I had a misfire that started with cylinder 4 and now it comes up on obd as cylinder 4,5,and6 misfire and sometimes it just says cylinder 4. I have tested all the vacuum lines with a smoke tester. Changed the coil pack,injectors,wires,plugs,crankshaft positioning sensor,and the coolant temp sensor. I have also used cata clean. I can not figure out what else it could be and am totally lost on figuring it out. Hoping someone would possibly know or had this same problem and was able to fix it.

 

When there is a misfire, first test you should do is a compression test
Easy enough to change spark plugs, and they do wear out, but after that do the compression test

Compression is either good or bad, so best to take it off the table or find out if it is the problem so you don't waste time and money on non-fixes

Cold engine
Remove all 6 spark plugs first
Then test each cylinder, one at a time, and WRITE down results

You don't mention the year of Ranger or engine model, but a V6 should run 150psi average for static compression

 

I didn't realize I forgot to add the year and engine size. But it is a 2003 with a 3.0 flex fuel

 

And also if the compression comes back different on 3 out of 6 cylinders would that mean the piston rings are bad or could it possibly be a valve or both?

 

Won't know until you do a dry compression and then a wet compression test.

 

Most common compression issue with any engine is burnt exhaust valves, this can happen to any engine at any time and to any number of cylinders
WET and DRY test tells you if its rings or valves

Rings usually last 400+ K miles in engines made after 1980 or so, just better materials