Hey Frank2008FRD make sure you have a operational low pressure pump in the tank you are drawing off of as even though the high pressure pump in frame deliver's high pressure, does not pull well. Will exsperiance stalling, surging, and no restart till cool especialy in hot weather.

 

Darn , that means I'll have to lower the tank again , but it should be easier the second time around. I may try to salvage the low pressure pump from the rear tank that I removed.
The truck has sat for so long that the midship fuel pump looked like some thing from the Titantic!

 

Goodness, you guys have provided tons of info! 1986 F150 302 EFI. Fuse was not installed when I acquired the truck, and being a 302 gasoline would explain that I now see. I've got a 6 line selector and noticed the replacements are quite a bit smaller. I've suspected a possible rupture in the diaphragm but it works fine on the front tank. I haven't gotten under the truck with a multimeter yet but intend to check if that rear pump is even getting power. The other thing I've considered is just flip-flopping the supply/returns on the selector valve which would be a lot more free to test for a ruptured diagram, in theory...

As of late, I've lost the inclination to crawl under the truck after finding a nice bundle of dog chewed wires and the plastic protective covers... Yes, my dog so she's still alive...

 

sckirklan
That selector valve is not electrical and has no wires going to it, it switches off the running in-tank pump.

Here is how it is wired if you need a diagram.


Selector Valve:

 

That's exactly what I was looking for! Thanks!

Is this the kind of goodies found in full fledged shop manuals?

 

No, The photo I took and the diagram I drew on my computer.

Here are some more photos.
Fuel Selector Valve:


Low Pressure Fuel Pump plug:


Low Pressure Pump:


Inertia Switch:


Fuel Pump Relay:

 

Bill K,

I'm just checking impedance on the fuel sending unit yes?

Thanks!

 

I am not sure what you are asking.
The sending unit is for the gauge and you could check the resistance to ground at the selector switch. When the fuel is low the resistance is high and when the fuel is high the resistance is low.

As for the pump with the fuel pump wire disconnected (unplugged) at the selector switch you should have complete circuit to ground (truck body) through the pump and the resistance should be about the same for both pumps.



The truck battery is disconnected for the above tests.


If this checks out listen at each tank for the pumps (when selected) to run for the one second after the key is turned on with the engine not running and the battery hooked back up.


Note that the hi-pressure pump on the frame will run for the one second with either pump selected.

 

@Bill,

Sorry for the lack of clarity and that was just what I was after.

Thanks!

 

Well, I finally got to jacking with the truck this weekend and find myself with more questions.

First of which being, is the grey, 6 connection connector that clips onto the fuel selector switch a replaceable item from ford still? There's tiny clips that hold in the connectors which one broke but I can press it from behind after it's plugged in to make connection.

Also, I checked resistance at the switch and it was good so I pulled the cluster and checked the wire from the fuel sending unit and got connection, however I didn't bother to check to see if it was same or close as it was at the selector switch. I just went ahead and plugged the main cable back to the instrument cluster and the fuel gauge moved slightly so I'm wondering if this means I've got a gauge issue and how to test (volt stuff that actualy passes or if it's all ohms), flooded float, or a screwed up fuel level sending unit.

Also, I noticed that unhooking power to the high press. pump made it terribly easier to check the tank pumps even so considering the back pump doesn't work and I get no resistance from the sending unit, but that's a later battle. I'd be nice if it was just a bad connection that needed reseated, also I've been eyeballing those huge rear tanks drop down to spare tire height roughly. I just fancy $140 at the pump!

footnote, thanks a ton for the pointers Bill K. Those color codes for the sending unit made my life much easier. I was considering dropping the tank and testing that way! Now I just need to get this darn gear selector cable out so I can take the instrument cluster off all the way. That one has me wooped for now.

 

Are you talking about the plastic clip or the metal clip?

I do not think you need to pull the cluster, the gauge wiring is at the selector switch also. The gauge itself is seldom the problem.
You will have to test in ohms as the voltage is of pulse type from a voltage regulator on the cluster.

Just push in a little and squeeze the tabs and pull it off.

 

it's a grey plastic, 6 pin connector that plugs directly to the back of the tank selector switch. It's not terribly crucial as I can just push the wire in that isn't locked into the grey plastic clip.

what I was hoping to do is manually force the gauge to move between max/min ranges and didn't know if there was a minimum voltage I could use to do so with.

I'm trying to remember what the connector looked like on this short cable but it seems a though it had an obtuse triangular thing I could push on but I sure didn't want to break it not knowing what to do!


Also, after having had taken all this crud apart and reconnecting the instrument cluster the fuel gauge moved slightly where it had not moved at all before, so in my infinite wisdom I topped off the tank... I'm not a big fan of dropping a tank full of fuel, rather trying to put back a tank full of fuel. Are there any references you know of that might have spec'ed out the min/max values for the sending unit's resistance?

The company I work for also takes care of the local ford dealer's network and computer equipment and I take good care of them. I'll have to see if they have shop manuals for this dinosaur they might part with or lend me.

 

I don't know if I forgot to mention but that wiring diagram came in handy, thanks again Bill!

 

To test the gauge just unplug the connector at the selector switch and turn on the key switch, the gauge will pig in one direction then short the gauge wire (yellow wire with a white stripe) in the plug to ground and it should peg at the other end of the scale.
If it does this it is OK, if not well......

 

that connector is a pain to get to and it'd be easier for me to just stick a test prong on the wire from behind. do you think that should do just the same? seems to me shorting it is shorting it.

Thanks!