P0303 Cylinder 3 misfire

1998, 4.0L, AW4

I've got a very noticeable misfire on cylinder 3 at idle. It seems to clear up once I'm on the gas.

Fuel pressure tested at 49 psi.
I swapped a spare ignition coil - no improvement.
I changed all plugs, wires, cap, and rotor - no improvement.
Swapped injectors from cylinders 2&3 - it still misfires on cylinder 3.

I plan to Seafoam it thru the intake when I get a chance. Anything else I'm missing?

Howdy!



Have you done a compression check yet? How did the old plugs look coming out?

If you swapped injectors and it's still at #3. Swap the injector plug to verify the misfire moves with the plug. Then it's either the plug or the ECU.

Hopefully it's not what I encountered........
https://naxja.org/forum/showthread.php?t=1145993

stethoscope to check if that injector is actually firing?

compression test?

Update: I ran some Seafoam thru the intake and noticed that the exhaust manifold was leaking. Turns out it had tons of cracks in it that were all dumping right around cylinder 3. I think that the heat was vapor locking the #3 injector.

I replaced the exhaust manifold today and put on some new 4-hole injectors. She seems to be running fine now. Fingers crossed that the exhaust was the issue.