92 xj running issues
 

Hi all,
New to the forum
Reason for coming is a few tech questions about my jeep.
I have a 92 jeep Cherokee 4.0
"Problems"
-terrible fuel mileage 180kms to a FULL tank"
-when I am cruising at highway speeds it my rpms drop by 500-1000
Quickly and come back to normal. If I get off the gas or get on the gas it goes away.

"Things I have tried"
-New 02 sensor
-New fuel pump and filter
-Cleaned out the throttle body and sensors with proper cleaner
-check for vacumme leaks
-used injector cleaner for a few tanks of gas
-checked fuel pressure at the rail

My next guess would be a bad map sensor but what's your guys opinion I don't want to keep throwing parts at it.
thank you

For starters, miles (or kilometers) per tank means nothing. The only correct way to assess your fuel economy is by measured fuel (on the fuel pump) put in at fill-up, divided by measured distance traveled.

Distance per tank is meaningless.


As for your problem, a few questions:

1. How does your exhaust look? If it's running stupidly rich, you should have a lot of soot in your exhaust pipe, and you should see clouds of smoke when you accelerate.
2. How did you check for vacuum leaks?
3. Does your year Jeep have two 02 sensors? If so, which one did you replace?

Thanks for the reply, sorry The post wasn't detailed enough,
14.9 mpg
There are no clouds of smoke when I accelerate, the exhaust has a leak after the cat.
It has only One 02 sensor close to the down pipe.
Thanks for your time

Hmmm. 14.9 is not good, but it's not "your 02 is dead" or "massive vacuum leak" territory. I've seen that take it down in the 5-6 mpg range. That's pretty ugly.

Did you clean your IAC (Idle Air Control) while you were cleaning the TB?

Also, these beasts are pretty sensitive to grounding issues. It would not hurt to clean them up, and make sure your battery connections are good. I know, that sounds far-fetched, but it's really not. It's just good maintenance, anyway.

With that sudden change, though, and the response to the gas pedal, it's sounding to me more like fuel than electrical.

There is info around here somewhere on getting trouble codes out of the computer for earlier models that don't have OBDII. It's provably worth your time to look it up. There might be some clues there.

yes I did clean my iac when I cleaned my throttlebody I should have mentoined that!

the battery is new and the connections are good, I will clean up the grounds !

I have checked the obd1 codes by turning the ignition on and off 3 times ect and reading the engine light flashes, there are no codes other then the battery has been disconnected in the last 50 key turns. No onthee codes or engine light.