Sorry fuel pump again (complicated)
99 Suburban 5.7. Just bought this non-runner, but only 140K miles. Replaced
intake gaskets (big problemo), it's back together and realized that my FP isn't
priming (cycling) with key on. I have confirmed ECM B fuse is good, relay was
swapped with one from another running suburban (mine)- no change. Jumped
FP relay pins 87(B1) / 30(A3) which does activate the pump, sounds fine. So...
my pump, fuse, relay, and wiring to the pump all seem to be good, am I
dealing with some issue with ECM signal? Not sure where to go from here. I
can follow instructions but am not a whiz with a wiring schematic... (might try
another ECM tomorrow). Another possible clue is my volts gauge seems to be
dead with new batt, haven't noticed any other electrical equip that is inop at
the moment, don't see any "passlock"lights currently. . Thanks for any
assistance.
Note the diagram. The fuel pump relay has two sides, the switch side, left side in diagram, yes, if you pull relay, just terminals 30 and 87, the pump should run. Just because it runs, doesn't mean the fuel pump makes good pressure. need to check pressure, use a gage. The control side of relay, right side in diagram, needs voltage and ground to energize relay, you could, with relay unplugged, use both ends of test light on terminals 85 and 86, key or engine cranking, if lamp comes on you have voltage and ground good enough for test lamp. The control side gets voltage from vcm, the ground is chassis ground. also, in diagram, note the oil pressure switch, if voltage to switch and that switch is functional, when you crank it enough to bring up oil pressure and that switch closes, the pump should run, regardless of relay. That oil pressure switch is a redundant power supply to the fuel pump. Hope this helps, a little.
My bad, I looked at 98 silverado. that first line. 99 sub 5.7L, doesn't show oil pressure switch. voltage to control side of fuel pump relay comes from vcm.