01 4.0 bank 1 missfires

[TJS1011]

My 01 4X4 ranger 4.0l is misfiring on 1,2, and 3 (bank1). I've changed plugs and coil pack but it's still misfiring, any ideas what's next?

 

[SenorNoob]

If it were an earlier model with batch fire, I'd suggest bad wiring on injectors for that side. Since it's not it'd have to be 3 separate failures which seems... unlikely.

Any chance the upstream O2 is giving wrong enough readings that the PCM is adjusting fuel till it misfires?

I've had lots of bad new spark plugs lately. (Granted all NGK on powersports applications.) IDK if I'm just lucky like that or if manufacturing has gone that far downhill.

Did you set gap before installing? That can make a huge difference. Especially if you set it to the wrong spec. (Like say the 3.0 or OHV specs if you have a SOHC.)

 

[TJS1011]

I did gap the plugs to between .050 and .055, which is the supposed spec for that engine. This is a weird issue in that it was so sudden. I drove to a friends house and the truck was running fine. Visited for a couple of hours got in to go home and immedietly upon driving out of his driveway it started misfiring and the transmission was clunking bad when shifting. Got home, hooked up the code reader and found P0301, P0302 and P0303 along with a P0102 for low input MAF sensor. Strangely there was no P0300 which is a multiple misfire code. Also, the engine won't rev past 3000 rpm, which if my memory serves me right is the computer shutting it down. I'd appreciate any ideas.