Q: 2002 Jeep Liberty Limited 3.7 misfire bent spark plug tip with rough idle

asked by on September 13, 2016

I have a 2002 Jeep liberty limited 3.7 L that appears to have misfired while I was just idling at a red light causing it to rough idle and bend the tip of the #2 cylinder spark plug as if something smashed into it. I'm not sure if some sort of corrosion material blew up through the intake and is now either stuck in the chamber or on the top of the piston itself that smashed into the plug or perhaps a bent valve? The OBD code I got was P0302 so I replaced the #2 fuel injector and installed new plugs with little if any changes. I'm ready to install a new coil pack along with the remaining 5 injectors but before I did I figured I better do a little research first. I noticed that this has been an ongoing problem with the 3.7 L v6 for some time now so I was also wondering if there was ever any kind of recall issued for this problem or am I looking at thousands in repair costs to fix it? Thanks in advance for your help.

My car has 152000 miles.
My car has an automatic transmission.

I can’t find any information suggesting there is a recall for your vehicle. Either way, you need to figure out what has failed in cylinder number two. Replacing all the injectors is not going to fix the problem in cylinder number two, so I would hold off on that. From what you have stated, I don’t see any reason to replace any of your injectors or a coil pack.

You should begin by doing a compression test. I suspect it will be very low in cylinder number two or zero. If you do indeed discover low compression, you will then need to determine what has failed inside that cylinder. It could be a valve or the piston. This is best done by performing what is known as a leak down test which involves putting compressed air into cylinder number two. You will need to have the piston at top dead cylinder, then you will listen in the tail pipe, in the intake manifold with the throttle plate open and in the crank case by removing the oil filler cap. You are listening for the hissing sound of air passing into one of these systems. Which ever one you can hear hissing is the area in the cylinder that has failed. The intake is the intake valve, the exhaust is the exhaust valve and the crank case is the piston or piston rings.

With a spark plug electrode damage and the fact that it still misfire after replacing the spark plug, it is very certain you will have a failure in one of these areas of the cylinder.

I recommend the following inspection if you decide you need help. Engine is misfiring inspection.

Good luck!

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