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1999 Jeep Grand Cherokee WJ, 4.7, Quadra-Drive
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Discussion Starter · #1 ·
VERY occasionally I start the Jeep and have a rough running, flooding engine. Stinky catalytic converter and all. Warm, Cold, Driven 5 minutes ago, Parked all week, doesn't matter. Will not self clear no matter how far I drive. HOWEVER, if I simply turn it off, and remove the key (may not be necessary), and restart it, the problem is GONE until the next time it decides to do it. Never happens while driving, only on start up. Otherwise, runs great. Only codes are 442&455 evap. (1999 WJ 4.7L, Bought used ~6 mo ago, Stock except puck lift)
 

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VERY occasionally I start the Jeep and have a rough running, flooding engine. Stinky catalytic converter and all. Warm, Cold, Driven 5 minutes ago, Parked all week, doesn't matter. Will not self clear no matter how far I drive. HOWEVER, if I simply turn it off, and remove the key (may not be necessary), and restart it, the problem is GONE until the next time it decides to do it. Never happens while driving, only on start up. Otherwise, runs great. Only codes are 442&455 evap. (1999 WJ 4.7L, Bought used ~6 mo ago, Stock except puck lift)
Have you got the fault codes yet?
 

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What is status of the P0442 and P0455 - have you look into them ?
 

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1999 Jeep Grand Cherokee WJ, 4.7, Quadra-Drive
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Discussion Starter · #5 · (Edited)
Have you got the fault codes yet?
The only codes have been the 2 evap ones. I even tried driving it once to see if it would clear, and though it was surging, stalling, shaking, etc... it didn't throw any misfires or anything.
Is this happening on humid days? Older cars used to do this on humid days when the spark plug wires and distributor caps were bad.
That I will have to pay attention to in the future. I will look into the coils and plugs and see if I can discern anything.
 

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1999 Jeep Grand Cherokee WJ, 4.7, Quadra-Drive
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Discussion Starter · #6 ·
What is status of the P0442 and P0455 - have you look into them ?
Honestly I have not gotten anywhere with them yet. The very first time I noticed this problem I had a full tank of gas and the jeeps back end jacked up for a day. I figured I'd just ended up with fuel in the evap canister or something. Since then, I have tried unhooking the vacuum lines from the engine to the evap system while it was exhibiting these symptoms, and it made no difference at all. I assumed this meant it wasn't evap related. Could I be wrong here?
 

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I was thinking the purge could be stuck open causing a lean condition.
> over fueling can cause canister particles to gett to purge valve.
Maybe try crimping shut the purge to engine vac line for a test.
The EVAP will not run every drive so the issue will seam intermittent.
 

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1999 Jeep Grand Cherokee WJ, 4.7, Quadra-Drive
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Discussion Starter · #8 ·
I was thinking the purge could be stuck open causing a lean condition.


Maybe try crimping shut the purge to engine vac line for a test.
The EVAP will not run every drive so the issue will seam intermittent.
I did suspect that, so I have previously tested the purge valve and it is working properly. Also, I have removed the line and plugged it with my finger while it was misbehaving, and there was no change.
 
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