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Unread 09-14-2009, 01:29 PM   #1
impuresoul2k3
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1993 ZJ 
 
Join Date: Mar 2007
Location: Nebraska
Posts: 565
Jeep is running rich and misfiring, sometimes.

Most of the time, my Jeep runs fine, albeit gas mileage is a little low (~13). On longer drives though(20mins+), it will out of the blue just start missing (can't cruise 60 mph, it misfires too much) and/or running extremely rich. I know it isn't that accurate, but the overhead console will estimate the mileage as dropping to 7-8mpg instead of the 20 or so it should be getting.

Turning the engine off and restarting doesn't help. You have to shut it off and let it cool down. Occasionally, possibly rarely, it will correct itself and start running normally again, but that doesn't last long.

Within the past year or two I have replaced:
  • TPS
  • Oxygen Sensor (a few months ago I believe)
  • Coolant Temp Senor
  • Plenum Gasket
  • Plugs
  • Wires
  • FPR
  • Oil Pressure Sensor
  • Battery
  • Radiator
  • Coolant Hoses
  • Heater Hoses
  • Air filter has been cleaned


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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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Unread 09-14-2009, 01:41 PM   #2
ezflip
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Probably O2 sensors, maybe a bad cat. Not sure how many O2's the 5.2 has (you hinted towards only replacing one) It could be you got a bad one, or did you go mopar? If not, change them to mopar sensors.
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Unread 09-14-2009, 02:01 PM   #3
rugermack
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My 95 5.2, has one O2 sensor.
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Unread 09-14-2009, 02:08 PM   #4
JackieChilesEsq
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I have a '96 and I have the same problem. The thing would barely go when I cranked it this morning. The longer I drove it, the better it ran, but still doesn't run great.

I took it by Auto Zone and they came up with the following codes:

1. 1. Throttle Position Sensor/Pedal Position Sensor circuit high input, code PO123

2. 02 Sensor Circuit High Volts Bank 1 Sensor 2, code PO138.

What will it take it terms of cost, roughly, to get these issues fixed?
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Unread 09-14-2009, 02:29 PM   #5
impuresoul2k3
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I forgot to mention, sometimes in the mornings, when its a cooler morning, the engine will idle real low (~200rpms) and quite rough unless I hold the idle up around 1500 for a few of seconds. Without intervention, it will sometimes stall. It also seems like if I push down the gas pedal to move forward in a line or stopped traffic or something, it will misfire a little bit if its 1200 rpms or under.

The 93-95 Jeeps have only one O2 sensor, mine probably has around 2500 miles
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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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Unread 09-14-2009, 02:41 PM   #6
impuresoul2k3
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And last bit of info, I don't have any codes
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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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Unread 09-14-2009, 02:46 PM   #7
WiCkeDuDe
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What brand O2 sensor did you put in?
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Unread 09-14-2009, 02:52 PM   #8
impuresoul2k3
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NGK. If it was the O2 sensor, wouldn't it manifest itself well before a 20-30 minute drive?
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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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Unread 09-14-2009, 03:18 PM   #9
ezflip
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Quote:
Originally Posted by impuresoul2k3 View Post
NGK. If it was the O2 sensor, wouldn't it manifest itself well before a 20-30 minute drive?
Not necessarily. Only after a bit of a drive is your jeep up to normal operating temps. Temps affect greatly if you run lean or rich. O2 sensor is probably wear I would start.
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2002 Overland - 4.7 HO, "Select-Drive", 4" RC long arms, TAG front winch bumper, 32" BFG KM's, Kolak 3" exhaust, Flowmaster 50 series


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Unread 09-14-2009, 03:43 PM   #10
StellaTheZJ
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The Crankshaft Position Sensor tends to go bad on a lot of our Jeeps. Many people have reported strange and intermittent missing can be cured by installing a MOPAR CPS. You've covered most bases, but left the coil, CPS, and Cam Position Sensor (inside the distributor). How about one of them?

Also, have you checked the ASD Relay for corrosion? Corrosion causes increased resistance with heat, and again, many have reported problems with the ASD relay.

Good luck!
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Unread 09-14-2009, 04:08 PM   #11
impuresoul2k3
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Good call Stella, I think I'll check those out before the O2. I mean the Jeep is up to operating temp plenty of time before it starts misfiring.
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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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Unread 09-15-2009, 10:23 PM   #12
impuresoul2k3
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Ezflip, I stand corrected haha. I had a friend hook up his scan tool and it turns out the O2 sensor starts reading lean, ~.1V and the fuel trims max out at +33%. Looks like its going back for a refund...

Its still kind of weird that it takes a longer-ish drive to get it to start running crappily
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1993 Grand Cherokee Limited, 5.2L
Modified/Slightly Ported Kegger
Air hat spacer
Modified Throttle body
Flowmaster muffler
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