P0301 - Cylinder 1 misfire on 2000 XJ after new head install

My brother & I just installed a new head on my 2000 XJ after the 0331 head cracked. We used all new gaskets, etc, including new injector seals & new spark plugs. After it warms up, now, it starts to run a little rough & then throws a CEL. I checked it with an OBD2 monitor, and it's P0301 - cylinder 1 misfire. I tried swapping the 1 & 2 plugs (plugs look fine) and the misfire still occurred in the same cylinder. I tried swapping the injectors for 1 & 2, and still the misfire stays @ cylinder 1. So do I start changing out sensors, like the crankshaft position sensor or the camshaft position sensor, or could it be the coil pack (it's the single-piece unit with 3 coils)? I have the FSM, and I've started following the test procedures for the injectors, but I'm not sure about testing the coil pack. Any suggestions? Does anyone in Sac/Yuba City have a compatible coil pack I can swap in to test if this is the source of the problem?

Do a compression test.

I would change the coil pack, or find a good one to do a test swap.

gradon said:

Do a compression test.

Click to expand...

X2^^ it doesn't take much error in tightening down a rocker arm to induce a misfire, and a piston ring/ cylinder wall that's worn out can reduce compression to the point of misfire as well.

Gotcha - thanks. I'll try the compression test first, since we have a gauge. I'll have to probably post up on the local board to see if someone has a coilpack loose or one on their Jeep I can borrow briefly to check if that's the issue if compression isn't the issue.

Did the compression test - good, even compression across all cylinders. Leak down test shows a good seal in #1, so at least I can eliminate that as a potential can of worms.

Now I have injectors on order from Precision Auto Injectors, but since the misfire didn't move when I swapped injectors from one cylinder to the other, I'm also going to track down a replacement coilpack (maybe from the local JY) to see if that eliminates the problem if the injectors don't.

Is there a possibility that the connector to the #1 injector is the sole point of failure? What's the best way to test for this?

Again, the problem only presents itself once the engine has warmed up.

It is possible to have a bad connector.
I think there is a tool called a noid light that you can check the injector pulse at the connector.
Correct me if I am wrong.
You could also swap the coil packs if I am not mistaken.

Yes, a Noid light tests the signal from the ECU at the connector, but you need to wiggle the noid light to see if the female connector contact is loose!!!!

Did you accidentally switch the #1 and #2 injector harnesses?