98 350 vortec. ran compression check. all were 160-170 except #3, which is 120. what throws me off is that the #3 and #5 plugs are brand new, 250 miles on them and they are covered in ash like soot, wet. #5 cylinder came in at 160, which seems ok to me, but how can two brand new plugs get so fouled up. the rest of plugs have only 1000 or so miles on them. and look great. rig just went thru the mfi spider conversion, all injectors are seated good. if 7 cylinders show good compression, one cylinder shows low, yet two plugs are gunked up, ideas? could it have vacuum leak? or worse, head gasket? ain't got much money left to throw at this thing, or time.

 

pulled the drivers side head off, found that head gasket appears to be good. didn't seem like it was blown out. but there is quite a bit of carbon build up on top of #3 and #5 pistons, as well as quite a bit inside the combustion chambers of those two cylinders. this leads me to think that maybe the valve stem seals might be leaking. valves on just those two cylinders have some carbon on them as well. does leaky stem seals make sense in this case?

 

anyone ever had valve guides go bad without burning oil?

 

Haven't seen it personally, but I've heard of it...

 

thanks hoss. tryin to figure this out. bout to shoot the truck, set it on fire. aaaarrrrrgggghhhh!!!!! can't get much help. general census is put it back together with new valve guides, see what happens. guess that's bout all i can do.

 

Shooting it, doesn't neccassarily kill it... Ask my 89 Silverado...

 

well, if i can't figure this out for another $100 or less, i'm screwed.

 

how do the intake manifold ports compare to on 3 and 5 to the rest of them?, thinkin leaky injector could be flooding those to holes

 

injector unit is brand new. i bought the mpfi conversion, which eliminates the problematic stock poppet style. i can't imagine that the #3 and #5 injectors on the new unit are faulty. i've heard of coinicidence, but the same two new injectors being bad? i've come to suspect valve guide seals. some research had led me to believe that they could be leaking so much that the two plugs foul out fast, before i can even notice any smoking. gonna change them out, clean everything, put back together, cross fingers i guess.

 

if it helps ill helps ill bring over some guns and shoot it with you