My son's 1995 Blazer has a fuel system problem that I just can't kill. I have replaced the fuel pump, fuel filter, ECM, checked all ground & continuity of complete fuel system. I have sufficient fuel pressure at the schrater valve. With new pump & filter it starts, but only when tank is over half full. When its low on fuel, we pour fuel directly in the upper intake and it will start and continue to run. It just won't start and run on its own. We were thinking that there is a valve at the tank on the return line that may be stuck open, and when the system has enough fuel to start, it will stay running. After shutting it off for awile (overnight) the fuel will drain through the return line open valve into the tank, then it doesn't have sufficient pressure to start. This is a guess. Also when we replaced the pump the sock was completely coated, so we air-hosed it fairly clean. Maybe this is a problem too. We are very frustrated, and I'm sure my 17 year old son won't keep it full all of the time. Any thoughts on why it has starting problems with less than half a tank? Thanks to everyone, as I have learned a lot from this forum to this point.

 

*Moving to 2nd Gen Tech*

What happens if you cycle the key a few times to prime the fuel system (ie. turn the key to run until the fuel pump shuts off, back to off, then run again until the fuel pump shuts off, then to start)?

Its possible that the new pump has a defective check valve in the fuel supply line. The return line is unrestricted from the FPR to the tank. The check valve in the fuel pump assembly and the FPR hold pressure in the fuel supply line. The only thing that I can think that would be fuel level dependant would be a problem with the fuel pump assembly.