i blew up my other motor so i got a another block and had my performace parts put back on the new block. i added the afr heads which werent on the old motor. all other parts listed below were installed. i got my car back and it ran bad and was just as fast as it was before i had it rebuilt. thats with adding the afr heads so i new something was wrong. the put it on an engine scope and short out each cylinder and found out that the #8 one is not firing. what could cause this because they dont know right now.

 

Motor needs 3 things to run:

1. Fuel
2. Spark
3. Compression

Work BACKWARD through that list when diagnosing problems.

1. Compression test. if it ain't got squeeze, it ain't gonna fire. Usual culprit- valves adjusted down so far that one (or more) of the valves is being held off it's seat when it should be fully closed, allowing compression to escape.

2. Run a test to see if there is actually a spark coming down #8 plug wire. Check for an arc to ground with the wire pulled off the plug and held near a convenient ground.

3. If you run a carb it's a guarantee that you are getting fuel to #8 or the carb wouldn't be feeding 1-7 eiither. If you have fuel injection it could be a dead injector or one that is clogged with dirt or leaky.

 

If you're getting a spark from all the cylinders except #8 then it has to be the distributor cap or the plug wire. A good way to check the wire is just switch a working wire onto the #8 position on the cap and ground it to test for spark. Go ahead and take off the cap and see what kind of shape it's in too, ie. check for corrosion on the contacts. New distributor caps aren't too expensive.

This is assuming you have an HEI ignition. If you're on points, good luck...

 

update i was watching the guy troubleshooting my car today. he hooked up a compression testor to the #8 cylinder and it didnt have any. what he believed was causing this was the crane rocker arms. he thinks he tighten them to tight and they were holding the valve open. so i watched him retime all the valves and tighten them to a quater turn. he ran out off time so i will find out monday if that was the cause.

 

This guy doesn't sound like he knows what he's doing when it comes to engines. First off, if the number eight isn't getting a spark, it doesn't matter if there's compression. Secondly, are these hydraulic or mechanical lifters? If they're hydraulic, he should be tightening them to zero lash, then a 3/4 turn, not a 1/4 turn. If they're mechanical lifters, then you'll have to check on the amount of proper valve lash, but it sounds like they're hydraulic by the procedure.

If the valve was staying open you're lucky the piston didn't smack it and snap the valve stem. Do yourself a favor and find another mechanic. Just MHO...

 

If indeed there was no compression in #8 when tested
then it is likely that a valve on that cylinder is too tight and open all the time. If it's a hydraulic cam simply bump the motor over
till that valve is closed( spring all the way up and readjust it
for 0 lash. Do the same for the other valve. Start the car and
adjust the valves running on that cylinder. If it is now running on all 8, readjust all the valves for proper running lifter preload.