So last Saturday I picked up a 2003 Ford Ranger XLT Extended Cab w/ a 3.0L V6. I knew it needed work when I got it they originally wanted around, Has roughly 140,000 miles give or take on the clock so not too bad i've seen em with nearly double that.

Anyway It has a misfire on Cylinder 6 which is noticeable mainly at idle, CEL is on obviously. It flashes when the truck is warmed up if it's around idle. If I bring the RPM's up to around 1500 or so the light stops flashing. Engine has good acceleration theres no backfiring, no stalling, easily gets up to highway speeds with no issues.
When I did a compression test this is what I found..

Cylinder #1 - 200
Cylinder #2 - 170
Cylinder #3 - 170
Cylinder #4 - 170
Cylinder #5 - 160
Cylinder #6 - 91

As you can see Cylinder #6 is a bit low im guessing thats the cause of the misfire (I also took pics of the plugs). Truck does not burn any oil that i've seen so far, and it doesn't smoke. Did a vacuum test too. At idle the needle on the gauge was around 15-16 inHg and when I revved the engine it moved to between 19-20 inHg At no point was the needle steady (not really fluttering but just slowly moving back and forth). I don't see any smoke or feel any pressure when I remove the oil cap with the engine running so I'm not thinking its anything in the bottom end (at least I hope not). My neighbor thinks it could be a burnt exhaust valve. Haven't been able to do a leak down test to confirm that or not... Truck also has these codes. P0113, P0117. P0118. but those are all pending and so far not contributing to the CEL being on, I should also note that the temp gauge doesn't work, could be related to the P0117 and P0118 codes not really sure there, my main focus right now of course is the misfire and dealing with that.

 

The 3.0 got a reputation for having valve seat problems, so I would make a slight wager you will have to pull the heads. I think the seats eroded allowing the valves to 'sink' into the head more. I think above idle it was not noticeable.
tom