fuel system schematics
 

I have a 1988 GMC 6000 series truck (old Uhaul) With a 24 foot box on it. I am looking for a picture of the fuel system. It looks like it has a mechanical fuel pump on the engine and 2 fuel pumps in line. up by the front bumper. I don't understand why it would need all those fuel pumps. Anyone ever work on these bigger truck like this???? It is not moving any fuel/ I can see into an inline fuel filter and no Fuel in coming up.

gmc fuel Schematics
 

I am still looking for a schematic of the fuel system on a 1988 6000 GMC with a gas engine. It has multipal Fuel pumps on it. I think! One on the block and 2 electric up by the front fender. I don't understand why so many. It does have a step tank on the passenger side.