I'm having persistent misfires on 4 6 and 7 and have reason to suspect the valves. But I removed the intake to swap coils and my wife noticed that the 4 6 and 7 intake tubes were clean. No way I cleaned three and left five dirty. Could this be bent intake valves?




That picture isn't great. But 4 6 and 7 tunes are clean. All of the rest have old oil on them. Since my valve covers don't vent to the intake anymore, something has cleaned those tubes. If the intake valves don't seat properly, then exhaust gas and or gas could be cleaning them.

ANY other theories?

I'm asking because I am about to swap the heads. But if there is a better theory I'm all over it because I'd rather save the head gaskets and work if something else might work.

 

I'm still thinking no on the valves because your compression test would've been way low. I think you should pull the valve covers and check the cam. Make sure no lobes are rounded off by making sure all the rockers extend fully when they're supposed to.

 

I'm doing that now as I work my way down. I recall, a few days ago, turning the engine and seeing the rockers move on all cylinders but I'm getting that desperate feeling after having tried so many things. I'll try them all again. I'll just pull the fuel pump relay and turn it over. But if I smell gas in those tubes from lingering pressure Ill think the valves may be screwed.

 

No wait. You're saying the cam might be keeping the valves open. Yikes. I wouldn't have any clue how to differentiate between bent valves and bad cam except by removing the heads and filling the with water.

 

Maybe there is something wrong with the lobe grind and the intake valves on 4 6&7 are closing to late and you are pushing some of the fresh charge back into the intake washing the intake runners clean?
Are you sure your timing chain marks are correct, not a tooth off?

Which bore did you bend the rod on?

 

I pulled the valve covers and turned the engine whole watching the rockers. They all go up and down. So I pulled the head on the passenger side (4 and 6) then filled the exhaust side with water, and the passenger side with water. Not a drop out of any of the valves.

Number 8 had the bent rod and broken piston. It has good compression now.

I also filled the cylinders with antifreeze (from removing the heads) the level hasn't dropped in any of them for an hour.

Stumped.

I'm going to be so pissed if it is the cam.

I'm positive about the timing chain. I turned the crank sixteen revolutions and made sure that the marks were perfect each time, before I put the cover on.

 

I can only assume that a bolt fell down the intake and is now in my catalytic converter.

 

Which piston is that?


Did you do a compression test? A compression test should have found that.


Why are there other cylinders not firing?

 

Crikey.

So a bolt was flying around in there, managed to find its way past the exhaust valve and moved on.

Or disintegrated and moved on.

Kinda incredible.

Can you match the thread size from those imprints to narrow down which bolt it is?

What a find.

 

Damn, that's rough. Still, I don't think that would cause a misfire unless it took out the spark plug or bent the valve. Much less on three cylinders. Still, its good you found the issue. It didn't scar the piston wall too badly I hope.