4 cylinder 3.0L

[Rulebreaker]

Brought my 9th RBV home this past week and it's a very high mileage 99. It would start right up but had a rough idle and low power. Pulled the plugs and 2 of them were black so check compression and 4 and 5 were deader than a door nail. The other 4 were 70-100. Pulled the head on the dead side and I really though I would find a blown head gasket between the 2 cylinders but I really dont see anything out of the ordinary other than a color difference between the good and bad. I was hoping it was just a head gasket so i could drive it while I prepare the replacement engine. Any thoughts? Valves? Rings? Cracked head? Puzzles me to have 0 psi? The needle wouldnt even wiggle on the gauge. RB

 

[stmitch]

Valve guides have been an issue I've seen. Could be a cracked head, but it seems unlikely. How high is the mileage? The compression numbers for the other cylinders don't really seem to healthy to me either, so it may be time for a rebuild.

 

[RonD]

Cracked head would generally have some compression so would a blown head gasket.

Even bad rings would show some compression, what do the cylinder walls look like?

Valves not seating or burnt would give 0 compression.
Haven't heard of it on the v6's but the Ford 4 cylinders OHC could get "tuliped" valves.
The valve cups out at the seat(tulips) so valve stem sits higher, this prevents it from closing all the way, but with hydraulic lifters this would be a lot of cupping.

I would pull the valves.

The other cylinders at 70-100 are very low so maybe cam timing is off, loose timing chain, I would expect above 150psi
I would test that gauge on another vehicle just to be sure it is reading correctly.

 

[Rulebreaker]

I filled the intake ports with the parts cleaner and it held the fluid so i filled the exhaust side and it ran right out so I looked at the exhaust valves and they look to small and set way down in the seat. I'm going to say they are cooked. Are the heads interchangeable left to right? I have another set of heads but the PS head is in better shape than the DS so I'd like to use the PS head on the DS. The truck has 260,000 on a speedometer that dont work so who knows how many miles it has.

 

[RonD]

Heads are not bank specific, so can be swapped around.

"Pinging" causes cylinder overheating and over time bad exhaust valves, so this could have effected all the exhaust valves on both heads, so check them all.
Intake valves are cooled a little more by incoming fuel/air so tend to survive higher cylinder temps.

 

[Rulebreaker]

Good to know on the heads. The coolant has some kind of bars leaks crap in it so I'm guessing there was some overheating issues in the past as well. That might help with burning up the valves as well. I really only need this engine to run for a few months while I overhaul the 2.3L I'm putting in this truck.