My dad has a 90 Formula with a 350 ZZ4 Crate motor with SLP runners, lingenfelter intake, edelbrock headers, and a Flowmaster catback. Lately when the engine is warm it has begun to ping, miss, and sometimes backfire under light acceleration.

To date I have checked the timing (6 degrees), changes plugs, then changed the gap from 35/1000s to 45/1000s. Then I replaced the EGR valve and finally disconnected it. Nothing seems to help. Any ideas?

 

Try checking the firing order, and make sure that all the plug wires are actually firing. Also I thought that 10 degrees is only if you have a mechanical distributor, I thought the TPI setting is 6* with the tan/black wire unhooked.

 

Check the ignition things first, especially look for carbon tracks in the cap or other sources of cross-firing.

If you don't find anything wrong, do a compression test; pay particular attention to cylinders right next to each other with low readings. I'd be most inclined to suspect from your description that both #5 & #7 will come out with low numbers.

Leave the timing alone. A properly running motor won't just up and develop these symptoms, and it be the ignition timing jumping off somewhere. If it ran good before with it at 10°, then whenever you fix whatever broke, it will run good again; and twiddling the timing won't fix the broken thing.

 

Sorry for the misinformation, but the timing was set a 6 degrees before and after their were problems.

I was told that the mechanic did a compression test and that was fine. I can get the actual numbers soon.

My dad is going to pick up some octane booster tomorrow.

 

Skip the octane booster. That wont do much of anything. I second RB's notion of cross-firing. Like RB said, a motor just doesnt do that type of thing on its own. It has to develop a problem first. Its always a cause and effect situation for these type of things. Something goes awry and the engine lets you know. Even if the booster DID do something, it wouldnt be fixing the problem, just masking the effect. Either way, the cause is still there.