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2000, Jeep Cherokee Misfires

HI, I have a 2000, Jeep Cherokee 4.0L. The check engine light, keeps coming on, and the scan tool, shows P0300, P0301, P0302, P0303. Misfires in #1, 2 & 3 cylinder.

I replaced the Coil Pack & all spark plugs with genuine jeep parts from the dealer. Can you, suggest what might be wrong or other things to check? - Thanks Tom

One thing to do is a leak-down test on those cylinders. I had a 2000 Jeep come in with multiple misfires on adjacent cylinders and it turned out the head gasket was leaking between the cylinders.

Tester

I looked this up and this appears to be a distributor based system. Are these the original distributor cap, rotor, and wires? If so, you are way overdue for new parts. The rotor to distributor contact points fry with use, materail vaporizes, and the insulation on the wires dries up and can leak to ground. Your entire engine is ground.

Start with the basics. Try finishing up the tuneup that you’ve started and see if that works.

HI, it is a coil on plug system, it has no distributor or wires. I also would like to know if there is any other way to find a bad head gasket other then a leak down test? - Thanks _ Tom

A leak-down test is the most effective way to detect this type of head gasket leak. Because this is a static test. Which means a constant air pressure is applied to a cylinder to detect a leak. A compression test might not detect this type of leak because it’s too dynamic. The pistons move up and down so fast the compression isn’t able to escape thru the leak fast enough and you get a good compression reading.

Tester

HI, I been also losing little Antifreeze as well, I think it is a leaking head gasket. No one knew what was wrong with it, I will keep you updated. Thanks Tom

FYI, in 1999-2000 the 4 liter was changed from the traditional distributor to the coil on plug system, so the OP’s just after that change.

I agree that the leakdown test is the next step.

If all turns out well there I would move on to investigating the fuel supply. Do note that misfire codes/misfires are not specifically about spark. They are about combustion, so its air, fuel, compression and/or spark. Dealing with spark first is quite common. But checking for compression issues is certainly best to do before chasing one’s tail too much.