2002 4.0 misfires

[Speedwagon]

And just a heads up

Coil pack wiring is this
3 4
2 6
1 5
front

The 5 6 4 side gets me quite often, either at the coil or at the cylinders on that bank, 3.0l uses the same setup

These are Matched pairs, 1/5 spark at the same time, as do 2/6 and 3/4, so each pair shares one coil in the coil pack
[3 4]
[2 6]
[1 5]

That got me once. Ran horribly for a minute, until I realized what I had done.

 

[Speedwagon]

Update: discovered I had some less than perfect threads on 4 & 5. The plugs were not threading in all the way, so I ordered a reverse thread chaser to clean them up. Plugs go in all the way now, and everything is gapped to 0.062. So far, seems to be running well. Time to drive it and see how it does.

 

[RonD]

Good stuff

Time will tell

 

[Speedwagon]

It occurred to me, as I set out on a 2000 mile trip, that the other thing I had done when I changed the plugs, was clean the MAF. And I was still having issues on this trip.

Just swapped the MAF with a used one, and seems better on first drive. I knew it couldn't be the plugs anymore, because my last effort on that I was absolutely meticulous on gapping, properly seating, and wire routing. Every time I pulled the plugs, they looked lean. MAF explains that though. Idling much smoother now.

 

[Speedwagon]

I believe I finally have my answer! Long term fuel trims were consistently negative, and spark plugs kept showing lean. Looks like I have a bad O2 sensor.

 

[Speedwagon]

Well, I'm still getting idle misfires on this. Replacing the upstream oxygen sensors fixed the long term fuel trims, and brought them to around -5 now, instead of the -12 they were hovering around.

PCV valve replaced

Did a DIY smoke test, and couldn't find any vacuum leaks

Removed, cleaned, tested the ignition coil, and that all looks good.

What other possible options are there for idle misfires? Runs great once I open the throttle, but it's annoying at idle.

 

[Eddo Rogue]

Put all the old crap back on and start again one new part at a time.

 

[Speedwagon]

Put all the old crap back on and start again one new part at a time.

That's not possible. The spark plug wires came apart when I removed them, and so I tossed them. Along with the plugs that were in the truck when I got it.

It also doesn't make sense, because I've tried 2 sets of wires, and 2 sets of plugs since this started, with no change. So it can't be the plugs or wires.