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..

Tried posting this the other day but I don't think it went through.

 

I’m fairly new to Rangers but I am dealing with a similar problem with my vacuum. I checked vacuum and then did a compression test and then a leak down test. My results may help bring some clarity to your issue. I got 165 on cylinders 1,2 and 6 and 150 on cylinders 3,4 and 5. At first I thought that’s not too bad and on an engine that’s running well I would have ignored it. However since I had a rough idle and low power I did a leak down test. The only cylinder that failed was cylinder 4. Air coming from exhaust and oil fill. Now some air coming from oil fill is normal. I pulled that head and turned it upside down and propped it up level and filled the domes with water and cylinder 4 and 5 started leaking from the exhaust. Mind you cylinder 5 passed the leak down test. So now I know I have two burnt valves. I am willing to bet money that cylinder 3 will leak too even though it passed the leak down test. So even with 150 PSI I’m having significant exhaust valve issues. Mine are probably made worse by the fact that it’s multiple valves. The reason that I suspected exhaust valves is because when I put a piece of paper against the tailpipe it sucked it up and pushed it away in a quick and strong flutter. I would definitely suggest the leak down test however it’s probably enough to redo the compression test and add oil to the low cylinder and if it only goes up a few psi then it’s more than likely a valve issue. If it goes up to spec then it’s a bottom end issue. Also this was my first time removing a head (I have the 3.0 Vulcan) and it was very straightforward.

 

I just checked the date of your original post. I think I need to start doing that first haha. Hope you got your issue worked out.