I'm getting between 17-21mpg in my truck (94, 12v, auto, 3.55's). I'm hoping that goes up once I rebuild the front brakes...

Not to hijack but I'll take any extra mileage I can get. Where could I get the timing bumped? I've got two local diesel shops, guessing they could do it?

 

i just went on a 2,500 mile trip and was getting on flat land 10 mpg and then in the mountains i was getting 7.8 mpg.

i have 2,600 to get back home again. i am looking at spending $1,700.00 in just fuel for this trip.

i am still fighting my fuel mileage problem too. i did the following and still don't have it fixed:

new injector tips
5" straight pipe exhaust
advanced timing
turned pump up
new air filter
new fuel filter
new over-flow valve
cut holes into bottom of stock air housing to allow more air before filter

 

RJ 66, what speeds are you running? Your mileage seems way too low.
I usually keep it around 65 when on a trip and get around 20mpg.

 

Hi. I'm new to diesel power so I went with the popular belief of bumping my timing to 16 degrees. The local diesel guru did his magic and lo and behold my milage went from 27 mpg(imperial) to approx 18 mpg. Don't know what happened but I will return to see him and find out why. I wonder if he cracked a line somewhere. I did detect a loss in low end power after the procedure.
I'll follow this string with interest.

 

anywere from 60-70 mph. the best i got was 12.77 and the worst was 7.87 mpg.

 

RJ ,that's much worse than I get. I'm not an expert but have you checked closely for fuel leaks? I had a leak in my return line last year and saw a drop in mileage before I saw the evidence under the truck. Check for any wet spots under truck , does it crank over several times before starting?
If not I'd try to find a good diesel mechanic and see if he can help.

 

Just ripped 20.76 MPG. 630 miles & 31 days between fill-ups. With old Diesel Dynamics Stage III that haze almost all the time.

 

I believe the timing does help. Personally i am at 16.5* and love it. As for the question about ignition or pump timing, they are the same thing seeing as there is no "ignition" source except from the fuel itself. With my limited knowledge of the exact workings of the P7100 pump I have come to conclude that people mess with the star wheel and by doing this they increase their low boost fueling which in turn adds fuel when you are cruising causings a net fuel loss. Correct me if im wrong, just my thoughts aloud. I am currently getting 17-18mpg highway with 40" tall tires, a 5spd, and 3.55's. Love it.

 

If my IP is leaking right at the line could that cause bad mileage?
I usually get 16.2
Not hard to start at all though. (usual 1/4 pedal starts.)

I also would like to know if the starwheel turned up DECREASES fuel mileage overall?

 

For what its worth, I drive a 98 auto, club cab long bed 4x4. When I first got the truck I couldn't really break 14, and around 12 city. Over the course of about 2 weeks I replaced front hub/wheel bearings, changed ALL fluids (trans. case, diff's, tranny, etc.) adjusted rear brakes and flushed system, and pumped STOCK SIZE tires (245/75-16) to max. of 80 PSI. By the end of all this I was getting 18-19 town and 23-26 highway. Now I'm up to 33x12.5's at 60 psi, but I haven't seen less than 16 in town and 20 highway. I also drive with a pretty light foot, usually no more than 8 psi boost.

 

I also believe that the starwheel affects smoke more than many people realize, more low boost fuel tends to increase smoke, which is just unburned fuel, so I don't see how it couldn't hurt MPG.

 

Any fuel that isn't going where it's supposed to go to push you down the road is going to decrease your mpgs.

 

I wanted to add my thoughts. I know you've got a 12-Valve and I've got a 24-Valve but some things that I've tried will apply, regardless of engine. When I first bought my truck, it had 204,000 miles on it so it already had a significant number of miles. However, with just a few changes/upgrades/repairs I have seen a steady increase from a low of 13.6 mpg to a high of 16.8 mpg of almost entirely in-town driving. Maybe twice a month I take it out on the highway for an extended drive but most of our roadtrips we take in my wife's car so my truck is mostly a commuter. The list, in order, which I've done in search of more mileage:
1. Rotated, balanced and filled tires to correct pressure.
2. Had oil changed.
3. Cleaned air filter (re-usable K&N).
4. Replaced 3" exhaust with 4" Stainless Steel turbo-back exhaust.
5. Replaced thermostat
6. Drained and replaced rear differential fluid.
7. Replaced fuel filter
8. Adjusted valves.
Also, when I bought it, I took it straight from the seller's to the shop where they repaired the transmission and performed a 4-wheel brake service so I don't think I should have brake-dragging issues.

My next step is Amsoil fully synthetic lubricants. My first changeover will obviously be my engine oil later this week. Next month, I'll follow up with Amsoil transmission gear oil and synthetic ATF for the T-case. Still later, I will replace the diff fluids again with synthetic diff fluids. I feel that an average of 15 mpg around town is acceptable and beats the heck out of my multi-port fuel injected overdrive-equipped Chevy 350 pickup which got a pretty consistend 10 mpg around town.

Personally, I think you should be doing much better. Hope what I've done may help you in your quest for better mileage.

 

I just took a 310 mile trip on Sunday. Average speed was 65 mph and got 22 mpg (converted to US gallons).