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Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!ZJ (93-98), WJ (99-04), WK (05+)
All ZJ/WJ/WK specific tech questions asked here!
Since getting this WJ, I have changed the coils (NGK) and the plugs (champion platinum). It would barely run before that. I picked up a cheap code scanner to figure out that problem.
Now it will start and run smooth until it comes off high idle, then it will start to sputter and die.
If I keep the idle above 1000 rpms, it will continue running until I let off the gas. Once it gets below 500rpms, it will try and die again. If I give it some gas to keep it from dying, it will start missing and the check engine light will come on.
Checking the codes, it showed it had four coils misfiring. Shut it off, let it set for a minute, fired it back up, runs smooth until after high idle then Wash, rinse and repeat.
The previous owner replaced the IAC valve with an off name one along with a few other sensors along with the heads. They look like junk yard replacements not New.
I have cleaned the throttle body and replaced the IAC valve with two from Pull a Part. The battery is less than a year old and checks out good. The alternator is charging so it has the voltage it needs
sorry for the rant, I tried to cover everything I have done so far.
IIRC there are capacitors in the center of both heads that are wired into the ignition system. I would suggest that one or both of them are shorting out when they get hot. It's something to check out anyway.
IIRC there are capacitors in the center of both heads that are wired into the ignition system. I would suggest that one or both of them are shorting out when they get hot. It's something to check out anyway.
How do I go about checking those? I think I remember seeing those when I changed the coils and plugs
I'm not an electronics tech, but the old school way I would test them is to get them hot, disconnect the harness, short out the 2 terminals together, then check for continuity. There should not be any. Another way would be to use an analog meter (one with a needle) and see if they hold a charge. After being disconnected, test the 2 terminals for 12v. The needle should flick once as the charge is dissipated thru the meter.
OR you could swap them for junkyard units and see what happens. What they are designed to do is absorb the back-EMF created as each coil's magnetic field collapses to produce a high voltage spark.
I'm not an electronics tech, but the old school way I would test them is to get them hot, disconnect the harness, short out the 2 terminals together, then check for continuity. There should not be any. Another way would be to use an analog meter (one with a needle) and see if they hold a charge. After being disconnected, test the 2 terminals for 12v. The needle should flick once as the charge is dissipated thru the meter.
OR you could swap them for junkyard units and see what happens. What they are designed to do is absorb the back-EMF created as each coil's magnetic field collapses to produce a high voltage spark.
Got it! I have a digital multimeter my old analog one bit the dust years ago. Thanks!
Engine: 4.3L with headers and full 3" exhaust system
I think your O2 sensors are worn out. When you start it it will run rich until the sensors get hot then run off the data they give the ECM. Nobody ever changes them as a normal tune up part, but they need to be changed periodically
I think your O2 sensors are worn out. When you start it it will run rich until the sensors get hot then run off the data they give the ECM. Nobody ever changes them as a normal tune up part, but they need to be changed periodically
I have never heard of an O2 sensor causing a vehicle to shut off when hot. Normal failure mode is to just run stupidly rich.
Thats the thing, It doesnt get the chance to even get warm! At first start, it will run up to 1600rpm then come down to 1100rpm. Thirty seconds to a minute later it will come down to 450rpm for about fifteen to twenty seconds then just fall off to nothing and stall out.
Now this is after trying three different IAC valves and cleaning throttle body (which wasnt dirty enough to cause problems. It wasnt dirty at all).
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Have you looked for vacuum leaks? They are famous for causing variable idle, and changing with temperature is also a vacuum leak signature. if it's the intake manifold, anyway. Hoses, not usually.
Have you looked for vacuum leaks? They are famous for causing variable idle, and changing with temperature is also a vacuum leak signature. if it's the intake manifold, anyway. Hoses, not usually.
I think your O2 sensors are worn out. When you start it it will run rich until the sensors get hot then run off the data they give the ECM. Nobody ever changes them as a normal tune up part, but they need to be changed periodically
I just want to say the original 02 sensors in my 2000 4.0 WJ lasted until 230K miles before they, one by one, died. At one point they had lots of oil run thru them until I rebuilt the engine.
Engine: 4.3L with headers and full 3" exhaust system
Originally Posted by dave1123
I just want to say the original 02 sensors in my 2000 4.0 WJ lasted until 230K miles before they, one by one, died. At one point they had lots of oil run thru them until I rebuilt the engine.
I understand your position. However there are people on this forum and another XJ forum that had this exact problem that fixed it by changing the O2 sensors. Yes they can last a long time, but that doesn't mean they are working properly. They wear out just like solar panels because they generate electrons (current) to be measured by the ECM. The reason I suggested this is that the engine runs fine until it goes into closed loop, then starts to miss at idle. When you first start an engine, it runs on open loop from the O2 sensors until they can get hot enough to do their job. And as I stated, this is a tune up part everybody neglects.
06-25-2021, 08:53 PM
At my wits end with my 04 WJ Limited
