My 94 4.0 I6 with AT started running strange a couple of weeks ago. The gas mileage went down, and when at temperature, when going about 45 at a steady speed, the engine feels like it is misfiring. This very similar situation happened a couple of years ago, and then the CEL came on with an O2 sensor. I replaced it and it fixed the problem. I was thinking this was the problem again, although with no CEL. I bought and replaced the O2 sensor, but it did not change the problem at all.

I checked the code with the ignition key trick and got 55 which should mean no codes. The plug wires have been replaced recently.

Any suggestions on what else might cause the problem?

thanks!

 

check to make sure your spark plugs and wires are on 100% and make sure they are not touching the block

also, i had something very similiar happen to me after i got gas in mine

turned out to be a bad tank of gas (i dont care what anybody says, different stations have better or worse quality of gas)

I ended up running that tank till about 1/4 full...put a new filter on and ran the next 2 tanks of fuel 93 octane. One came from a mobile, the other was a shell or bp......those 3 stations in my opinion have the best quality gas

stay away from lower mom and pop stations

now, im not saying that is your problem, but mine sounded the same, and that solved it...im sure others here will have there suggestions:thumb up:

 

Check all the wiring between the engine and firewall. Not likely a problem on a 1994, but on my 1997 cost me $100s of wasted codes and no nothing mechanics. Cheap to check.

 

I recently replaced both the wires and plugs. Just checked the wires and they look good.

 

Doing some searching I came across the possbility that it was the Engine Coolant Sensor. I ran this test on it:
http://www.justanswer.com/jeep/26cfm...-cylinder.html

And it was fine. Still stumped as to what is going on.

 

Finish your tuneup. Distributor cap, rotor and fuel filter.

Never underestimate the importance of these parts.

 

Have you checked your vac lines?

 

Mine was just doing something similar and it ended up being the Idle Air Control Valve. It wasn't closing and letting too much air through causing really high gas mileage and loping/stumbling. May be worth checking out.

 

Did the problem start shortly after replacing the wires? If so, try putting the old ones back on temporarily. The quality of some aftermarket wire sets leaves something to be desired.