First had error showing missfire in cyl 2 6 tech foud wiring harness puncture to yellow wire going to injectors repaired changed plugs , coil pack OK. Running beautifull now for 2 weeks . Yesterday error code p0420 popped up car still running fine . 420 seems to indicate catalytic converter problem. Wouldn't i be loosing power? Exhaust pipe blackened but may be due to original probs with cyl misfires. Can you advise me please. Thanks Much Fred
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Re: P0420 2003 Jeep Grand Cherokee 4.0 6cyl
This code is a catalyst efficiency code. The catalytic converter is most likely the problem, but it could still be caused by a defective oxygen sensor. The easiest way I know to check for this code is with a scan tool that is capable of reading live data stream. You need to look at the upstream and downstream oxygen sensors, and see if they are mirroring each other. In other words, if the upstream (the one before the catalytic converter) is reading .700, and the downstream ( the one behind the catalytic converter) is reading .700, or anywhere near that, then you have a problem. The numbers are just examples. The upstream should constantly swith from high to low voltage. If the downstream is identical, or even remotely close to having the same reading as the upstream, then you most likely have a defective catalytic converter. This does correspond to what happened a couple of weeks back. A misfire will take out a catalytic converter if not repaired quickly. Also, if you had a converter that was marginal, and was close to failure, then that misfire may have been just what it needed to fail.
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you mean the injector # 3 was dry ? Is that injector connector plug-in, wires ok ? do anything different ? Is harness ok ? Is plug wire ok ? you need to make sure you have power thru and to #3 , even new wires can be bad ! check for a short, continuity, and good ground. any codes stored in the ECM ?
Lets see coil pack, spark plug wire, spark plug, and if it is MFI maybe injector, or check injector pulse. If all those are ok, then check the compression in that cylinder, if it is low it will not fire right. Go through normal check out procedures to check each of these pull out the spark plugs, put them back on the end of the wire and check for spark. If these are ok the go on go the injector. If they are not try temporarly swapping spark plug wires with a different coil pack, if the problem follows the wire, then put on new wires. If it does not follow the wire, then the coil pack could be bad, or the signal going to it. If the spark is ok check to see if you have injector pulse signal going to injector. If it is ok replace injector. Hope this helps you.
Have you replaced the spark plugs?? Use good plugs such as ngk. Look for signs of carbon tracking on porcelain (black dirt looking marks that can NOT be wiped off. If present replace spark plug and coil boot to repair.
ok since you said you changed the plug and coil pack, start with the injector wire harness and look it over for any shorts or grounds, also make sure the terminals on the no.2 injector connector aren't loose. if you have access to a noid light you can check to make sure the injector is pulsing. check the no.2 plug wire as well. swap it with another wire if you can and see if the miss follows the plug wire. if those fail to solve your problem and the misfire remains on the no.2 cyl, try swapping an injector. if that also fails then you may have a problem with the cyl head.