btfarm - being a Vortec there's no magnetic pickup coil in the distributor like the TBI units, and yeah those are somewhat known for going bad. The Vortec setup though just has a reluctor type wheel and the cam sensor, hall-effect style setup, and the cam sensors rarely go bad.
6.2 turbo - excellent advice on the distributor gear as the Vortecs are known for having a batch of improperly heat treated gears that went horribly bad, way prematurely. Apple core wear is the common failure and they will run like crap.
You don't just set the timing to zero with a timing light on a Vortec though, unfortunately. They had to go and make it a pain. There's no bypass wire to disconnect like on a TBI setup.
Best thing to do is not attempt adjusting the distributor unless you have a scan tool on hand that can read the "cam retard" figure, and usually it takes a somewhat high end scanner, though several of the lower end Auto Xray units are capable. If pulling the distributor, make TWO marks - the distributor body position AND the rotor position. When reinstalling, attempt to get it as close as humanly possible to those same two marks. That should allow it to run well enough to fine-tune with the scanner. Then use the scanner and adjust the distributor until you get the cam retard number to within +/- 2 degrees from zero - while holding RPM's to at least 1,000 to ensure a good reading. You cannot do this based on the reading at idle or below 1,000.
Now while I believe the distributor gear is high on the suspect list, you should also check the distributor itself for wear in the top bushing. Grasp the rotor and try moving it from side to side. If it doesn't move, gently twist it either direction to see if it turns, then try the side to side movement again. If you can get any real noticeable movement...time for a new distributor.
While we're at it, I know the FPR and spider have been replaced (hopefully took the opportunity to ditch the poppet valve setup and go for the MFI conversion with the individual injectors) - but what's the fuel pressure looking like? If it's not 58~62 psi then you still have a fuel delivery issue. Vortec small blocks do not like it at all when fuel pressure falls anywhere short of spec, especially with the poppet style injector setup, it really requires fuel pressure be up to spec to force those valves open.
Richard
