A lot of the time, an extended crank condition can be narrowed down to one of the following:
1 - Fuel Pressure Regulator. Pull the vacuum line off of it. If it smells like gas or fuel dribbles out of the regulator OR the vacuum line, the FPR is bad.
2 - Fuel Injector. If a fuel injector is stuck open, it will leak down all the pressure into the cylinder. A massive backfire can occur if this is the case.
3 - Fuel Pump. There'* a check valve in the fuel pump to prevent fuel from leaking back into the tank. If the check valve sticks open, the fuel pressure will leak back into the tank.
Your best bet to narrow down the cause is to get a fuel pressure tester. Put it on the scraeder valve, start the car, shut it off and watch the needle. If it doesn't fall, it'* not a fuel delivery issue and more likely a VATS problem. If it does leak down, check the FPR. If that isn't leaking, pull the injectors and the rail (in one assembly -- don't seperate it! you don't need to, and it makes reassembly more difficult). Turn the key on to build fuel pressure and see if the injectors leak gas. If one of them does, you can either replace it or find a shop that offers a BG Fuel Injector Cleaning. Great product, I've used it at my shop for years. Takes care of the typical fuel injector problems found in GMs. If none of the injectors leak, you're looking at a fuel pump.
Any questions, lemme know. Good luck.
EDIT: Another way to determine if it'* a fuel injector leaking is if you have a misfire. The misfire is being caused by the excessive fuel leaking into the cylinder and fouling out the plug(*).
'94 Bonneville SLE | 266K miles
CAI - K&N cone filter - polished intake runners - 140 amp alternator - 2.5" exhaust - Magnaflow hi-flow cat - Magnaflow dual outlet muffler - 106K on engine and transmission - Sold 1/14/07
94 VW Jetta - 151K - 2.0 - 5 speed - Ghetto black steelie wheel mod - Techtonics 2.25" cat-back system