I have had this car for about 7 years with only one major repair (transmission) and have seen poorer mileage every year. I am averaging about 11.6 miles to the gallon. I had the Oxygen sensor changed at the dealer about a year and a half ago hoping this would help, but it didnt help. The car runs ok except I think it should accelerate quicker. Someone had mentioned to me that the possible culprit could be a faulty MAP sensor or a plugged cat converter. The car is stock other than a k and N FIPk, a Fastman throttle body, and a powertrax locker on the rear. Any suggestions would be greatly appreciated. The vehicle is a 2000 with the 4.7 L engine 4x4 and 3.55 gears. Thanks in advance.

 

When was the last time you had it tuned up? Changed out the spark plugs? What tranny oil did they use? Changed out the air filter or cleaned it?

 

Recently changed plugs less than a month ago and also cleaned and re-oiled the air filter on same day. The tranny oil they used was the ATF 3. The mileage did not improve at all. When I first purchased the car, I was averaging 15 to 16 mpg. It was just a gradual decrease in mileage. That's why I'm wondering if something may be failing. No CEL has come on recently. It came on once (long ago) and that was a power steering pressure switch which was changed and that cleared it up. The throttle body has been cleaned as well recently. Thanks.

 

They used the wrong transmission fluid in your vehicle for one thing. Your vehicle takes ATF+4 and not ATF3. ATF+4 is a fully synthetic transmission fluid where ATF3 is not. All RFE transmissions use Mopar ATF +4 which is the transmission model designation for your vehicle.

 

what kind of spark plugs are you using? if you have anything other than cheapo copper core champions, then your doing it wrong, make sure they are champion copper core plugs and gapped to .040

yes you have the wrong fluid in the transmission you need ATF +4 so they put the wrong fluid in, i would get that fixed ASAP

what tire pressure are you running, does it pull to either side going down the highway, are the tires wearing evenly?

id suggest 35-38 psi

and what tires are you running, an aggressive tread pattern will eat gas too

 

I looked for my receipt from the transmission repair and it was noted as ATF 4 fluid. I am running 32 X 11.5 BFG All terrain tires and they are inflated to 40 psi. The pulgs I had before were the Bosch platinum ones, but I changed them to the original Champion copper ones that had been recommended by everyone. There was no change either. Thanks for the replies and ideas. Additional ones greatly appreciated.

 

Check for components that may be causing a drag on your D. Brakes? Have them check and make sure they are not grabbing the drums/rotors.

Did you replace both O2 sensors? One in front, one in back of cat. Usually when you change one, it is best to change both to make sure it is feeding correct information back to the pcm. Map sensor replacement may restore some power loss and fuel mileage.

Depending on mileage of your D, have you had your fuel injectors cleaned?

Throttle body/IAC cleaned also?

If you think your CAT is clogged, better go check it out so you won't lose an engine because of that.

 

ATF+4 is NOT Fully Synthetic see here (I did some research....LOL): https://dodgeforum.com/forum/1st-gen...f-4-facts.html


If the transmission is designed for ATF+3 then ATF+4 can and should be used. The 2000's and up have the new standard ATF+4 requirements. That said you can not use ATF+3 in a newer ATF+4 required lubrication transmission (2000 and up).



As for your question on fuel mileage:

You have 4 - 02 sensors on that rig. 2 pre-CAT and 2 Post-CAT (eg... 1 on each side before and after each CAT). Try to pull them out 1 by 1 and burn the tip of them with a torch to get the carbon off them (will look like red/orange particles) then reinstall.

As for the CAT's, you can take it to a muffler shop and have them perform a back pressure test on the CAT's. This will tell you if you have segnificant back pressure causing the issue. Most shops will do this free of charge. Anything over about 3 lbs from front to outlet I would replace.

Next thing I would do is check the MAP sensor and Air Charge Sensor.

 

Yes you are right about the ATF+4. The only excuse I can bring u on how I got that wrong is that Indy hit me with that voodoo doll.

 

2000s have the choice of +3 or +4. Original factory fill was +3. IMHO, when the service window comes up, swap to +4 and never look back.

45AutoPete,
sux to be u. LOL

IndyD