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Unread 06-01-2006, 05:57 AM   #1
Scott98GC
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Join Date: May 2005
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Help Techs: Running Rich at Hot Startups

My '98 GC 4 liter is running rich and stumbling at hot startups. It's okay if its only been shut off for a couple of minutes, but for longer periods or unless it's fully cooled off it will buck and stumble until it cleans itself out. If I start it and rev it a couple of times, it will clean out and run fine.
I don't want to go to the dealer and have him throw parts at it until a cure is found. I'm thinking it may be a sensor telling the computer that the engine is cold and therefore telling the engine to run too rich.
Any ideas?

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Unread 06-01-2006, 07:13 AM   #2
greasefingers
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1994 ZJ 
 
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Location: Northern VA, USA, NJ
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You would need to know if she storing any codes. Even then it is no guarantee that a sensor has not drifted. How old is your oxygen s sensor? I hear 1998 model has trouble retrieving codes by the manual method? You could try this: Extracting Fault Codes OBDII (with digital odometer display)
Newer (OBDII) models - Put the key into the ignition, push down the odometer reset button, then turn the key to RUN with your finger on the button - and then release the button. The odometer will go through 1111111 through 999999, and then display the car's serial number. It will then show the error codes
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 06-01-2006, 07:37 AM   #3
Scott98GC
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Thanks for the reply.
Mine won't display codes using the above method... what's the other method?
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Unread 06-01-2006, 07:49 AM   #4
greasefingers
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1994 ZJ 
 
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Extracting Fault Codes:
Turn the ignition switch ON, OFF, ON, OFF, ON and observe the CHECK ENGINE LIGHT. The CHECK ENGINE LIGHT should begin to flash a series of codes. The flashes will be separated by short and long pauses. The long pauses separate the "ones" and "tens" positions, and each code from the next. A code 55 will be displayed at the end of the test.
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 06-01-2006, 07:52 AM   #5
greasefingers
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1994 ZJ 
 
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Location: Northern VA, USA, NJ
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You cycle the key to on/run and not start. Do it quickly.
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 06-01-2006, 09:11 AM   #6
Scott98GC
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I couldn't get it to go into code display mode. Mine must be one of those '98's that needs a code reader.
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Unread 06-01-2006, 09:14 AM   #7
greasefingers
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Yea that seems to have been reported here a few times. I do not know why that model year is such a PITA.
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 06-01-2006, 09:15 AM   #8
Scott98GC
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It's got 100,000 miles on it now. I've only had it a year, but according to the previous owner's service record, it's never had a new O2 sensor.
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Unread 06-01-2006, 09:17 AM   #9
greasefingers
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The v8 will also run rich if the ERG valve is stuck closed, as this dilutes the gas mixture in the cyl and lowers the combustion temp.

I would at the very least, pull a plug and examine the color.
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Cheers Steve

94 Black Laredo 4-Liter with QuadraTrac (42RE trans & NP249 TC) 200,000 + miles purchased new

88 Cherokee 2-door with 5speed manual 139K miles(deceased) purchased new
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Unread 06-01-2006, 08:23 PM   #10
Scott98GC
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Has anyone else had these symptoms?
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Unread 06-01-2006, 09:05 PM   #11
GreenDean
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Location: New Jersey, Exit 105
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Mine does this in the heat. I dont worry to much.. just the old engine blues.
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