i have a 98.5 and it's only getting 10 to 12 miles to the gallon. truck has dr. perf. stg3 chip and 100 horse sticks but i figured it would get better than this. truck does not run very good it should run better considering what it has right? is it the injector pump please write need help.

 

Have the codes pulled on it first. Check your fuel pressure, change your air and fuel filter, check for boost leaks, clean your IAT and MAP sensors. What gears are in the rear end? Auto or stick? What size tires? Fill out your signature with your truck info so we can help ya better.

 

one ton dually stand. 3.55 gears with 305/12.5/16s. runs about 2100 rpm at 70. thanks fr the reply. where is the IAT located

 

Just a quick check since I had this problem - my manifold was cracked BADLY. Just replaced it, but my mileage was in your range (haven't done a full tank since replacement). Crawl underneath truck and look at manifold as well as looking from the top...just an option.

 

2100rpm at 70? Sounds a little high for 3.55's and a standard. My truck used to turn 1900-2000rpms at 70mph with an auto and 3.55's. I'd say that right there is part of your problem. The efficiency range of these engines is about 1800-2000rpms. Try driving about 65mph and see how that does. Also, have you had your speedo corrected for the larger tires? You need to add in 10% to your odometer when you calculate fuel mileage. If your speedo hasn't been corrected then when it's saying your running 70mph your actually running 77mph. Big difference in speed right there.

 

I finally got around to actually seeing how far my speedo was off since I put my 38's on and...........WOW I'm WAY OFF!! Drove next to my brother the other night, speedo said I was doing 50 and I was really going 65-66 mph..........

My mileage went to crap, needs to be re-geared!!


~Nick

 

I'm running the Dr P stuff and had something similar happen. When I added the 110hp sticks my mileage dropped drastically. I added the FASS and the mileage jumped right back up to 20+? Since your runnin the Dr P stage III box that means you tapped the Vp. I agree with Blue. Get it scanned for codes. D o you have gauges, fuel pressure?

Tye

 

im already running 2100 at 70 if i go any lower i'll be redlining. adding 10 percent only gets me 12.5 last tank. it might be because its so week its using all of the fuel or its just running out the tailpipe. i wouldn't mind the the crap mileage if it ran better. need a comp

tye how do you like your stg IVs

 

I'm confused by that statement. What do you mean if you go any lower you'll be redlining it?

 

Has your speedometer been corrected for your large tires? Like explained above, if your speedometer has not been corrected, you are actually running more than 70 mph(depending on the ratio of diameters of the tires you have now and the stock tire).... even with that, your mileage seems exceptionally low...

 

i ment if i changed to lower gears it would be pushing it at just 70. and i always add in the speed diff.

 

on my 2000 ctd we put 37's on and did not recalibrate the odometer or the speedo, my milage went to 10-12, after recalibrated it was at 18, so some how my math was way out, and to this day I cannot figure it out.
When you say you are accounting for the correction yourself, when you are running 70mph what does your speedo say? Just really high rpm's to only be at 70
just my thought on it

 

driving with a heavy foot in the city? 12 mpg? that sounds about right...first thing to try is driving like u have an egg under your foot and try anticipating red /green lights to avoid too many stop and go's....i always find people are surprised what a difference driving habits make

 

I was talking about slowing down 65mph, not lower gears.

The IAT sensor is located behind the MAP sensor. Both are located on the driver side of the engine behind the fuel filter canister.