cylinder 4 misfire, P0204, p0304 only when hot.

My CEL intermittently comes on after restarting the engine at operating temperature. It will then run rough at idle and will bog down if I floor it. This will continue until I park it and let it cool down all the way. It seems fine after short trips around town, but starting and stopping on prolonged trips seems to trigger it.

It's a 2001 xj classic 4.0 with 150,xxx miles on it, it's also distributorless with a spark coil bar. The codes are p0204 fuel injector circuit condition, and p0304 cylinder 4 misfire. So far I've replaced spark plugs, TPS, and have tested the injectors with an ohms meter, which checked out fine. I'm going to go out now and swap injectors and do a compression test.

Any suggestions or ideas?

Compression test results

Cy.-Dry-Wet
1-155-179
2-152-179
3-160-179
4-170-187
5-165-184
6-167-185

Possible "Hot soak" or "Heat soak" issue.

Factory TSB NUMBER: 18-031-03, GROUP: Vehicle Performance, DATE: Sep. 05, 2003.

Yep this sounds like a textbook heat soak. I had it start last summer on my 2001. Just installed the ELK 960 timer for the electric fan. Virtually all accounts claim this to be the true fix, I will probably not be able to tell till next summer when the temps warm and the heat soak is the worst.

Good luck man I think you are $50ish in the timer and electrical connectors away from a fix!

P0204 is your clue.

You have an intermitant short or open in #2 injector trigger wire, a faulty #2 injector or faulty PCM. P0304 is a side result of P0204.

A heat soak condition as outlined in 18-031-03 does not cover P0204.

Look near the left rear of the head where the engine harness crosses over the rear left head bolt; the stud on the bolt likes to work it's way into the harness there and rub through wires. Seen that happen a half dozen times.

Well after swapping the number 4 and 5 injectors it ran fine for two weeks and then started running rough again today. Checked the codes and now its reading p0205, and p0305, so it must be the injector. I guess it would be a good time to do an injector upgrade.

Digger87xj said:

P0204 is your clue.

You have an intermitant short or open in #2 injector trigger wire, a faulty #2 injector or faulty PCM. P0304 is a side result of P0204.

A heat soak condition as outlined in 18-031-03 does not cover P0204.

Look near the left rear of the head where the engine harness crosses over the rear left head bolt; the stud on the bolt likes to work it's way into the harness there and rub through wires. Seen that happen a half dozen times.

Click to expand...

I totally missed my three typo's there... I meant #4 injector, and should have corrected intermitant (intermittent)

Good find too. Perfect way to proof your diag.

A few months ago, on my '98 XJ, the injector wire harness was rubbing against the end
of the fuel injector manifold and was intermittently shorting out the #2 injector. The
place where it had worn through was very tiny and I had not noticed it during visual
inspections. Only when I opened the harness sheath and checked the wires did I see
the exposed copper.