Cadillac Repair: cranks but will not start, fuel pump relay, cadillac deville

Question
91 cadillac deville with 4.9 engine.  Intermittent problem is driving me crazy.  99 times it starts right up, 100th try it cranks, engine turnsover but does not start.  Wait 5 minutes/several hours and it starts fine.  No driveability problems, no misses runs great.  Dealer had car for 2 days and it started evrytime for them.  They checked what they could but found everything fine.  No codes.  I've cleaned fuses, relays, pcm connections, and battery terminals.  Thought I may have beat it after I left battery disconnected for a time as I had no problems for several weeks, then it happened again.  I saw a similarpost dated 01/03/07 on a 93 Seville and have read about similar problems on other forums/boards so I'm thinking it might be fairly common but I can't find answers.  HELP!

Answer
Unfortunatley intermittents are very hard to find.

The next time it will not start check to see if it is getting spark to the spark plugs.

If it is, pour about 3 ounces of gas down into the throttle body where the air enters the engine and see if it trys to start, If it tries to start this would mean that you have a fuel problem that could be either a faulty fuel pump relay and or an intermittent faulty fuel pump.

Do you have more starting problems when the fuel tank is low on gas rather than when it is full of gas ?.