Electrical problem
1999 GMC Sierra V8 Four Wheel Drive Automatic 110000 miles
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Recently, When ever I try to start my truck at night, around 12:00am, the engine starts to turn over, the alternator kicks in but then immediately dies.

Any other subsequent attempts to start are no use until morning. Its definitely not a battery or alternator problem as those have already been checked out and are okay.

The thing that puzzles me, as well as the mechanics I've been too, is that this only happens at night. In the daytime, the truck gives absolutely no starting problems.

The mechanic hinted at faulty relays, I changed those but to no avail, the midnight problem persists. I think it may have something to do with daytime temperatures, around 80F vs 63F at night.

Not a big difference but could that be affecting something in the starting system? Another mechanic also hinted at a possible faulty fuel pump but wasn't sure about that one. Please help... Thanks in advance.