I just finished installing a set of vortec heads on my 89 firebird. i had already installed a LT1 cam headers, exhaust, performer rpm intake, pulleys, coil, wires, and an openn element, as well as a thermomaster chip. before the heads the car ran great but now it runs very rough and at light throttle and full throttle it hesitates and starts to shake but smooths out at about 2300 RPM. At full throttle I can smell gas. Has anyone installed a set of Vortec heads on a TBI? Is the computer freaking out or could it be an ignition problem? A bad plug or wire perhaps. The tbi is stock except i have ported it and the fuel pressure has been turned up. Any suggestions would be appreciated

 

I'd start with mechanical things first. Re-check the valvelash, look for vacuum leaks, re-check timing, firing order, etc.

How does it idle? Put a vacuum gauge on it. Should read about 18-20inches and the needle should be rock steady.

 

check valvelash

 

check ignition too... take a crayon with the engine running and touch the exhaust headers one at a time.. I suspect you have a dead cylinder (the one that doesnt melt the crayon is the dead one)

 

Sounds like a cylinder isn't firing. Might want to do what pablo said and if that doesn't help, pull the plug wires and check that each wire is making spark. It's simple, get an extra spark plug, ground the threads to the chassis and have a friend turn the car over, the plug that doesn't fire means you've got a bad wire.

 

if its caused by crossed wires it will still spark

 

That's a no brainer. Definatly check to make sure correct firing order but what it sounds like to me isn't a crossed wire and is infact just a cylinder not firing. If it was a crossed wire it wouldn't even run as well as you're saying it does.