hey guys,

I was getting 10mpg and the past two tanks have been 8mpg. I was wondering what you guys could think it could be. i havent done any thing different. I even filled up with 87 last time.

 

Just do a tune up. Plugs, wires, dist. cap and rotor. Air filter and other filters. Change all oils. A vacuum leak or bad EGR or O2 could cause bad gas mileage. Any codes?

 

What kind of engine do you have and how hard do you drive? I average 16.35 with my 3.9 Magnum. 10 sounds incredibly low. I'd start with a tune-up but if that doesn't solve the issue I would immediately replace the oxygen sensor.

 

I'm curious why you said "I even filled up with 87 last time."

If you don't have a performance computer in that truck, you shouldn't ever use anything but 87!! Octane rating is not a measure of how flammable the gas is or how hot it will burn, its a measure of the gasses ability to RESIST detonation! That is necessary on a performance engine so the engine can compress the gas more without it pre-igniting. The performance gains come from the higher compression and later spark, not from the gas. If you were running 89, or 91, 92, or 93 (whatever premium is in your area), you are causing your engine to not be able to properly ignite the gas and its causing colder combustion and not burning all of the gas so you now probably have a rediculous amount of carbon build up in your cylinder heads.

Your bad gas milage is probably a side effect of the carbon build up thats been happening in your engine. If it gets bad and starts to burn out, you probably have killed your o2 sensor as well.

Here is my advice... run seafoam through the engine to clean it (suck it straight into the manifold through a vacuum line), then once its clean, put a new o2 sensor in it and then do an ignition tune up and stop running high octane gas!!!!!!!!!!! Its important to replace the o2 sensor after running seafoam through it because the smokescreen that the seafoam causes will mess up the o2 sensor.

FWIW, my '95 5.2 5 speed averages 14.5 with me driving the **** out of the truck and 15.5 if I take it easy. I run 93 octane with the mopar performance computer, but its a requirement of the computer.

 

ha! i get like 5 MPG.... literally... fill it up and its like 210KM to a tank.... she loves the fuel...

 

i have the 5.2, i dont run it that hard or i try not to. the 87 is our lowest grade premium i usually run 85. i will do the seafoam and if that doesnt do it then i will change the out the ignition. someone told me today that they change the gas blend durring the winter vs the summer. have you guys herd of this

 

I have never heard of 85 octane! You should never run anything lower than 87! It says so in the owners manual and FSM! Sorry dude, I thought when you said that you were running premium gas like some people do. Forget everything I said about running high octane gas. It still wouldn't hurt to clean the engine with seafoam and put in a new o2 sensor though.

 

ok and you said to run it trough the manifold vacuum line and not through the gas. and it shouldnt matter if i run it through new oil should it.

 

Yes, when I used it, I pulled the brake booster line off and sucked it in through that line. Then you are supposed to turn the engine off for a few minutes and then run it until it stops smoking.

I would not run it through new oil. If you want to run it through the oil, do it in the last 50-100 miles of an oil cycle. Reason being, that stuff contains kerosene that can eat gaskets if its left in the engine for a long period of time.

 

ok i will do that when i have time. i will replace the dist. and pcv, the plaugs and wires arnt that old. it wouldn't be a bad injector