hey i have a 94 dodge 1500 318 with the nv3500 ive replaced the injectors replaced thermostat cleaned throttle body replaced all sensors related to throttle body the only thing left i can think of is the phlenum gasket but i dont have any vaccum in the crankcase which is supposedly the sign of bad phlenum gasket it does run rich i change the plugs guys i need some help i have NO idea what to try now the best mileage i got was 6 and that was 55 on the highway it also runs smooth and idles great besides the mpg this is a great truck please help

 

What size tires and gear ratio are you running?

Is the clutch in good shape?

Are your brakes dragging?

Is the exhaust free of restrictions?

Are the axle bearings free spinning?

Is the air filter clean?

 

Bad oxygen sensor? Bad coolant temp sensor?

 

i have a feeling your 4mpg has something to do with your calculating skills. how exactly are you calculating your MPG?

 

Agreed. Even setting your gas tank on fire, you'd be hard pressed to get that poor of mileage.

 

Yes clutch doesn't slip or anything its a perfect clutch

No we checked for dragging brakes all spin freely until the pedal is pressed

Yes it is a dual exhaust with thrush welded mufflers and it has the cat deleted

The axle bearings spin fine and the air cleaner was replaced as soon as i got the truck

 

No both were replaced didnt help

 

I get anywhere from 140-160 on a tank of gas it does have a 35 gallon tank and i checked to make sure the odometer was accurate and it is dead on i have the stock 355 gearing and slightly over sized tires not enough to effect anything also all of the injectors were replaced

 

If all you said is true, the plenum would be the next check. There's no "sure fire" test for the plenum. Some people have crankcase vacuum (I did) and some don't. Some see oil at the bottom of their plenum on the belly pan (I didn't) and some don't. Only real way to find out if it's blown is to pull it and look. If it's stock and has never been opened, chances are better than if a bear sh*ts in the woods that it's blown. With these engines, it's not an 'if' they blow, it's a 'when.'

If the mileage is still poor after doing the plenum, I'd suspect a gas leak somewhere.

 

are you 100% sure that you have a 35 gallon tank? have you e-mailed or gone into the dodge dealership and got a build sheet that says there is a 35gallon tank in it?