89 4.0 running rich

My 89 MJ, 4.0 is running rich, and has a slight loss of power. Exhaust smells rich. I have done a few searches, but not much luck (& time) with them. Can I have the basics as to what to look for? Thank you in advance.

godchaser said:

My 89 MJ, 4.0 is running rich, and has a slight loss of power. Exhaust smells rich. I have done a few searches, but not much luck (& time) with them. Can I have the basics as to what to look for? Thank you in advance.

Click to expand...

Whats your mileage?
Whens the last time you changed the o2?
Whens the time you gave it a tune up?
Is your air filter clean?

Mileage 120,000.
Haven't done the O2 sensor. I always thought that when they go, motor runs horrible. I am in the process of a tune up, I'll write back with some results...

Sorry to hi-jack but im having the same problem and didn't want to waste another thread for the same topic.

Anyways Its a 92xj 4.0 aw4-242. Tires are 235x75x15's if that helps. Also it has 138,000miles, just replaced crankshaft position sensor, map sensor, coil, plugs, wires. Also recently replaced the fuel pump and fuel filter. Air filter appears to be clean and i just had it inspected about a year ago and it passed emissions so i figured the o2 sensor was ok. The exhausts leaves of a rich scent to it.

Just checked my mileage yesterday and got about 110 miles/ out of 12 gallons which is around 10 mpg. This is a substancial drop of mpg whenever i first got it. I was averaging around 16. I'll be glad to reply with any other information that may be useful to get my mpg's back up to where they were.

godchaser said:

Mileage 120,000.
Haven't done the O2 sensor. I always thought that when they go, motor runs horrible...

Click to expand...

Nope. When the O2 sensor goes (and that seems to be the case with you), the engine runs pig rich but otherwise runs well. The same also applies if either the coolant temp. sensor or the manifold air temp. sensor goes.
If the main load sensor (that's the MAP) goes, the engine becomes very difficult to start and runs like crap all the time. When the next load sensor (the TPS) goes, the engine starts OK but has an uneven idle and will cough and buck during changes in throttle position.
Other possible causes of rich condition are:

Plugged cat
Vacuum leak
Faulty injectors
Faulty fuel pressure regulator
Ignition problem causing misfire and leaving fuel unburnt

Thanks for the info. I guess I'll have to shell out the beans for that O2 sensor. I'll be sure to write back as I go.