1986(1/2 year) f150 fuel system woes
10-01-2009, 10:34 PM
#1
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1986(1/2 year) f150 fuel system woes
Gah... And where to start.
Stats:
5.0L
MPFI
AOD
My truck has 3 pumps, one in each tank and one on the frame rail and none of them will turn on, I have bypassed the inerta switch(jumper wire), checked for power at the fuel pump relay and checked for power at the tank changeover switch, I'm not sure which pins need continuity on the switch but my ohm meter shows that both sides are good and now I'm lost as a ***** in church.
I did check to see if I could feel the relay cycle when the key is turned.
One strange thing, when I check for power to the changer over switch plug, my test light comes on then fades off for a "second" and keeps doing so in cycles, not sure if that's normal.
One last bit of info, when I switch tanks my fuel gauge always reads empty(this is a new symptom) and I know both tanks are atleast 1/4 full.
Stats:
5.0L
MPFI
AOD
My truck has 3 pumps, one in each tank and one on the frame rail and none of them will turn on, I have bypassed the inerta switch(jumper wire), checked for power at the fuel pump relay and checked for power at the tank changeover switch, I'm not sure which pins need continuity on the switch but my ohm meter shows that both sides are good and now I'm lost as a ***** in church.
I did check to see if I could feel the relay cycle when the key is turned.
One strange thing, when I check for power to the changer over switch plug, my test light comes on then fades off for a "second" and keeps doing so in cycles, not sure if that's normal.
One last bit of info, when I switch tanks my fuel gauge always reads empty(this is a new symptom) and I know both tanks are atleast 1/4 full.
10-02-2009, 01:08 AM
#2
Senior Member
Here is a diagram:
http://i608.photobucket.com/albums/t...FIfuel-sel.gif
The change switch is really 2 switches. One side changes the tank pumps and the other side changes the tank senders. The gauge wire does pulse on and off every few seconds if I remember it is 5 Volts.
Note that the fuel gauge and tank pumps will not function when the selector switch is pulled out of the connector.
The fuel pumps / relay will only be energized for about 3-5 seconds each time the key is turned to the on position. If engine does not start then the pumps are turned off until the key is switched off and on again.
You can force the pumps to stay on by putting a jumper on the test connector somewhere. Don't know the details of how to do that. You could jump the pk/bk wire with 12V and see if the high pressure pump comes on, then work back from there.
Very hard to tell if the tank pumps are working unless you disconnect fuel lines at the selector reservoir and see if they pump fuel out when the key is turned.
http://i608.photobucket.com/albums/t...ordfuelres.jpg
Recently replaced the rear tank including sender and pump. I also replaced the troublesome tank selector/ reservoir / filter thing with an electric tank switcher.
Also look at this thread for some detailed testing instructions:
https://www.f150forum.com/showthread...cks#post214811
http://i608.photobucket.com/albums/t...FIfuel-sel.gif
The change switch is really 2 switches. One side changes the tank pumps and the other side changes the tank senders. The gauge wire does pulse on and off every few seconds if I remember it is 5 Volts.
Note that the fuel gauge and tank pumps will not function when the selector switch is pulled out of the connector.
The fuel pumps / relay will only be energized for about 3-5 seconds each time the key is turned to the on position. If engine does not start then the pumps are turned off until the key is switched off and on again.
You can force the pumps to stay on by putting a jumper on the test connector somewhere. Don't know the details of how to do that. You could jump the pk/bk wire with 12V and see if the high pressure pump comes on, then work back from there.
Very hard to tell if the tank pumps are working unless you disconnect fuel lines at the selector reservoir and see if they pump fuel out when the key is turned.
http://i608.photobucket.com/albums/t...ordfuelres.jpg
Recently replaced the rear tank including sender and pump. I also replaced the troublesome tank selector/ reservoir / filter thing with an electric tank switcher.
Also look at this thread for some detailed testing instructions:
https://www.f150forum.com/showthread...cks#post214811
10-02-2009, 06:10 AM
#3
Senior Member
Diagram that klricks put up shows the EEC relay has to be powered up to provide the closing action of fuel pump relay. Also show an additional fuseable link there.