Years ago I helped a friend with an engine that was exhibiting the same symptoms.  It was difficult to set the timing where it idled on its own, and always had a 2 or 3 cyl miss. He futzed with it for weeks, and finally implored me to make the hour drive to help him. Took me about 5 minutes to find it:


He had been given a distributor for a V6 engine.  There were only 6 firing points on the rotor/stator. A V8 engine needs 8.  No wonder it ran "funny".

That IS funny! I'll bet he was PO'ed that he had been given the wrong distributor!

Almost sounds like the new cam has the lobes in the wrong location or something.  Build for an engine with a different firing order, maybe?  That would be a reason why compression test is good, and all other components appearing to be working properly?

Which specific 3 cylinders are not firing?
Are those 3 cylinders completely dead?
Does it sputter/pop/backfire/fart/belch?
Are the plugs on those 3 cylinders fuel fouled, or clean?

Depending on the answers to the above questions, I would be leaning towards an ignition issue, assuming the compression is right in all of the cylinders. The pole piece/pick-up coil in the distributor could cause goofy stuff like this, as could the ignition module itself. I have also seen HEI rotors that would kill some cylinders, but not all.
And...."new" don't mean JACK....ever had a new light bulb that blew as soon as you turned the light on?
It may well turn out to be a problem with the cam, but if so, it should be backfiring or something, and it would have to be an even number of cylinders not firing, if it had the incorrect firing order. I wonder if he wound up with a cam for a Marine application? Some marine engines run backwards, and the cams are ground accordingly, but the teeth for the distributor gear would be "correct".
This is one of those absolutely frustrating situations, where you've checked everything that makes sense to check, but there's no hope in sight. That's when it's time to start checking stoopid stuff...like plug gaps.




|UPDATED|8/3/2012 10:02:55 AM (AZT)|/UPDATED|

I work on boats and yachts professionally. Have been for 30+  years. "Reverse rotation" camshafts that are intended for use with a timing chain (oil pump and distributor turn in standard CW direction) change the firing order for all cyls.

For a Chevrolet (big or small block) the reverse firing order is 1-2-7-5-6-3-4-8.  Imagine the "1" at the right end of that chain, then read the order from right to left. Interesting, huh?  When I proof the firing order on a reverse rotation, I just follow the wires around the distributor CCW using the we-all-know-it 1-8-4-3-6-5-7-2.

They didn't install a reverse rotation cam in the OP's engine.  It wouldn't run. Because with a standard rotation starter motor, all intake events would occur on piston up-stroke,  and exhaust events would occur on the down-stroke.  Interesting out-of-the-box thinking, though.

|UPDATED|8/3/2012 10:01:59 PM (AZT)|/UPDATED|

Dave, I have to think out of the box...they won't let me in anymore.....

just recently purchased a MSD dist, cap put it on and it had a dead miss on two cylinders first checked that the wires were in the right place fine so I removed cap and found a hairline crack in between posts very hard to see, turned out all the lights so it was very dark and sure enough lightning storm, try it turn off all the lights in the your garage off and start the engine and look for lightning storm around cap if so replace it and it shought be ok. and like I said the crack was very hard to see the cap was probably dropped during shippment. good luck trust your gut and weed out the easy stuff first then dig deeper. always write down what youve done and trust your abilities.