3 weeks ago I developed a misfire. I changed plugs, wires and coil pack.

Truck ran amazing for 2 weeks.

Normally 19-21 mpg, I was getting almost 24.

Last week misfire bank 6 came back. I pulled the plug and it was oily. Put a new plug in.

10 minutes later, misfire bank 6. P0306 again.

Any ideas to offer?

O2 sensors replaced in the last 4 years.
198k miles and it’s never leaked a drop of oil.

 

Welcome to the forum

So the spark plug tip in #6 was blackish, sign of oil being burned?
Or just the threads were oily

You could try changing PCV Valve and make sure its hose is clear
PCV = positive crankcase ventalation
When engine is running it creates a slight negative pressure in the crankcase and valve cover areas
This helps prevent oil leaks and also oil from running down Intake Valve Stems and getting into the cylinders
So new PCV valve can prevent oil burning

Ultimately you should pull all spark plugs and do a compression test on the engine
This is a black and white test so once its done you can move on to spark or fuel/injector issues
But if #6 has lower compression then you will be wasting time and money on non-fixes in the mean time

 

Ron D, the threads are clean. The tip is oily and black. Brand new plug yesterday.

I have not changed the PCV, ever on this truck.

Put another brand new poug in this morning. Drive 25 miles, it ran rough but no CEL.

Headed out for lunch and CEL either on or blinks and code is misfire bank 6 again.

ive never done a compression test. Is there a tool or gauge that I’ll need to pick up?

Huge thanks for the reply Ron!!!

 

That reads like a leaking valve guide seal

Thing about #6, and #3, is that they are at the rear of the engine and engine is higher in the front
So all the valve train oil pools in the rear lower edge of the top of the head, and the valve springs and seals are on the lower edge of head, so if the seal starts to leak, lots of oil can come in on #6

I would try the new PCV valve

You test compression with a compression gauge
They come with a flexible hose that has 14mm and 18mm threads on one end of the hose, Rangers all use 14mm spark plug threads
Then a detachable gauge that usually reads up to 300psi

Gas engines are 150psi

But my guess is the #6 will have HIGHER compression that the others because of the oil, lol
But worth testing