Ok I just got back from Iraq like month ago and I'm driving my car after chasing this bimmer on the freeway at like 120 MPH. Then I decide to see what my AF ratio is by doing some WOT runs in 4th then suddenly I lose power and the AF ratio is going crazy. So I pull over and bam sounds like I'm missing a cylinder.

I managed to get it home on 3 cylinders sux no power. I knew there wasn't a problem with the injector cuz I pulled the injector and didn't hare any noise change. and I'm pretty sure I"m getting spark cuz everything look sgood in that department. After like 3500 RPM the engine kinda starts running smoothy again and the engine starts dumping more fuel in like was WOT. my vacuum needle also fluctuates from like 15 to 19 hg.

Did compression test
260
260
260
30

Then I tried to ghetto rig a pressure tester and put the engine at TDC. The 1st cylinder holds enough pressure where my ghetto tester starts popping apart. Then I move to the 4th cylinder and I can hear air coming out of my muffler.

So I just wanna confirm if this means somethign is wrong with my exhuast valve on the 4th cylinder. I took the valve cover off and everythign looks fine so its gotta be in the combustion chamber. Could I have cracked my head also? probably not....

arrghhh damn head I just had new valve stem seals put in it like 5k miles ago. :( it so much work getting that thing off :(

Maybe you screwed your rings, dunno, but you def got something going on.

yeah I did dumped some oil into the cylinder and the compression didn't go up so that rules out the rings unless I have a hole in my piston I don't think its easy to melt a hole in a forged piston though O_o

maybe the valve seal???

Check the valve springs. You could have broken one. Burnt valves don't happen in an instant. Also the springs had to be compressed to put in the seals. and since you had the seals done about 5k ago, the springs sound suspect.

Originally posted by 96NTeclipse
Check the valve springs. You could have broken one. Burnt valves don't happen in an instant. Also the springs had to be compressed to put in the seals. and since you had the seals done about 5k ago, the springs sound suspect.

if it was a valve spring the cam would still hit it and you would hear a metal on metal sound or if the cam isnt' hitting it the valve would probably fall and be hitting the piston. pull the valve cover tomorrow and see what you can see i guess.

Not necessarily.. we have a dual spring setup. the inner spring could hold enough tension to keep valve actually working. But without the help of the stronger spring, the valve would not work well at all.

EDIT: I take that back.... I don't remember if we have dual springs or not. I did not have a compressor that would allow me to replace mine so I got a machinist to do it. And I never thought to look. Regardless, broken valve springs do not always result in the valve contacting the piston.

hmm took the valve cover off earlier today and the valvetrain looks fine to me. The valves go back fine. As far as I can see though. How can I tell its the spring besides just looking at it? If it was the spring the rocker would be loose?

So burnt valves don't happen that often?

i dont know what the other guys is talking about. you can melt a valv eif the temps go high enought. same with piston. if the spring is broken you will know it.

Well if you dont want to pull the head then remove the intake and exhaust manifolds and rotate the motor until both valves are closed on that cylinder. Pour some water in one of the ports and look in to the cylinder from the spark plug hole and see if any water gets on top of the piston. Do that with the intake and exhaust ports one at a time. You dont need to pour much in there either. When you finish, leave the plug out and turn the motor over with the starter long enough to get the water back out. If you see water getting on the piston then you have a bad valve or valve seat. Also pouring oil in the cylinder does not always seal the rings, i've done the same thing and had the same results, then pulled the piston and have the rings fall out in about 20 pieces.

I fried a valve and it sounds like the same symptoms that I had. Do a leakdown test and see what you come up with.



Nice to see ya still around
Nick
97RS

Well, it sounds like he did a leakdown test. After all, how else would he know that there was air coming out of his muffler?

yeah I'm about 80% sure its a valve problem in the combustion chamber. Or at least a sealing problem. I found out I had a proper pressure fitting and tried it on #1 and held 50 lbs no problem. Then I put it on #4 and 50 lbs of air straight out the exhuast.

Tommorow I'm gonna pull the head I got it nearly off today but I have to go pick up a turbo L28ET for my 280Z ^_^ So tommorow for sure I'll know wats up.

right on man, keep us posted

Nick
97RS

well its just as how I expected well I didn't expect it to be this bad but pretty close :P Just took the head off about an hour ago and the valve was how your say burnt.... nah more like 1/8ths of it disentegrated! And where is the piece that cracked off? somewhere on highway 280 or its probably been crispyfied by my catalytic converter. Luckily I checked out the cylinder walls and the bottomend is unharmed. :) Good thing I didn't have the turbo installed O_o

Well what's the lesson learned here is when you build a highmileage engine into a race engine you rebuild the whole top and bottom end. O_O