ok I have a 99 dodge ram 1500 5.9 gas auto, I tuned it with hemifever tuning, glass pack. My question is I put a 3 inch lift in it than 285/75/16 tires and regeared it I usede to get 15 mpg out of her and had good power on the highway but after tires and re gearing and its bad. I put 4.10 in it and at 120km/h its around 2300 rpm. wich is good but I get like 8 to 10 mpg now. and towing a light load down the highway its sluggish to accelerate. is this normal for a lifted truck with bigger tires? or am I crazy ?

 

The 5.9 isn`t known for good gas mileage even in stock form. But now that your running bigger tires and gears, and your using a hemifever tune your making more power, but the trade off is lower gas mileage. and also consider the 3'' lift, it doesn`t help gas mileage at all.


As far as your truck being sluggish, it shouldn`t be. Are you running premium gas with your tune ?, if not, you should be. Check for vacuum leaks, when was the last time a complete tune up was done ?.

 

33in tires and 4.10s is pretty darn close to close to stock final drive ratio. So youre OK there.

sounds like it is tune up time

 

Yeah, that's close to stock ratio, with bigger, heavier tires. At 75 mph, it gets tough enough to push that brick thru the air.....

Slow down to 70. Watch the MPG go up.

 

Everything in that post makes sense to leading to bad gas mileage. But the sluggish, it should be the opposite! Make sure you have premium gas, and a tune up is likely necessary.

 

I'm in a similar situation (1996 1500 4x4/5.2/auto/hemifever program running the lowest setting with 87 octane gasoline/2" lift/4.10 gears/285-75-16" tires, roof height fiberglass topper) and getting around 10-11 mpg. I've also got a 50mm Fastman throttle body & factory air cleaner set-up, low restriction magnaflow muffler. Very recent rebuilt fuel injectors installed and Melling high-volume oil pump, and a recent new fuel pump. It's not a slug, but it's not a speed demon either. Aerodynamics of a brick - got it. Plenum replaced way-back-when.

So dumb question, but what do you all consider a "tune-up"? Would my mpg improve if I ran a higher octane gasoline and the next higher hemifever program setting? All the "parts" on the throttle body (the plug-in things) are factory originals (and I gave the throttle body a good cleaning when I had it off when replacing the fuel injectors).

I love my truck (just over 200,000 miles) but would love a few more mpg.

 

Plugs, wires, cap, rotor, air filter, pcv valve. (get the valve from the dealer)

How old is your front O2 sensor?

 

If the gas were you live has ethanol in it, it will rob power and performance. I can`t run the lower grade gas in my truck here were I live because of the ethanol, my truck runs like crap. I run nothing but premium all the time now and my truck runs good and has more power.

 

it hasn't been that long since a tune up 3000km maybe I do run regular fuel I will try premium I also did a hughes plenum not that long ago the truck of the line it a beast lots of torque but at highway the gas has to be more than 3/4 down to maintain speed

 

just yesterday I took the boat out (light speed boat) drove a round trip of 250kms used almost a full tank
oh and I do have a glass pack in it but its not really that loud maybe plugged cat?