2.5L ('98-'01) 2000 Ford ranger 2.5 misfire

[Rubenbmx183]

Hey guys so over a month ago I turned on my 2000 Ford ranger 2.5 and it was just misfiring so I changed all 8 spark plugs and all 8 spark plug wires and nothing, I changed the coil pack closest to the back since there wasn’t spark on cylinder 4 and nothing. So I check my catalytic converter after a night drive and it was red as a tomato so I cut it off and welded and it did nothing…. My mass airflow sensor looks new but just in case I cleaned it and still have the same misfire…… I put a scanner through and get codes, p1506 (IDLE AIR CONTROL OVERSPEED ERROR) I also get p0304 (CYLINDER 4 MISFIRE DETECTED) and the last code I get is p0171 (SYSTEM TO LEAN BANK 1) I TURNED OFF THE CAR ONE NIGHT COLD AND TURNED IT BACK ON RIGHT AWAY AND THE MISFIRE WAS COMPLETELY GONE UNTIL 5 MINUTES LATER AND THAT LUCKY MOMENT NEVER CAME BACK WTFFFFF. Also sometimes when in neutral when I rev the engine the misfire is gone but once you put it into gear and start rolling the misfire is back and most of the time now even just revving it you feel the misfire… What do you guys think this misfire is?

 

[Douginator]

A gas engine needs 4 things to ignite: fuel, air, compression and spark. If the misfire is limited to one cylinder then you don’t have a problem with air or mechanical timing. The fact that the cat was glowing red means you have unburnt fuel entering the exhaust - due to the misfire. Which means you don’t appear to have a fuel delivery issue. For the next steps I would pull both #4 plugs and have someone hold the ground electrode against the head while cranking the motor. You should see white spark on both. If that is good then you need to check compression on that cylinder. It’s very possible to have a dead hole on a single cylinder, in which case you will need to do a leak down test. You may be lucky and only have a burnt valve in which case you only need a head

 

[Douginator]

I’ve also seen where a vacuum leak has caused a burnt valve over time on a newer Outback. Funny enough it was also cylinder 4 that lost compression. Your lean code, paired with the idle over speed code would suggest that a vacuum leak has been present for some time. You should be able to hear unevenness when cranking if there’s low compression though. It is also possible for damaged wiring to exist between the PCM and the rearward coil pack if there is no spark on just that cylinder.