2009 Ranger, 4wd, 4.0, 120,000 miles.

I got a check engine light which indicated a miss on number 5. The truck was running fine so I decided to change plugs and wires on the weekend. Within a couple of days, the truck was obviously missing. Changed wires and plugs and the problem seemed to be worse. Changed the coil but the truck is still missing badly. I have checked and double checked that the firing order is correct and that all wires are in place and properly seated. Compression test showed 115 pounds as an average wthl all cylinders within a few pounds.

Not sure where to go next. Any suggestions?

Ignition module, how to test?
Clogged injectors, how to test with basic tools?

 

Might I suggest u pull the plug and check it? Double check your gap and for cracks in insulation....hell, try swapping the plug out with another cyl to see if the misfire moves to other

 

I have all new plugs in the truck.

 

Ok, doesn’t mean that the insulator couldn’t be cracked r that the gap is correct.........case in point I chased a random misfire with my trk for a period of time....this was after doing a complete tune up all new new coil,plugs and wires....well line and behold the misfire turned out to be a couple of plugs that I had gapped just touch too wide.......

 

Good point, but I think I found the issue. When I checked compression the first time, I must have forgotten to bleed the gauge and got 150. Just did it again on cylinders 4, 5, 6. I got 160, 90, 150 respectively. The truck has never burned oil so I suspect something in the top end. Won't know until I get it apart. Beside bad valves, is there something that is common and not expensive with these trucks?

If I do have bad valves, can anyone recommend a good shop for reman heads?
If I redo the test on 5 again with a few squirts of oil in the cylinder, increased compression will point to bad rings, right. However, if the compression remains low, that will indicate gasket, valves, etc.

The new plugs have about 60 miles on them. The plug from 5 came out and appears to be getting hot on one side.

 

Does it misfire at idle or when REVing engine in neutral ?

Or does it only misfire under load?

Does it misfire cold or only after warm up?

115psi on compression test is quite low for 4.0l SOHC, would expect above 150psi even in Idaho elevations
But if they are all close then could just be the gauge.

And #5 wasn't slightly lower than the rest?

Ignition module is part of the engine computer, that started in 1995 Rangers

You could run a can of Seafoam or similar injector cleaner in the gas tank, that cleans the injector tips.
Should do this once a year on fuel injected engines.

Could be a lower manifold vacuum leak.

You can get Bluetooth OBD2 readers, $20-$40
You use a smartphone or tablet with blue tooth as the display, APPs are free or $5

With these you can monitor LIVE DATA from the engine, fuel trims can tell you if one bank(side) of the engine is running leaner or richer, leaner would indicate a possible vacuum leak on that bank