IRONFIST

Ok I've had a miss on #5 ever since I missed a shift and rev'd up too high.
I had bent pushrods, replaced them, but still had a miss.

I did a compression text on #5 and it had compression, was in the "green" part of my compresson gauge. But this weekend, I took the time to check the compression of the other cylinders, and #5, although it has compression, has considerably less then the surrounding cylinders. This would explain the missfire...
How can over reving the engine cause a misfire, I'm thinking a bent valve?
Ideas? Heads are coming off tonight, what should I look for?

shtnfrds

iTrader: (1)

look for a bent valve, maybe a cracked spring? dunno.

99RTA

iTrader: (-1)

A leak down test will show you where the loss is.

TooLateVTEC

iTrader: (2)

Take both rockers loose on that cylinder. Then make a fitting to put into the spark plug hole and put compressed air to it. If you hear air leaking its probably a bent valve.

IRONFIST

If, some how ( cross my fingers ) the rings are gone, or something to that affect would it not still make a noise?

How do I make this fitting?

vettenuts

iTrader: (4)

Once you lose valve control, bent valves will likely result. I would plan on head removal.

IRONFIST

I have a set of 243's to put on anyway.. I just hope it's valves and nothing internal.

vettenuts

iTrader: (4)

Your indication is low compression as opposed to no compression. Likely an eyebrow in the piston but it doesn't sound like short block issues from your description.

Zero4488

iTrader: (10)

I had a simillar problem on my car...started as a miss only at WOT that would come and go...then became a miss all at any rpm in any driving condition that would come and go....and now it has become a completely dead cylinder all the time...#7 seems to be the one that is affected on my car....any input guys? and btw I'm sorry for hi-jacking...

-Dave

poolshark021

iTrader: (8)

The fact that your pushrods were bent is a giveaway that there was piston-valve contact. The valve could be bent just a hair and not quite seating properly, giving you lower compression readings. The only way to know for sure is to do a leak down as mentioned earlier or pull the heads (which you are doing anyway). I would be suprised if it was in the lower end.

poolshark021

iTrader: (8)

You should start another thread as your problem seems different than OP's. You should start by checking the plug, injector, compression and go from there. Kind of sounds like an ignition issue to me...

00pooterSS

iTrader: (40)

exactly. look for a bent valve, should not be bottom end related. best way to notice a bent valve is to look at the outer edge of the valve versus the valve seat, look at is as two circles one inside the other, the bent valve will lean toward the edge of the seat. there should be even space all the way around the outer diameter of the valve head to the valve seat outer circle.

Zero4488

iTrader: (10)

I've replaced the plugs, wires, injectors, coil packs...everything possible on the outside of the motor....

99RTA

iTrader: (-1)

cylinder number 7 runs lean in these cars...it may have broken rings or worse. Its common..thanks gm..

IRONFIST

You guys rock...

I got almost all the bolts off, just have the little ones under the intake, and the one under the valve covers closest to the firewall to get out.
So hopefully I will know tonight.
I guess I never thought about it, but a bent pushrod would have to indicate piston/valve contact....

Hopefully I'll pick up some ponies with the 243's as well.

00pooterSS

iTrader: (40)

cool let us know, and you will pick up some with the 243's, if they are vette 243's the valve weight being lighter by itself will help you keep from floating the valves again and causing damage, but the head is also a superior design as far as flow characteristics, plus it has a smaller chamber so you will pick up .5 on your compression ratio just from stock to stock heads. If I recall it has a quench area or better quench than the stock LS1 heads so that cuts down on detonation as well. Those heads are all kinds of good. BUT if they are vette 243's the valves are .030" longer so you may need a shorter push rod, not positive on that since mine are still sitting in my garage floor.