87 F150 Won’t Start

[Mhfco6]

Alright in this picture, the following leads are hot when dash switch is on Tank B. The inertia switch and the rear tank pump. (Pink w/ Black Stripe and Brown w/ White Stripe)

When I switch to Tank A the following leads are hot. Tank A Pump (Red).

Should there be any other leads hot during between Tank A/B and what should they be? It appears the sending unit and the pump ground are shared. Where is exactly do they meet and ground... on the frame?

 

[RonD]

Yes, that reads correctly

Pink is always 12v with key on and FP relay jumper in place, and you should HEAR the high pressure pump in the frame rail running

In B Brown wire should also be 12v, and Red wire 0v
In A Brown wire 0v and Red wire 12v

The sender(yellow/white wire) uses 5v but pulsed 5v so may or may not show up on volt meter
But you can use a OHM Meter to test the in tank senders
1987 probably uses the "old" Ford OHMs
73 ohms EMPTY
10 ohms FULL
If you rock the truck so gasoline sloshes you should see the float going up and down by the changing OHMs

So KEY OFF, test the yellow/green and blue/yellow wire OHMs to ground

 

[Mhfco6]

Yes, that reads correctly

Pink is always 12v with key on and FP relay jumper in place, and you should HEAR the high pressure pump in the frame rail running

In B Brown wire should also be 12v, and Red wire 0v
In A Brown wire 0v and Red wire 12v

The sender(yellow/white wire) uses 5v but pulsed 5v so may or may not show up on volt meter
But you can use a OHM Meter to test the in tank senders
1987 probably uses the "old" Ford OHMs
73 ohms EMPTY
10 ohms FULL
If you rock the truck so gasoline sloshes you should see the float going up and down by the changing OHMs

So KEY OFF, test the yellow/green and blue/yellow wire OHMs to ground

I haven't done the jumper yet. Does it need to go from the single STI port to the fuel pump port on Diagnostic? Right now the High Pressure fuel pump and Tank B pump run as long as the key is on. I was only using a test light to check for power in the switch. When I got the meter reading for the tank pumps, I used a fuse for power side and put the ground side on the tank switch. Hope I'm doing this right. All your help is appreciated, I'm trying to eliminate buying expensive pumps if I can get them working. And no sense in buying pumps if the issues is something else.

 

[RonD]

That's odd, one of the safety features on Ford fuel injection computers was only a 2 second run of fuel pump with key on, so if in an accident and fuel line broke engine would stall, and 0rpms = fuel pump off, so fuel pumps wouldn't feed a fire

So no need for the jumper, but computer may have an issue, maybe bad capacitors, they leak after 20+ years, easy to fix

So you don't hear the fuel pump in tank A when switched?
And does the red wire have voltage with switch in A?

 

[Mhfco6]

That's odd, one of the safety features on Ford fuel injection computers was only a 2 second run of fuel pump with key on, so if in an accident and fuel line broke engine would stall, and 0rpms = fuel pump off, so fuel pumps wouldn't feed a fire

So no need for the jumper, but computer may have an issue, maybe bad capacitors, they leak after 20+ years, easy to fix

So you don't hear the fuel pump in tank A when switched?
And does the red wire have voltage with switch in A?

I have never heard the pump in Tank A, ever.
Yes the Red wire has voltage when switched to A, no other wires have voltage.
I may get a wild hair and drop the tank to see wth is going on.

 

[RonD]

No other wires have voltage?

So pink wire loses voltage in A position?
Thats wrong

Pink wire should have 12v regardless of switch position, thats the IN from inertia switch

 

[Mhfco6]

Voltage readings are as follows when switched
from Tank A and Tank B.

TankA
Yellow/light blue - 0.00
Yellow/white - 8.49
Dark blue/yellow - 8.47
Pink/black - 12.30
Red - 12.26

TankB
Red - 0.04
Brown/white - 11.98
Pink/black - 12.29
Yellow/white - 1.98
Yellow/light blue - 1.95

 

[Mhfco6]

While trying to hook up STI my green Fuel pump relay just quit on me. HP pump stopped working and no juice to the dash switch. I can jump the relay and everything works again.

 

[RonD]

Forget the 2 yellow and the blue wires they are for the sender(fuel level), no connection to pumps

Just pink, red and brown wires are for the pumps

TankB
Red - 0.04
Brown/white - 11.98
Pink/black - 12.29
This is correct and pump was ON, notice the voltage drop between pink and brown

TankA
Pink/black - 12.30
Red - 12.26
Brown/white ?? but should be 0 volts, like red was above
So this is correct as far as the switch goes but no voltage drop so pump was not running in Tank A

Whats an STI, code reader?

Yes, if computer is working FP relay should NOT be closed(working) so no power at A/B switch or HP Pump with key on

And jumper would get it working again, key on only
Not sure why it was on full time in the first place

Previous owner may have slipped in a Ground on the back side of that OBD slot, because of a previous issue, and you moving it around pulled it loose
Or the ground wires on that slot have a bare spot that is grounding out to fender or firewall causing FP Relay to come on full time???

 

[Mhfco6]

Forget the 2 yellow and the blue wires they are for the sender(fuel level), no connection to pumps

Just pink, red and brown wires are for the pumps

TankB
Red - 0.04
Brown/white - 11.98
Pink/black - 12.29
This is correct and pump was ON, notice the voltage drop between pink and brown

TankA
Pink/black - 12.30
Red - 12.26
Brown/white ?? but should be 0 volts, like red was above
So this is correct as far as the switch goes but no voltage drop so pump was not running in Tank A

Whats an STI, code reader?

Yes, if computer is working FP relay should NOT be closed(working) so no power at A/B switch or HP Pump with key on

And jumper would get it working again, key on only
Not sure why it was on full time in the first place

Previous owner may have slipped in a Ground on the back side of that OBD slot, because of a previous issue, and you moving it around pulled it loose
Or the ground wires on that slot have a bare spot that is grounding out to fender or firewall causing FP Relay to come on full time???

The jumper will get it working like it was before. If I turn the key on now, nothing happens and there is no voltage at the dash switch. Maybe relay is bad, either way I need a new one.
So rear pump is running, but no pressure.. needs to be replaced. Front pump is not running, needs to be replaced. Safe to say the pumps are shot? What about the frame rail High Pressure pump? STI I’m referring to is the diagnostic ports.

 

[RonD]

Did you disconnect Pump B's line from canister and see if if it has flow when powered on with switch?

If you haven't been inside the tanks before pump be may be OK but lift line to top of tank is just rusted/rotted out, or its sock filter is clogged up
If pump is running it should be pumping, these turbine style pumps, do quit working, electrically, but usually don't quit pumping, but of course anything is possible, lol

 

[Mhfco6]

Did you disconnect Pump B's line from canister and see if if it has flow when powered on with switch?

If you haven't been inside the tanks before pump be may be OK but lift line to top of tank is just rusted/rotted out, or its sock filter is clogged up
If pump is running it should be pumping, these turbine style pumps, do quit working, electrically, but usually don't quit pumping, but of course anything is possible, lol

Yes for laughs I added 2 gallons of gas to the rear tank and got a small trickle of fuel, I said okay.. hooked the selector valve in the frame back up and turned the key. Fuel pressure was 10psi and truck would not start.

 

[RonD]

So HP pump was working
Reads like sock filter in tank B is clogged up

But odd engine didn't start, 10psi should be enough for start and idle, I wouldn't hit the freeways though, lol

 

[Mhfco6]

So HP pump was working
Reads like sock filter in tank B is clogged up

But odd engine didn't start, 10psi should be enough for start and idle, I wouldn't hit the freeways though, lol

What’s wierd is it WAS working last time I worked on the truck. This time it started and slowly started to die, I watched fuel pressure drop at the same time.

 

[RonD]

Yes, the canister may have gotten enough fuel in for some reserve, and you were running on that, so that would confirm HP pump is working