1987 - "Another no power to the fuel pump"

[cal74]

I know this is a repeat and I've read several of the posts, but I'm lost.

1987 Ranger 2.9 (manual if that matters)

Replaced the fuel pump (2x) now

Replaced the fuel relay (2x) now

12v at the Relay

Inertia switch is bypassed, but I'm only ready a trace of voltage at that point.

Grounds off battery are connected, could probably be stripped and re-done but really not all that bad.

Not sure what to try since I'm not getting voltage at the Inertia switch, or what was the inertia switch?

This is (was) my run around/hunting truck, but it's getting close to being sent to the crusher if I can't get this figured out.

Thanks for any help.


ps: Can't recall the color of wires coming to the inertia switch, but which is the hot one coming in or which is supposed to be?

 

[RonD]

Dark green/yellow stripe wire at inertia switch comes from Fuel Pump relay.
Pink/black stripe wire on inertia switch goes to the fuel pumps

Fuel pump power runs like this:

Battery-------Fuel Pump Fuse(30amp)------Fuel pump relay----------inertia switch-----fuel pumps(1987 has 2)

If you pull out the Fuel Pump relay from its Green Base, make sure key is OFF
Use volt meter or test light to check each slot in the base.
Ground the volt meter or test light, then test each slot.

Only 1 slot will have 12volts, that the 12volts from the Fuel Pump Fuse
If no 12volts then fuse is blown, 1987 could use a Fusible link instead of fuse.
Fusible link would run from Battery post on starter relay(solenoid) directly to the Green Fuel Pump relay base.
A fusible link is like an inline fuse, it is a small gauge wire that will separate if too many amps are used.

If you have 12volts on 1 slot, then turn the key ON
Test slots again, there should now be a 2nd slot with 12volts, that 12volts is from the EEC relay(Brown base), next to the Fuel Pump relay.
This 12volts comes from a Red wire on the EEC relay.

The computer Grounds the Fuel Pump relay to send power to the inertia switch and then fuel pumps.

To test that you will need to find your OBD1 test connector, should be near firewall in engine bay, passenger side or drivers side, look for the main, largest, wiring harness and it is usually hanging off of that.
Look here: http://www.therangerstation.com/tech_library/OBD_I.shtml

2nd drawing down shows what you are looking for.
In that drawing one slot is labelled Fuel Pump
That slot is the Ground for the Fuel Pump Relay
It is spliced to computer's wire that Grounds the Relay.
So if key is ON, and you use a jumper wire to Ground that slot, you should hear the fuel pump Relay "Click" closed.
If that works then pull off the jumper and cycle the key OFF and then ON again, you should hear the Fuel Pump relay click Closed and then click open after 2 seconds.
The computer only Grounds the Fuel pump relay for 2 seconds when key is first turned on, it won't Ground it again until engine is running, RPMs above 400.
If cycling key OFF and ON doesn't Close the Fuel Pump relay then wire at the computer or the computer itself is bad.

Put jumper back in place and Fuel Pump Relay should be "Closed" you can now test for 12volts at inertia switch.
And the wire going back to the fuel pumps.

The high pressure pump in the frame rail is spliced into the original wire that runs back to the intank low pressure fuel pump, that splice can fail, so follow the wire from the high pressure pump to where the splice is and check it.

 

[cal74]

Thanks for the reply Ron, raining here and getting dark fast but will poke around a bit.

 

[cal74]

OK - I've got 6-7 volts to the inertia switch when I cycle the key.

I've grounded the fuel pump to the battery with the key on and I can here the fuel relay click.



I tried jumping the inertia switch to the fuse panel also.


Not getting anything?

Wire broke, I'm presuming?


What about wiring in a new relay directly to the pump?

 

[RonD]

The 5 to 7 volts at the inertia switch with key on is "monitor voltage" from the computer.
It has no amps so won't turn on the fuel pump.

You should see 12volts at inertia switch for 2 seconds just after key is turned on or all the time if you have the Ground jumper on the OBD connector hooked up.

But lets try something else
Pull out the fuel pump relay, leave key off
Test which slot in the green base has 12volts(thats fuel pump power)
Mark that slot or for sure remember which slot it is.

Turn on the key
Now check each slot for the 6-7volts, coming back from inertia switch
If you can't find it then that wire is bad
Double check that you do have 6-7volts at inertia switch, with key on
If so, but no volts at relay base then run a new wire from relay base to inertia switch
You may want to get a new relay base, the connectors inside may be worn out

If you do see the 6-7 volts at a slot in relay base then put in a jumper wire between 12volt slot and the 6-7volt slot
You should now have 12volts at inertia switch and fuel pumps should be on
If pumps are not on then wire from inertia switch to pump is bad

 

[cal74]

Thanks again, I will try it as soon as it quits raining.