i have a 98 dodge ram 1500 4x4 with a 318and has 113,000 miles on it. in the last few months my fuel mileage droped and it lost alot of power i tried replacing the o2 sensors,plug,wires,cap,rotor,and air filter. the vacuum and fuel pressure are good too. a friend of mine told me to try replacing the map sensor but i dont want to buy one if it wont fix it. anyone know what it could be?

 

Check the plenum gasket.

Take your airbox off, unbolt your throttle body and look down inside your intake. If there's oil pooled up your gasket is blown. There's a few different repair kits for it, andton of information about it on this page. Just search "plenum gasket" if you want to know more about it.

 

One other thing to check is the Cat..you said you replaced the o2's did you test the cat? if clogged might cause the same problems.

 

I'm with jmhai. Check the Cat

Cheers Kayakman

 

I replaced the plenum pan gasket right after i bought the truck about a year ago. But i am going to check that and i also thought it could be the cat so i gutted it so now it sounds bad,has no power and uses alot of gas. i have a cherrybomb on it now but itried the stock muffler and that didnt help either. when i read the vac it was where it was suposed to be but if i have the heat on vent and jump on the gas it will go to defrost till i let off so i thought maybe a vac. leak and checked the hoses and sprayed starting fluid around the manifold but the rpms didnt jump