I used to get really good fuel mileage. Around 18mpg with mostly city driving and 20+ on the highway. I just filled up and checked the mileage and it was 12mpg with all stop and go driving. (Northern Suburbs of Pittsburgh Pa). Any suggestions as to what happened. I know that winter fuel and ULSD takes some of the mileage away but I didn't think that much. I thought I might get better mileage with the #10 plate. I try to stay out of the pedal too. Any Suggestions? Thanks Pete

 

earlier in the winter, i was gettin the same thing, around 14 mpg.
Then the horrid cold forcced me to change the fuel filter and air filter.
Since the warmup, im back to about 22 on the highway.

Truck even pulls higher rpms now that the temp has come up above freezing.

 

Fuel leaks, boost leaks, air leaks, slipped timing, bad lift pump, and bad overflow valve could all be possible causes.

 

how about you filters?

 

I cleaned the pre filter in the fall. I changed the fuel filter about 6,000 miles ago. I replaced the return lines in September beacuse I had the fenders off and they were really easy to get to. I think the biggest change was the colder weather and the ULSD. Could it be the #10 plate. Does it need to be fine tuned? I have the plate in the stock position and I never touched the star wheel. Anything else I should try. Pete

 

Check fuel pressure, replace the OFV, and see if it makes a difference. The OFV is another huge contributor to bad mileage as well as a bad lift pump.

 

Where is the overflow valve and how much are they roughly? What about the lift pump?

 

Over flow valve is on the front of the injecton pump between the pump and the block. Cost is roughly 80 - 100 (probably not from Dodge). Lift pump costs between 90 and 150 (probably not from Dodge) (some have paid about 80 but seems those deals can be difficult to find. The lift pump is just in front of the starter and below the brake booster.

 

I'd be curious to know as well. Seems weird that you had a sudden drop in mpg as soon as you changed the fuel plate. I bet if you fine tune the position of the fuel plate, you could get better mpg. Don't know of anyone who's tried it though...

 

Anyone have instructions on how to fine tune my #10 Plate? Thanks Pete

 

Your plate and it's position shouldn't matter towards mileage as long as you keep the boost to a minimum. Before boost is built and while low amounts of boost are present the AFC "foot" is what limits the rack travel. I have an EXTREMELY deep cut #100 and rack travel mods but I still maintain 18.5MPG (uncorrected for tire size) in about 50/50 city/high speed driving as long as I keep boost to 10 PSI or less for the vast majority of driving. My .02

 

Thanks for the info. Pete