Fuel pump question

I have read back several years of post and can’t seem to find the answer. First vehicle description.

1986 Ranger 4x4 ext cab 2.9l automatic

My in-tank fuel pump continues to run. It doesn’t shut off after the normal 2 seconds for prime other symptoms is fuel gauge doesn’t work and no power uphills or high speed. My guess is that the pump is going or gone bad. Any ideas that I should consider before I start chasing this problem down?

Welcome to TRS

1986 will have 2 fuel pumps
Low pressure lift pump in the tank
High Pressure pump, for fuel injection, in the frame rail under drivers seat area

1987 and up just had 1 high pressure pump in the tank, so late 1986 could have just 1 pump

In either there will be a Fuel Pump Relay, it will have a Green Base and be located on the inner fender in engine bay
The computer runs this relay, by Grounding it

When you turn on the key, the computer and this relay gets 12v, computer then Grounds relay for 2 seconds on startup, then unGrounds it.
If Relay is staying closed, fuel pump stays running, then Ground wire is bad(shorted to ground), could be computer issue but usually not.
If relay was bad, stuck closed, fuel pump would run even after key was turned off.

Previous owner may have shorted this relay's Ground wire, so fuel pump comes on with the key on.
You need to find the OBD 1 connector in the engine bay to see if that was done.
Look here: http://therangerstation.com/tech_library/OBD_I.shtml

There is a drawing of the OBD connector in above link, it is usually located on main wiring harness by firewall passenger side.
Fuel Pump Slot is IDed in drawing
That is the Ground for the Fuel Pump Relay, if that slot is Grounded with a jumper wire then Relay will close when key is turned on.
Check if the previous owner did that

Lack of power or stalling out at higher speeds could mean the high pressure pump is failing, OR fuel filter is dirty.
It could also mean low voltage going to fuel pump.

In the passenger side of cab in foot well there will be an Inertia Switch, look just above carpet under glove box.
The inertia switch has a metal weight inside and Red Button on the top, if there is a sudden stop, accident/rollover, this weight will move and cut power to fuel pumps(s), safety feature.
You can test voltage going to the fuel pump at this switch.
Test battery voltage first, should be 12.3-12.8volts key on engine off
Test voltage at inertia switch, should be exactly the same voltage
If it is less than 10v then there is a dirty corroded connection between battery and inertia switch so fuel pumps can't output maximum pressure.

Power path
Battery-----------Fuel Pump Fuse----------Fuel pump relay---------inertia switch-------------Fuel Pumps

In 1986 the fuel pump fuse will most likely be a Fusible Link, these are short wires that will separate, like a fuse, if there is a short, they are used for alternators and other higher amp circuits in place of inline fuses.
They are connected to Starter Relay, battery post side, then spliced to regular wire going to the device, in this case the Fuel pump relay.
The Splice can get corroded over time reducing voltage.


MAP(Manifold pressure) sensor, 1986 will use speed density system(computer) with MAP sensor
MAP sensor should be on firewall, it has 1 vacuum line and a wire connector
It reads the vacuum level in the intake manifold and computer bases Fuel Mix on that level, so very important sensor, like MAF sensor on newer models.
Find MAP sensor, check its vacuum line, needs to be air tight, check wiring connector, unplug it and make sure connections are clean and dry

RonD said:

Welcome to TRS

1986 will have 2 fuel pumps
Low pressure lift pump in the tank
High Pressure pump, for fuel injection, in the frame rail under drivers seat area

1987 and up just had 1 high pressure pump in the tank, so late 1986 could have just 1 pump.

Click to expand...

The 2-pump system continued through '87 and '88, there's no chance that a fuel-injected '86 had only 1 pump.