No power to inertia switch on 01 ST

[Bill in Denver]

I didn't find the specific answer so I thought I throw it out. 2001 Sport Trac, relays tested, voltage to pin 30 of FP relay and PCM relay, fuses ohm good, but there is no voltage on the grn/wht wire at the inertia switch. I did hot wire 12v to the pink/blk to energize the pump directly and the 15a fused wire I used to hotwire it immediately popped the fuse. So while the pump may be bad (or a short between the inertia switch and pump) that doesn't explain no power at the lead side of the inertia switch when everything back upstream checks ok.
Ideas?

thanks

Bill

 

[Josh P]

Do you have power on pin 86 of the FP relay? without a trigger, it won't energize the circuit.

 

[Bill in Denver]

Do you have power on pin 86 of the FP relay? without a trigger, it won't energize the circuit.

did not check 86, just 30. Will check 86 tomorrow - thanks

 

[Josh P]

did not check 86, just 30. Will check 86 tomorrow - thanks

86 is hot with the ignition on, it is the power from the pcm

 

[410Fortune]

And the fuel pump only primes for a few seconds unless the engine is running, so power will only be there for a second during prime
The pcm turns the fuel pump relay on and off

Simple enough to bypass (jumper) the inertia switch for testing
inertia switch is easy to test continuity with the red button pressed, no continuity with it tripped

 

[Bill in Denver]

And the fuel pump only primes for a few seconds unless the engine is running, so power will only be there for a second during prime
The pcm turns the fuel pump relay on and off

Simple enough to bypass (jumper) the inertia switch for testing
inertia switch is easy to test continuity with the red button pressed, no continuity with it tripped

inertia switch I don't think s the problem as there is no power down at the switch. But that was one of the first things I did yesterday was to jumper the pins on the switch plug. When that didn't work I checked for power there and there was none. Working backwards "uphill" now.

 

[Bill in Denver]

voltage check - The relay that is noted as fuel pump is 50B (5 pin relay labeled 1-5). PCM is noted as 54 (5 pin relay noted as 30, 85, 86, etc). I have constant 12v on 30 and switched 12v on 86 (never goes away) and on pin 1 on 50B is similar 12v switched. So I have no triggered short term (2 second prime) voltage on fuel pump relay.

 

[Bill in Denver]

update. Like an idiot, I didn't try to start the Trac after checking the relay yesterday. Guess what...it started...briefly. Ran for about 10-15 seconds then died. Restarted but idled roughly then died, restarted/died. No restart since. I can hear what sounds like the pump cycling (the 2 second prime). So thoughts? I'll put a fuel pressure gauge on it this afternoon if I have time to see if anything is happening when it cycles, but right now it sounds like it might have been a dirty contact or its still a bad relay. For $8 I'm going to replace it anyway. And possibly a fuel pressure regulator...
thanks all for your help so far
Bill

 

[Josh P]

When was the last time the fuel filter was changed?

 

[Bill in Denver]

When was the last time the fuel filter was changed?

I bought it as a non-runner so if I do have to drop the tank for the pump it'll get replaced anyway. At this point, its a "down the road" thing if I can figure out the fuel pressure thing

 

[Josh P]

I bought it as a non-runner so if I do have to drop the tank for the pump it'll get replaced anyway. At this point, its a "down the road" thing if I can figure out the fuel pressure thing

A non runner purchase is good information. There is a good possibility the fuel pump is getting weak.

 

[Bill in Denver]

A non runner purchase is good information. There is a good possibility the fuel pump is getting weak.

well, it wasn't until messing with the relays that I even had power down there...so one step at a time

 

[Bill in Denver]

we have liftoff!

Interesting tho - swapping the relays around did nothing. On a whim, I bought a new relay and plugged that into the fuel pump relay socket. Started right up. Post start, I had a bad miss. Someone had miss-wired the coil pack swapping 5 and 6. Runs like a champ now.

Thanks all for your assist

Bill