Fuel pump issues

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Jul 10, 2006 | 12:29 PM

mpahl

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Fuel pump issues

I have a 1990 f150 302 with two tanks... Lo and behold I go to start it this morning and nothing. I can't hear the fuel pump start to whine, so I start trying to trace down the problem... Here's where I'm at:

At the pump I have 4 wires, Black, Black with yellow, Red, and Orange. Red has 6 volts, I assume that must be for the gage, black and black/yellow seem to be grounds, orange has nothing...

At the relay, my yellow is hot (as it should be)... To test the relay, I decide to jump it to the brown (that was what I understood the relay to do) and it starts smoking and popping... Bad idea...

I'm no expert at these trucks, but know my way throught the diesels inside and out... This is my first gasser and I'm getting a bit frustrated...

Why did jumping the relay cause a groundout? What wire at the pump is supposed to be hot with 12 volts?

I'm tearing my hair out...

Jul 10, 2006 | 01:04 PM

jimbob21rc

Senior User

Joined: Feb 2005

Posts: 432

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From: Pulaski, TN

check all your fuses, i had a similar problem with mine and i was 100 miles from home, finally got it hauled home took off the bed, checked all the wires, and finally found a bad fuse and it wasn't even to the fuel pump but after i replaced it it worked fine, it was the fuse to the daytime driving lights and i don't have day lights, so just replace all bad fuses, that can never hurt!

Jul 10, 2006 | 01:23 PM

d_stange

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Joined: Jan 2006

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From: Bertha Minnesota

If you have dual tanks check your tank selector switch. Take it out and see if it half melted like mine was. I checked a lot of stuff and that was my problem. Also check you interia switch.

Jul 10, 2006 | 04:22 PM

subford

Fleet Owner

Joined: Aug 2005

Posts: 23,666

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From: Easton,Ks

Here is a diagram:

Last edited by subford; Jul 10, 2006 at 04:28 PM.

Jul 10, 2006 | 04:41 PM

subford

Fleet Owner

Joined: Aug 2005

Posts: 23,666

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From: Easton,Ks

Quote:

Originally Posted by mpahl

At the pump I have 4 wires, Black, Black with yellow, Red, and Orange. Red has 6 volts, I assume that must be for the gage, black and black/yellow seem to be grounds, orange has nothing...

Front Tank
Black = Ground Gauge
Orange = Ground Pump
Red = Hot (+12V) Pump
Dark Blue with Yellow = Gauge to Dash

Rear Tank
Black = Ground Gauge
Orange = Ground Pump
Brown with White = Hot (+12V) Pump
Yellow with Lite Blue = Gauge to Dash

Gasoline Engine
Voltage is supplied to the Fuel Tank Selector Switch whenever the Fuel Pump relay is energized (contacts closed).

When the Fuel Tank Selector Switch is placed in the FRONT position, power is supplied from the 786 (R) terminal of the Switch to the Front Tank Fuel Pump Motor. Fuel is pumped from the front tank. The signal from the Front Tank Fuel Gauge Sender is carried through the 673 (DB/Y) wire to the Fuel Tank Selector Switch, and then through the 29(Y/W) wire to the Fuel Gauge in the Instrument Cluster.

When the Fuel Tank Selector Switch is in the REAR position, power is supplied to the Rear Tank Fuel Pump Motor through the 789 (BR/W) wire from the Fuel Tank Selector Switch. The Rear Tank Fuel Gauge Sender signal is transmitted to the Switch through the 675 (Y/LB) wire, and then to the Instrument Cluster through the 29 (Y/W) wire.

Sound like you may have a bad front pump or a short in the wiring or switchs.

Last edited by subford; Jul 10, 2006 at 04:58 PM.

Jul 10, 2006 | 05:38 PM

mpahl

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Ok... Thanks for the diagram and info... I tried grounding pin 6 on the EEC and that too just grounded out, so I must have a bad ground fault somewhere in the tank selector switch, the fuel pump, or the wiring in between... Anyone have any other ideas?

Jul 10, 2006 | 10:32 PM

tim73

Mountain Pass

Joined: Feb 2003

Posts: 136

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Id check my F/P relay first. Pull it out, and put 12V to the coil pins, you should hear the coil pull in. If you dont then it is probably bad. But you can pull the relay out of the horn and try it also, if it(The horn relay) is working. Then I would check your inertia switch. If it has 12v on it, when the relay is pulled in, I would suspect my selector switch. If you have a meter, just trace out the wires, youll find the problem.