2000 Ranger 3.0 misfire cyls 5+6

[wileyz62]

Hi All!
Want to say thanks for all the help TRS has given me with this project.First,heres whats been going on.Ive got a terrible idle.At cold start,not so bad.After a good warm up feels like a gasser with a lumpy cam.Ive got a cel that wont go away.The codes coming up are,,misfire cyl 5.misfire cly 6.Prior to these codes was a egr flow out of range.On the freeway at cruising speed,,runs fine.Misfire is only felt at idle and very low speed,then clears up as I accelerate.
Diagnostics have shown me this:
Spark plugs are clean,normal,,no fouling or smell of excessive fuel.
Plug wires,,good
injectors,,fresh rebuilt with good atomization.
The trouble is in the combustion chambers.Number 1 is the only cylinder reaching 100 lbs.numbers 5+6 are barely over 50.As I said,the rest are all over the scale.
This is what Ive attempted to correct it.
New cam and lifters,head gaskets.A good thorough inspection of the heads and hand lapping of the valves.
This only improved the compression slightly,say 20 lbs on 5+6.
This morning,hooked up compressed air to 5+6 and listened for leaks.I could hear air only from the tailpipe.
Added oil to those cylinders and got no increase in lbs.My conclusion,,the rings and cylinders are fine.The problem is exhaust valves.Even though I lapped them and convinced myself they would create a good seal.
Ive been told by 3 different head rebuilders that the problem is the exhaust valves.Specifically,the seats.That the 3.0 is very prone to this being that the factory did not use hard enough seats.My question is:Is this a common problem?Shouldnt the lapping have made a significant difference?When I did this work,the exhaust valves looked as clean as the intakes.Shouldnt I have seen some evidence of the seats being bad?Or the sealing side of the valve showing signs of not sealing?

 

[Rearanger]

I'd look at rings and or an oval cylinder wall(s). Perhaps the sound out the exhaust was air going past the rings on 5&6 and into the crankcase then up past the rings on the other cylinders then out the open exhaust valve(s). When you had the heads off did you mic the cylinder walls for roundness?

 

[wileyz62]

Yes,While the heads were off.I looked the cylinders over very close.Were in very good shape.Also.Before and after head removal,added oil to the low pressure cylinders and checked for an increase in lbs.Was no or very little difference.