Only diesel I've ever owned before this was a 6.2 that never needed anything but oil changes..... So I'm lacking in diesel knowledge lol. It's a 95 C2500 suburban, 6.5 TD What I got going is a random starting issue that goes like this.... Key on, wait for GP light to go out, turn key and hold it..... No turny turny, but I get a sound like a normal electric fuel pump running (only while the key is being held in start position). If I hold the key that way for a while, some times it'll randomly start turning over after a few seconds. Most of the time all I get is that pump running sound. BUT!.... The odd part is that probably half the time I turn the key it starts just fine exactly as it should . My only theories so far are, 1. I'm losing fuel pressure somewhere while it sits (happens more often after sitting, but not always), and that pump sound is building it back up..... Would that prevent it from cranking though? 2. There's something wrong with the key/switch that's not cranking it. 3. Completely random thing that I have yet to understand because I'm dizzle dumb.