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billyray80
billyray80, ASE Master Technician
Category: Jeep
Satisfied Customers: 3
Experience:  ASE Master Technician
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2003 Jeep Liberty Sport backfiring, not starting. Replaced

Customer Question

2003 Jeep Liberty Sport backfiring, not starting. Replaced spark plugs, coil pack (boots); appears 1 plug is not firing. No error readings when checking computer
Submitted: 6 months ago.
Category: Jeep
Expert:  billyray80 replied 6 months ago.
Hello. Since you've already replaced the plugs and coils, I would first check for spark. If you know which cylinder has a misfire, remove that coil and plug. With them removed, reconnect coil connector and put the plug in the boot, let the plug rest on something metal for a ground. Crank the engine and watch for spark. If no spark, there's likely a wiring or PCM problem. If there is spark, with that reinstalled, make sure the injector is working. If you have a test light, one of the 2 wires in the injector connector should pulse voltage on and off while cranking. The injector should click with the voltage also, but it is hard to hear without a stethoscope. If all of that is fine, check compression on that cylinder. If low or no compression, it has likely dropped a valve seat and will need a valve job. This is a common problem on these engines. I have also seen several break valve springs, which can be identified by removing the valve cover. I hope this helps and you get back on the road.
Customer: replied 6 months ago.
Thank you for your response. What is PCM?
Expert:  billyray80 replied 6 months ago.

The PCM is the computer that controls everything for the engine. It stands for powertrain control module. I'd say it's not very likely that it is bad though, they rarely fail.

Customer: replied 6 months ago.
Husband jiggled wires around, pulled some fuses, not sure why, but Jeep started. Strange noise heard while in gear, but it ran until this afternoon. Ran in the morning, but around 5 this evening, same scenario. No spark again.