P0303 Code and CEL

JLANEF

JLANEF

TJ Enthusiast
Joined
Jan 9, 2019
Messages
138
Location
Chandler Arizona
I usually post on my 1999 TJ project. But I am helping my son on his 2001 TJ. He has gotten a PO303 code now that trips the CEL. He has changed out, the fuel rail, spark plugs, added Cool packs, foil insulation kit around the fuel injectors and the OEM Insulator kit. He is still getting the code and feel some misfires. He lives in Minnesota and it was only 70 degrees today and it came on after a 15 mile trip with short stop, then a 30 mile trip with a 15 minute stop. Came out after the stop and started the Jeep. Good old P0303 was back along with the CEL light. Any thoughts? I thought this was a heat issue in hot climates, not in 70 degree weather?
 
Remove all the spark plugs and perform a compression test. Look for number three to be low. If the compression is good swap injectors, see if the problem follows.
 
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Daryl said:
Remove all the spark plugs and perform a compression test. Look for number three to be low. If the compression is good swap injectors, see if the problem follows.
Click to expand...
Swapping injectors is good advice. I think we do need to do a compression check!
 
JLANEF said:
Swapping injectors is good advice. I think we do need to do a compression check!
Click to expand...
Well my son had the coil packs off anyway so he decided to check the number 3 plug, (the only code we are getting, P0303), so he pulled it. it wasn't fouled and looked good, except for a definite brown spot on the white ceramic of the plug. Didn't look right. So he pulled number 2 and it looked good all over. Wasn't fouled and no brown spot. So we put the #2 plug in #3 and #3 in #2. To see what happened. By the way he has changed to high end Champion plugs a while back. He drove it for a good half hour, then stopped for 20 minutes, then drove back home and sure enough, CEL came on after about 10 minutes from when he was stopped. So got home and read the codes Misfire on 2 and 3 now, and the multi-cylinder misfire code. Anyone have any experience with the 4.0 not liking some plugs?? what is the exact OEM plug that Jeep recommends on a 2001 TJ 4.0??
 
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