Hello all. I have a 1999 ranger xlt which was showing a code PO306 misfire cylinder 4. Here is what we have done so far......NEW OEM wires - new motorcraft plugs - compression check (good across all cylinders) checked for spark at the coils by removing wires 1 at a time while running - lots of spark all over the lead. Still has a miss. Did NOT replace the coil packs as of yet as they seemed to be firing. Don't know if this has anything to do with the problem but the AC and heat started blowing out of the defroster vents. Looked under the hood and the plastic grey vacuum line is broken at the evap case and I cannot find anywhere that it would go. Going crazy in SC.....

PS...forgot to mention - replaced injector also on #4 Cyl - no change...

 

Welcome to FTE.

You've been busy on this one & have done some good trouble shooting, but I'm not clear on your P0306 code, I think you meant P0304, or do you have another, or more code numbers, if so, post All code numbers, as they can offer up good trouble shooting clues????.

With the loose vacuum line, you should have lean codes or corrupt fuel trim numbers too.

 

Thanks for the reply.....it was PO 304 miss in cylinder 4. Tried new coil packs over the weekend - no luck yet. Still has the miss. Almost ready to blow it up or crush it (lol)........ just cant figure it out.

 

OK, well other things can cause a miss, like an acting out fuel injector, or sticking or burned valve, so have a listen to the #4 fuel injector & valve area with a stethoscope, to determine if something sounds different.

 

My 99 did same thing. I replace all ignition parts to no avail. finally took to friend shop and he put it on the scope. #1 injector was intermitintly firing. I know you said you put new injector in #4 hole, but with out truck on scope you donot know if it is working properly. The money I spent for the shop made up for my time and money throwing parts at it.