Thanks for the tip. Never thought about measuring 12V from inertia switch. Yes, I remember fuel pump gets 12V only for a few seconds @key on engine off. I will run this test tomorrow and report back.

The switch was not tripped. I gave it a push-down just to make sure.

Thanks for the horn power explanation. Horn not working seems to be an unrelated problem. I will investigate it and post questions in another thread.

Oh, by the way, I checked all 3 square relays, PCM, HORN, and FUEL PUMP. All checked out ok. Applied 9V between 85 and 86, and got continuity between 87 and 30.

 

At the inertia switch connector (removed from inertia switch), DK GRN/YEL gets 12V a second and drops to 6.7 V.
With the connector plugged back into inertia switch, PINK/BLK gets 11+ volts a second and drops to zero.

Also, disconnected pump connector and checked harness side (sockets). 2 thick wires (RED and BLACK. +12V drops to 6.7 V in a second).
Also, checked ohm resistance at the pump connector (pins). 2 pump wires less than 1 ohm. 2 sensor wires 150 ohms.

Do you recommend at this point pump replacement? Any additional test? Thanks.

PS. Symptoms: no start, zero fuel pressure, no fuel pump humming sound

 

don't mean to but in butt you need to do this test with the engine cranking to properly load the circuit. I can not see the whole thread for some reason so ignore me if you have done this koec and sometimes voltage does not tell the whole story either.

 

Sorry for my ignorance. Please kindly explain to me what to do during koec. Thanks.

 

That's nonsense. It is NOT necessary to perform the test while cranking. If the pump motor won't start when the engine isn't being cranked when battery voltage is minimally loaded, it will also fail during cranking.


Yes, that's what it looks like.

 

Thanks. Just ordered a pump and a strainer. Since the fuel tank is full to the neck, I will have to wait until the fuel is siphoned off to my other cars. I will report back upon completion of the repair. Thank you.

 

hope the fuel pump gets you back on the road. the reason you should do a voltage test during cranking is because your looking at voltage alone no current nothing and its not uncommon for the voltage test to pass key on engine off and not turn the pump on than it is during cranking in other words properly loading the system can reveal low power issues that were not present with the key in the on position.


not to complicate things because 90 percent of the time with no fuel psi and good voltage its almost always a bad pump.

 

Thank you carguy94 for the explanation.

Gas tank is full. I need to drain it, at least half empty before dropping it. I read in other threads about antisiphon blockage. If this is true, I need to remove bed (reg cab long bed). I am without helper. I am thinking about lifting up the bed from under with floor jack. Will it work? Thank you.

EDIT: I found a youtube video on bed tipping (on GM pickup). Remove bed bolts on the driver side. Leave bed bolts half-engaged on the passenger side so that the bed doesn't slide off and fall. Lift the driver side a foot and prop with 2x4. Gas tank on this GM vehicle is at the same location as F150. Has anyone tried this?

EDIT: Disregard above request. I found multiple threads about disconnecting rubber section of the fill line from the tank and placing a siphoning line into the tank. Thanks.