The engine light came back on again after getting bogged down a bit in sand. I found 100 misfires on cylinder 1. The engine light went out on its own a day later. The symptoms have narrowed down to cylinder 1 only and when the engine idle drops. Both times the engine light came on when winching and driving offroad.

I already preformed a leakdown test however, I will do a compression test to be thorough. If it tests good like I believe it will I'll swap out the crankshaft sensor to see if that will help.

 

Dumb question, have you replaced your coil before? Ah nevermind I see you did. Mine had a dark terminal on 1 abd was causing me some grief. Let us know if the sensor clears it up. I would be curious to see the compression #.

 

One thing I took note of before the dealership replaced the left head, their leakdown test passed for cylinder 2, the compression test failed for cylinder 2. I'll post the compression results.

 

Update:
The engine has been running good without any misfires in daily driving conditions so I passed on the compression test at this time.
I still have to put the engine under a load again and check for misfires and/or voltage drop. The battery is new so if there is a higher then normal voltage drop under load the alternator would be suspect.
I feel there was a combination of problems, certainly I found a slight drag on the idler pulleys, the rocker bearings, and possibly an alternator not keeping up under load.
Side note on original rockers, they were not making any noise/tapping, Inspection found no play in the bearings. I finger rolled the bearings and they were smooth, until I tipped the rocker a bit and found a slight drag. It can be easily missed so I wanted to pass that along.

 

Update:

Did some light wheeling last Saturday and by Sunday the engine light is back on with p300, p301, and p305 codes. I checked the voltage while off road and found a steady 14v.
Today the engine light went out and is running fine.
I can now turn the engine light off (road driving for a couple days) or on (putting the tcase in 4wdr or winching).
Seems the engine light comes on when the rpms are around 700-800.
I plan to do a compression test tonight and a vacuum test at 700-800rpms.
I don't thing its a weak valve springs but the vac test will tell.
I also believe the compression test will be good as was my leakdown test however, I've seen other times when they differ.
Whatever the problem is I believe its isolated to the right head, maybe a cam phaser? or a solenoid that sticks?

 

Before the tests this morning the engine is running good, no codes with 2 misfires on cylinder 5
The compression test is good as expected #1-170, #3-165, #5-170
Vacuum is steady at 19" at 670-685 rpm, ran a test for exhaust blockage (cat) all is clear and working as it should.
I found the vacuum at 18" with the lights, fan-high, and brake lights on, idle stayed at 670-685 rpms, TPS 11.8
Same as above with AC/fan high on 16" 680-690 rpm, TPS 12.8
Battery voltage is 14v with lights, fan-high, and AC on or off.
Using winch at idle 12.7v idle didn't drop significantly
Before test I found 2 misfires on cylinder 5, after test I found 500 misfires on cylinder 5.
Took a short slow ride in 4wdr and found the misfires going down after restart, which means since the winch test there were no more misfires.
Took it for another ride (2 wheel dr) the engine is now idling rough with a pending multiple misfire. Misfires on cyl 3 (40) and cyl 5 (300s).
I suspect the more I drive on-road the misfires will go down.

 

Most of your numbers are less than concerning, I wonder if the ECM has a hiccup? Oddly enough I seem to remember seeing something about one of the casing bolts on the ECM was a grounding out, to fix the guy backed out the bolts that hold the ecm together ever so slightly for an issue is similar to yours.

I guess I should have read more but did you do a cylinder leak down test?

 

I'll do that, if it doesn't help I'll remove the ground strap and clean all contact surfaces.

 

I found a small amount of corrosion on the emc ground strap. After cleaning I found no change in misfires, still misfires when winching and 4wd use. The engine light temporarily came on once while normal road driving and went off on its own.

 

Did dealer replace all ground straps when replacing the head? Grounding is a big deal with these engines. There are many grounds under the hood and beneath the dash. Sounds suspiciously like grounding to me as it comes during high current draws such as using the winch. What about the braided ground between engine and body/battery.