Just tore down my 99 f150 with 5.4 found both the intake valves#2&3 cylinders burned, also heavy damage to plug electrodes, does anyone know what the root cause of the burned valves is. I notice they both get air from the same side of the intake plenium, found no hose cracks.

 

what shape is the exhaust in? Would a manifold leak cause this? Or what about running duals without backflow mufflers? Just off the top of my head, maybe these things wouldn't bother these new engines.

 

tanks for thoughts, exaughst is stock in good condition, havent found a manifold leak source yet. hmm!

 

Running very lean in those cylinders would do that... clogged injectors? Get them checked, post back with info...

What is the color of the intake runner in the head in those cylinders compared to the ones next to them? Any marked difference in color?

How much carbon was in the cylinder area of the head and on top of the piston? More, less than the others?

Could have been pinging/detonating in those cylinders, but if it was that bad, you would have heard it.

 

Just noticed you specifically said intake valves were burned. A big exhaust leak would cause the exhaust valves to burn, not the intakes.

Again, clogged injectors, vacuum leak (around injectors possibly, or right at the intake-to-head interface)...

 

Thanks for info, looking into intake plenum and find a fairly uniform dark brown deposit possibly slightly darker in the inner most ones, the intake gaskets looked good, head gaskets as well. Unfortunatly i pulled off and mixed up the injectors, however i did check all the inlet screens and found them clean. also little or no carbon bildup in head, valve or pistons, but slightly darker in the burned valve cylinders. Is it possible that the computer could have leaned thease cylinders and not others?

 

The computer is not setup to lean or richen certain cylinders.

All it might do is modulate one bank - as in 1-4 or 5-8 - because it has an O2 sensor for each bank. But I don't think it even does that.

I'd still get the injectors cleaned and tested - could be that you find 2 that are abnormal.

Weird...

All I can say is, once you get it back together, check the plugs for color every month or so, before it burns out more valves.