mntn-biker

My son's 2000 XJ 4.0L gets an occasional PO30X-Cylinder X Misfire (can't remember the exact cylinder but I have seen it do maybe cyl. 1 one time and then cyl. 3 another time). The XJ has about 157k miles on it. It has the ignition coil rail. It seems to run fine, he just complains that the check engine light is on again and we read the code and then clear it (I've got him trained to read and clear the codes on his own now ).

I haven't pulled things apart yet to check the plugs but I'm wondering if this might be a sign of needing new plugs or I have 1 of the coils going bad (maybe the coil rail needs replacing?). We bought this with 140k miles so I'm thinking the coil rail is original.

Mike

tjwalker

"Heat soak" is a common problem with the 00-01 that can set misfire codes. Are there any symptoms that go along this like possibly a bit of the engine stumbling upon a hot restart?

mntn-biker

Nope. It seems to start fine cold, warm, or hot. Just turn the key and she fires right up.

cranesrule

Fresh plugs first and we'll go from there... Note the condition of each plug as you pull them and post up.

tjwalker

I agree with fresh plugs. I like NGK copper plugs for the 00-01 distributorless ignition. Be sure gap is at .035 before installing them.

Another thing to verify with the P0300 code is fuel pressure. For a 2000, you should have 49 psi, plus or minus 5 psi.