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baddiesel
03-31-2007, 14:14
my truck gets funny every 3-4 months start it up runs 30 seconds or so and stalls some times it starts right up and keeps doing it for like ten starts then runs fine other times it won't start just keeps cranking but then will be no problems for months. if it was the pmd would'nt it do it all the time? could it be the ignition switch i never remember to look at the gauges when it does it to see what they are doing. lift pump is working,checked all grounds all tight no corrosion. i have noticed quite a whosh upon fuel cap removal could that be it but again why does it only happen every 3-4 months. pmd was replaced at 88,000 by prior owner it now has 129,000 it is still on the pump.any one have any ideas where i should look
gmctd
03-31-2007, 18:25
Proper test for lift pump is engine idling, open the water drain valve - fuel should pour out, engine should continue to idle.

If engine stalls, lift pump is advertising, but you got no product - that is a solenoid-type pump, can buzz without pumping because the valves are leaky.
baddiesel
03-31-2007, 21:39
when it is running i have checked that plenty of fuel pours out no stall, but a lot of times when it goes on the stalling kick the lift pump runs a long time i've played around with it when it stalls left key off like almost 1 min and pump still running and think thats a little weird usually it stays on 5-10 sec after shut down
gmctd
03-31-2007, 22:40
Yep - should shut down soon as oil pressure drops.

Remove the Optic Sensor Filter - black rectabular rubber module, 6-wires - then connect the OS direct to the engine harness, try that.

Some '94-'95 needs the OSF, some don't - Bill Heath offers a replacement.

Could also be the LP is failing occasionally, or there is a leak between the tank and the LP, or the in-tank filter is plugged - could also be you need a new fuel cap, supposed to relieve at 1psi and 2" vacuum.

Most definitely move the PMD offa the Inj Pump B4 summer gets here, move it far away from the engine as possible, preferably outta the engine bay with 72" extension - and you'll need an appropriate heatsink