I have a '94 Cherokee sport 4.0L 2wd. Recently my mpg went from about 16-17 down to 10-12. I just used some 44k fuel systems cleaner thinking that was it but its the same and seemingly getting worse... I don't know much about cars, especially troubleshooting. Any ideas? Thank you for any help or suggestions you can give.

Hi,

Bunch of stuff here ...everything from your driving habits to a clogged air filter. You admit you don't know much about cars; do you do any preventive/regular maintenance? ...Or do you essentially drive the thing until something bad goes wrong with it? Is the check engine light on?

If you've essentially done nothing to your ride (okay maybe get the oil changed) then there are many things that could cause a drop in gas mileage.

Start with the simple:

Tires: when was the last time you checked the air pressure in them? Stock tires on your ride should be run at 35 psi, measured when the tires are cold ...there should be a placard on the end of the drivers door with the factory recommended pressures.

Air Cleaner: If you've never replaced it, do so. Swap this out yearly

A little more involved; you can do this yourself with a good shop manual (Chilton's) or take it to a reputable shop:

Spark plugs: replace with factory stock Champions ...don't buy the high zoot cosmic plugs for $6 a peice (replace plugs every 10K)
Spark plug wires: replace with good aftermarket set (NAPA or CarQuest make very nice wire sets comparable to the factory wires).
Distributor cap & rotor: replace (Again, NAPA or CarQuest sell good stuff)

Get these done at that reputable shop you chose:

Upper intake cleaning to include scubbing the throttle body (the carburettor-looking thing the air cleaner rubber accordian boot is attached to) and a professional fuel injector cleaning (not the "pour-it-in-the gas-tank" liquid miracles you can buy at the store). You may have a stuck open fuel injector which would contribute to bad MPG.

Replace all the oxygen (O2) sensors. Depending on your setup, you may have one or two of these sensors. They are located in the exhaust tract, usually one is before the catalytic converter close to the engine and one is after ...they screw into the exhaust tubing and have wires coming out of them. These sensors are direct inputs to the fuel injection system computer and determine the fuel and air mixture. If they have gone bad then the computer is getting bogus inputs which will affect gas mileage. Normal life span on O2 sensors is 75-100K miles.

Do these things and check your gas mileage.

If things are still not up to par, you may have a clogged exhaust system. The catalytic converter may be plugged and/or the muffler may be rotting from the inside causing an exhaust flow restriction. Also check the exhuast pipes looking for any possible pinched or kinked sections.

Depending on how much you're willing to tackle will determine what this will all cost. I would say you're looking at about $300 to $400 bucks for everything except dealing with the converter and exhaust ...add another $250 or so for exhuast/cat replacement.

Hope this helps...

Mike
00XJ

Spark plugs: replace with factory stock Champions ...don't buy the high zoot cosmic plugs for $6 a peice (replace plugs every 10K)

I agree with everything above, except the 10k replacement for plugs. I've always done mine at 30k, and they've been good to go. 10k seems a bit early, but it would make sure they're always close to new.

One thing not mentioned is to check the O2 sensors (or have them checked). When they fail they fail rich, putting more gas into the system and reducing mileage. If the inside of your tailpipe is wet with gas, that's a sure sign of a bad O2 sensor.