recently bought an 04 hemi, I know the mileage is never going to be great but with the mods Ive done I think something is amiss. It has a camper shell, I switched from 20in rims to 17in, K&N CAI, SC programmer, magnaflow muffler with 3in tail pipe, MSD plug wires and royal purple oil.

On a recent 1300 mile trip the best I could do was 16.5 with cruise set at 65 this seems low to me. Am I missing something? Also I have tried the economy,87 and 93 tunes on the programmer and didnt notice a change with any of them.

Any help is appreciated.

 

Can't really help with the hemi.... Good to see another homebrewer though! Prost.

 

Take the camper shell off. It hurts MPG and replace it with a normal tonneau cover. Try changing the actual spark plugs themselves too

 

2003 quad cab hemi with camper shell (3.92 rear end / automatic)
Right at 100,000 mile (never in the shop) I get 12-14 around town, 17-20 highway and 11.5 when towing travel trailer. I use fully synthetic oil and it acounts for a 15% improvement when towing.

 

what size tires you running? What rear end gear ratio? Did you turn off MDS with the tuner? Several things can make or break gas mileage. I had 04 1500 5.7 285/70/17 tires. 4.56 gears. 16 hwy 12-14 in town. 8 towing. ( 8,000 lbs). I also ran sythetic oils in everything.

 

LOL....youre complaining about 16.4 on an 04? Mine NEVER has seen 16.....more like 9-10

 

Your mileage seems in the right range and maintaining 65 is a good comprise. I can get about 18-19 at 50mph and drops to 15 at 75. The tires can make a difference depending whether they are a highway, all season or AT/Mudder. I found the air presure can make a big effect. I normally run 40 psi front and 27 rear on my P series 20s. Actually picked up 1 mpg. I do not know where you are located, but here in the northeast, my mileage drops about 1 1/2 in town and 1 on the highway. It's a combination of running rich during warm up and the winter blend gasoline.

 

My bone stock 05 2500 2wd has gotten a best of 16.5 on the road. I tried the Volo Performance FS3 "add on" chip without success. It actually made my average mpg drop 0.5 and reduced my low speed throttle response.

You comment about SC 87 and 93 tunes not making any difference causes me enough concern to stop my plans to make a purchase. I'm hoping other readers can provide real world experiences with other tuners so we can all see which ones are making mpg improvements and which ones are not.

 

dumb question you have a 1500 or a 2500