I have gotten as high as 21 right now averaging 18. '95 2wd, 318 5-speed

 

Well its an old thread. But I get in Canada 24 mpg @ 75 mph. thats 3 hrs hy way, and 1.5 hr city.
92 cc rear drive. 5.2 auto w 3:90 rear gear. 225-70/15 wheels. Cold air home build / 3" single exhaust with no cat, and Gibson headers./ Keg intake mod, / true double roller chain(mopar) / Mopar performance computer/ Harland sharp 1.7 roller rockers / port matched intake and headers / lowered 3-4/ aluminum one piece shaft/ box cover... Need body work, and paint yet.

 

My '93 3.9L 4x4 gets close to 12mpg. lol. Very little highway driving. Mostly small town main streets.

 

Heh. I've just added my Fuelly banner to my .SIG - but it's not quite the full story (it includes a 10MPG or so run while fighting the plugged cat, the bad TBI injector AND a failing ECU ...).

Currently I'm getting about 18MPG at speeds up to 75MPH on I-20 and I-49.

I've got it in my list to replace the front bumper (to get the black rubber piece under the bumper back on the truck!) and my next tires will be LRR (Low Rolling Resistance) units, since I drive so much highway.

Also, replacing the bent driver's fender and door, and replacing the weatherstripping around, should not HURT any *grins*

RwP

 

94 3.9L had 9mpg when I bought it. SO far I did the wires, plugs, cap, rotor, switch plate, coil, PCV, MAP,IAC, TPS Oil Sensor, EGR, O2 sensor, timing chain with added tensioner, and Hughes Engines intake plenum kit.
It got 16mpg+ or 365 miles on 22 gals all in town and the next tank got 17.27mpg or 380 miles on 22 gals with a 210 mile highway trip. This is with the cheap gas!
I figure doing all highway would get me 400+ miles per tank and I still need to solve a tranny issue. I feel lucky.

 

Just replaced my IAC that was bad, Hopefully that'll help a bit. Still bogs down when cold though >.<

 

You don't have to do the hughes engines kit the Chrysler TSB fix was to just replace the intake plenum gasket/s which leaves it to happen again. The problem is the sheet steel of the plenum expands/contracts at a different rate than the aluminum intake which over time destroys the gasket seal allowing oil into the intake. This affects everything. I figure the straight TSB repair would be good for a few years if that's how you want to go. You should still get new bolts to torque the intake down.
My intake was black inside I had to have it tanked it was so hard to remove. Then I just replaced all the sensors on it as 3 temp sensors are in a hard to get at place and the rest on the TB were also 20 years old.
Hughes Engines stepped up to create new plenum's out of aluminum to make the repair permanent. They make them for the 3.9, 5.2, 5.9 motors.

 

For OMGnanerpus.
Try changing out the single coolest temp sender. There is two left of the thermostat .
Smaller one helps control cold start up running also, and the before cat O2 every 40-50 thou really does help warm engine run, and milage.
Just my 2 cents.

 

Has anyone ran the Hughes injected air gap intake on the Magnum 5.2 ???
Iv heard of milage gains with them, but as well heard negative on lower milage, and low end torque loss ??? Any input helps.

 

Will definitely check that out! Thanks