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99 XJ idle issues...possibly fuel pump???

IROCthe4.0

NAXJA Forum User
Location
connecticut
Ive got a 99 XJ 4.0L AW4 4x4 This started about 3 weeks ago. I changed the plugs and wires in my Jeep. I used champion plugs and a good brand of wires(forget the name). Anyway after I finished and drove it the motor developed a stumbling idle. It would idle fine but every now and then the revs would drop and the idle would get rough, would only happen for a second and only when stopped. Then the revs would go back to normal til it did it again. I figured I prolly needed a new cap, so I replaced that, didnt help. So now as of recently its been getting worse. The stumble lasts longer and is more frequent. It drives fine but has this stumble. When it happens it kinda shakes the whole Jeep. Theres no codes and no CEL on. Im thinking this could be a sign of the fuel pump going. What do you guys think?
 
I would look at "cause and effect". IF this stumble started IMMEDIATELY after you changed the plugs and wires, that may be the cause, particularly a bad wire or bad connection of a wire. However, if it happened a bit after the plugs/wires, yes it could be simply a coincidence and you now have to track down the new problem. Checking fuel pressure is easy. Get a fuel pressure gauge and place it on the schrader valve on the fuel rail. Get readings when engine is running (dynamic) and not running (static). Compare to factory spec. You also may want to consider cleaning your throttle body and as long as you're at it, remove and thoroughly clean the idle air control with throttle body cleaner. Good Luck!
 
I should mention that Ive gone over and checked and rechecked everything I did with the plugs/wires. All looks correct. Im gonna have to get a fuel pressure gauge.
 
I'm having the same issue on our '98, just checked fuel pressure numbers, all seem OK. Did you ever find the cause of your problem? I'd be very interested to hear what it is if you did. Thanks!
 
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