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rccolacc
12-24-2005, 10:15 PM
I have a '97 ZJ 5.2 (130K miles) and have been having some intermitent stalling problems. Also, you can tell the Jeep is running rich at idle. The check engine light is on and it's saying the O2 sensors bad, even after I replaced it. Because it's running rich, I thought it was a temp sensor gone bad. I checked on the coolant sensor and manifold temp sensor and they both were within resistance tolerance at given temps (according to the service manual). Then I decided to try the MAP sensor. I made sure the sensor is getting 5 volts with the key on. After warming the engine up, at idle the sensor shows 1.2 volts between wires A and B (the black and red wires). The book says it should be between 1.5 and 2 volts. I will try taking the sensor off and cleaning it in a few days. All the MAP sensor does is convert vacuum pressure to voltage right? Should I start looking for a vacuum leak or is the sensor really bad? Do you think this low MAP sensor voltage contributes to the intermittent stalling and the engine running rich?I'm getting around 15mpg on the highway at 70mph with stock everything (no lift or tires).
Thanks for your time.
-RC

rccolacc
12-24-2005, 11:46 PM
Ok I was doing some more thinking after posting this...
Does low voltage MAP sensor reading/vacuum have anything to do with the intake plenum gasket going bad? I've been about a quart low every time I change the oil (5K miles or so) the past 2 times. Burning oil would make the exhaust smell different and also affect the idle....
I'll take off the air bonnet from the throttle body and look down it to see if there's any oil deposits there within the next few days. Would that intake plenum gasket going bad affect vacuum?
Thanks.
-RC

zjoe
12-27-2005, 12:07 PM
The jeep is saying bad 02 sensorS? Did you change both of them? On a '97 you should have more than one. Maybe you didn't change the right one. Good luck!

rccolacc
12-28-2005, 01:43 AM
The jeep is saying bad 02 sensorS? Did you change both of them? On a '97 you should have more than one. Maybe you didn't change the right one. Good luck!
I changed the one that matters (the first one). From what I've read the second O2 sensor behind the cat doesn't throw check engine light codes. It only makes sure the first one does its job. Am I wrong?
-RC

CurtP
12-28-2005, 09:25 AM
There should be two upstream O2's - one for each bank of cylinders.