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I just bought a 2000 Land Rover Range Rover 4.6 HSE a few months ago. The Service Engine light was on. I scanned it and it came up "PO302" (cyl #2 misfire) I replaced the plugs and the wires and cleared the code, a mile down the road the light came back on and it has the same ("PO302") code. Thinking maybe the coil pack??? Any suggestions???
Hope that is the problem. The ECU tests crankshaft speed fluctuation to detect misfires to comply with the Federal Test Procedure for emissions. When they occur, at a level of 1.875% in 1000 revolutions of the engine, the system waits for it to occur again on the next drive cycle. If it happens again, light comes on. If the misfires occur at a higher rate, say 8.6% at idle, and 2.0 - 10.7% at 2000 rpm, in 200 revolutions of the engine, the light come on at once (cat damage possible).
So when you drove and got up to speed, the threshold for misfire tripping the system is reduced, and the light comes on at once, while it may have been fine at idle. Or you waited between testing at idle, turned off truck, then went on a drive and hit drive cycle nuber 2, light came on.
All that said, cheap/bad wires and plugs are more often the culprits.
Trouble code "PO302"
