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Discussion Starter #1
thanx in advance for any help. I have a 69 Z28 with a zz4 350. problem is that it fires into the headers from cylinder #8. if I pull #8 plug wire it stops the misfire so I know it's #8. I have new rotor and cap and plug wires since problem srarted. Have adjusted the hydraulic lifters. compression is oK, timing is OK. had heads ported/polished etc. last summer and it ran fine after that. how do I diagnose a bad hydraulic lifter or a valve that is hanging up on me?
 

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How do you know it is misfiring into the header? Is the header glowing?

It could be that your mixture is too rich...
 

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Discussion Starter #3
I can feel the blast of exhaust when it misfires coming out of the headers. when the engine warms up the misfire substantially deceases it's frequency
 

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It could be a sticking lifter or valve. When the engine is cold, the lifter piston should move when pushing down the pushrod. It should move 3/16" to a 1/4" freely. If it checks out good, then try pushing down on the exhaust valve stem and feel for sticking/binding on the return. Take a piece of flat bar, measure the distance from the valve tip to the rocker stud. Drill a 7/16" hole in the flat bar where the rocker stud measurement is. Now use the flat bar as a lever setup to depress the valve stem. Be careful to press on just the stem tip and not the spring retainer or you'll end up removing the head to retrieve a valve.

Just my .05 worth

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67 Camaro LS6 454/TH400/12bolt 3.73

[This message has been edited by cardude (edited 03-12-2000).]
 

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I thought ZZ4 motors came with roller cams??

I would make sure the timing is correct.

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68SS ZZ4, 4sp T-10, 12 bolt, getting painted

78Z28, 330hp vortec, TH350, 10 bolt (just finished)
 

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ZZ4 crate motors do come with hydraulic roller lifters. It's NOT a worn cam lobe because GM uses billet steel roller camshafts.
 
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