I need some help on diagnosing a problem that I'm having with my 160,000 mile 3.0 V6 automatic Ranger.
I started to get a noticeable misfire and, after more miles than I expected, the CEL finally came on.
Pulled the code: P306 - #6 misfire.
OK...simple enough. I was getting close for a plug & plug wires change anyway.
Plug #6 was a little wet and the porcelain was dark....not light beige like the other 5 plugs.
After installing new Motorcraft plugs & wires I still had a #6 misfire and, eventually a P306 CEL code.
Installed a new coil pack....same problem....misfire on #6.
It starts up and has a slight miss which goes away once the truck is warmed up, but under heavy load it misfires pretty badly.
Then I checked the coolant and it was very low plus was rusty brown. (I change the coolant regularly and it has never looked this bad before.)
Refilled the coolant and checked after a few trips:
Uh Oh....The truck is consuming coolant, but there is no smell, no leaks, no white smoke from the exhaust.
Pulled #6 plug and inspected....it doesn't look too bad and is not wet.
Next I did a compression check and all the cylinders read between 144.0 and 160.0.
Cylinder #6 shows a healthy 154.0....WTF!?
I was certain that I had a cracked head or blown head gasket.
Before I pull the top end down what else could cause this?

 

This happend to my 02. Possibly bad valve.