2004 has been 3.0 with 195,000 miles. Runs perfect above 2500 rpms and before engine warms up. It has misfire on #6 and plugs, wires, and coil has been changed. It idles rough after it is warm and has a loss of power when first taking off. You can run all day long at highway speeds with no problem. A mechanic said that if the exhaust valves have recessed someway they or it could be shimmed. Is this true?

 

Recommend you perform a leak down test, my 3.0 is showing the same symptoms and turns out the intake valve is leaking on #6. Got rebuilt heads on the bench waiting on an opportunity for a top end overhaul.

 

Thank you. Did you have the original heads rebuilt or buy other ones?

 

I bought rebuilts to try to get it done quickly, I drive my ranger daily. my symptoms were worse during colder weather, it would throw a random misfire on #6 every once in a while during the winter months but would settle out and no codes all summer.

 

Don't rule out a dirty or malfunctioning fuel injector... you could switch it around with another and see if problem follows, or just replace it. Current mileage would justify it.

 

I had a #6 misfire on my 3.0 ranger, daily driven never sat, always maintained and regular fuel filter changes. I had tested plugs, wires and coil pack except for the injectors. I decided at over 200K miles I need to service the injectors. I sent them out for service and #6 was not firing. After the service the truck has been transformed. Check your fuel injector(s), If it has never been serviced it's worth the $20 per injector to service them. Good Luck and keep us posted.