Just figured I would post this because I feel that its kind of rare and is probably overlooked a lot because of that. A 98 Blazer 4.3 with a burnt exhaust valve. The story...Picked up this 98 Blazer 4 door 4x4 for my Daughter, her first car, body and interior in great shape with 190k miles, Dads a Mechanic so she gets em cheap...but broken, $500 bucks, dead mis on #5, guy says hes pretty sure it had low compression on that cylinder, drive it 2 hours home knowing I have a pair of heads if its a valve and I have my Daily Driver blazer I can yank the motor from if all elese fails and then it would give me a good reason to small block that one. Anyway, I have the 17 year old Girly Girl Daughter helping me and over the course of 2 afternoons of teaching and teardown we get to the drivers side head. I'm still not sure why im surprized because I found exactly what I assumed Iwould find, sure enough, #5 exhaust valve has decent sized hole in the face, see pictures. I guess I just dont recall these engines having may valve issues? This cylinder was only producing about 30 psi on the compression test. What I find most intersting about this job is that I can tell someone has been inside this motor somehwat recently, maybe its not the factory engine or maybe the heads were replaced with some cheapo parts store brand re-mans that were built with chineese valves, but there are other things that make me wonder too, its been put together with same set of severe duty fel-pro gaskets I ordered for it, its got 190k and the rear main is bone dry, in fact, the entire oil pan is bonedry, not even oily residue on it. Sometimes I wish a car was like an old guy that could sit and tell you stories about the major events in its life, instead they tend to be more like a minor with a sealed criminal record or a 2 faced bi-polar compulsive liar.....but I love em anyway.
Sorry for the rambling, just wanted to add a solid diagnosis to the page for anyone in the future having problems with a dead misfire and low compression on one cylinder. I guess nothing is ever for sure but a good visual is always helpful.
The best part of this whole job is that it's only going cost a set of gaskets and fluids, the heads I had on hand were given to me a couple weeks ago by a friend, 10 years ago when he worked at a dealership he snagged these off a 20k mile motor that had spun a bearing and came in with a light knock, they sat in his garage til now and right after he gave them to me I snagged this blazer off craigslist that just happened to need them, good luck and good timing I guess??
I may post some more pics later, was surprized to find a set of permadry plus intake gaskets that looked like they've seen better days, I thought they were indestructable.

Sorry for the long post, hope this helps someone!!

 

I would hope that the missing piece of the valve probably went out the exhaust.

 

If I have P300, P302 problem on OBDII (cylinder 2 maybe?) i have to do what you did? I tried everything (rotor, cap, wires, sparkplugs, inyectors clean, gas filter)?

 

Not that rare. I have 2 engines that had valve problems in cylinder #5