1996 Cadillac Deville Cold start problem

Describe the condition when it won't start. Is it an extended crank, accompanied with a rough run and possibly some smoke from the tailpipe? Is it a Northstar or 4.9L? A couple of things to check would include a leaking fuel pressure regulator, there would be fuel in the vacuum line, and for consumption of coolant with no external sign. Another check would be fuel pressure at cold start, does it prime in 2 seconds, and is it adequate(45 psi)?

I would lean towards the regulator, pull the vacuum line from the regulator itself, and check for liquid(raw) fuel. The other causes for extended crank would be fuel pressure, and possibly a missing cam sensor signal. The latter could bring a check engine light, but not necessarily.