Most likely you are loosing fuel or ignition. When it wont start you need to check for spark. If you have spark check to confirm that the fuel pumps are running. This is a starting point on the tree of diagnosis. There are many branches to follow. Once you eliminate one of these two possibilities we can preceed from there.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k