffecient plate and injectors in your truck according to your signature. Just look in the rearview mirror and you will probably see a haze or puffs of black smoke as you drive down the road, those puffs are now worth a penny or two each. The #0 fuel plate does basicaly nothing to control fueling, and the 370's aren't matched to our combustion chamber very well.



Try a #10 plate, or at the very least move your #0 back to the halfway point. Or reinstall your stock plate full forward. If you still have your stock injectors give them a try. Experimenting with the plate won't take that much time and effort, may be worth the effort.



The boost and EGT's you are seeing at 65mph are the same I see at 70-75mph, just how tall are those tires?? Do you still have the stock ones around and could try them for a tank or two??



Hope this helps. Greg L

 

[JoshPeters]

I'll definatly try sliding the plate back, after this weekend. :-laf I've got a pull. I've got a 6plate sitting here I could try that full back and see how that goes. I've been driving it so "easily" that I see very little soot. The only time I really see it is a puff on initial acceleration.



The tires are I believe overall height of a 33'' tire. I don't have the stock tires, and never really have, so that could play a role. That does make me wonder with the smaller tires wouldn't that bring me higher up in the RPM band at cruising speeds?



Josh

 

[CSnyder]

Gosh I feel really bad now since I got 20. 5 pulling a 32' gooseneck from Lacrosse, WI to Rapid City, SD going between 65-80 all the way on the interstate. Maybe it's time to get a 24 valve Josh??? I have gotten as good as 26. 7 just driving the truck around empty on longer trips. Chris

 

[JoshPeters]

Gosh Maybe it's time to get a 24 valve Josh???

Uhh I don't think so... . I have enough problems with everything else, I don't need a VP and LP to give me issues! I like my properly valved truck! :-laf



Josh

 

[hsmith]

Hmmmm. Really need to pamper that one. Must have been made on the Sabath.

 

[Cooker]

while we are on the subject of speedos i have 2wd 3. 55 rear end with 33x12. 50x16. 5 BFG mud terrains i know the speedo is off how would i go about correcting it.

You can get a different gear (the one that drives the speedometer) at the dealer.

 

[Cooker]

With a Valet Switch your AFC foot is never getting out of the way so I think moving your #0 will have very little effect on your MPG's.



You can however move the AFC housing which should have an impact on MPG's.



Going to a different plate, one with a profile , may help too.

 

[bmoeller]

I would slide the AFC housing first, before the plate. Will have a similar effect on fueling.



When I slid my plate full forward, I forgot to check the housing. Couldn't feel any more power at all. Checked housing, it was full back. Moved it back full forward, and



Haven't driven the truck much (been in the KW) since I did that, so can't really comment on mileage. No noticeable change at all, so far. Same goes for the 235 tires. To early to tell what change, if any, there will be.



235 tires aren't 33" tall. More like 31. 5- 32". Spec on mine is 31. 7". 255's are 33".

 

[JoshPeters]

So after the pull on friday, I'll slide the AFC all the way back as well as the plate to the mid position. I may try to crank the star wheel all the way... away from the engine... and see how it is.



My AFC's been off so many times... . I may have to heli-coil the holes pretty soon... the threads are gonna be worn out! :-laf



Josh

 

[Vaughn MacKenzie]

Cruising along on a flat streach of road I'll be at around 65mph I've got, 8psi boost and 750-800Degrees on the ole EGT guage.

That's hotter than mine runs cruising. At 65 I see 5-6lbs boost and a bit over 600. At 70-72 I see 8-9lbs boost and 675 EGT. Sub-stock injectors (180 Horse), #10 plate, 265-70-17" tires, 3. 54 gears w/5-speed, stock turbo, but DIY mildly ported head. If I don't get carried away 19mpg at 72-74mph is pretty easy. I've come in at 20 on 4-5 occasions running right at 70.



Vaughn