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'93 F150 dual tanks not working

 
Old 08-30-2011, 02:48 PM
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Originally Posted by bluecar5556
The fuel tank selector switch is (2) DPDT switches linked together, one DPDT switches the fuel gauge sending unit and the other switches the fuel pumps, as illustrated above. Just because the fuel gauge switch from one rheostat to the other, does not mean the other fuel pump switch isn't worn or faulty that terminate at the fuel pumps. Makes sense, those contacts have to switch a several amp payload (fuel pump) vs. a very small current passing through a rheostat and energizing the windings inside the fuel gauge to move a very light armature.

This is why I am stressing to test the voltage at the fuel pump before replacing it. The fuel tank selector switch could have a bad contact, here.
And of course you are correct. I had a brain fart.
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Old 08-30-2011, 03:34 PM
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Originally Posted by bluecar5556
The fuel tank selector switch is (2) DPDT switches linked together, one DPDT switches the fuel gauge sending unit and the other switches the fuel pumps, as illustrated above. Just because the fuel gauge switch from one rheostat to the other, does not mean the other fuel pump switch isn't worn or faulty that terminate at the fuel pumps. Makes sense, those contacts have to switch a several amp payload (fuel pump) vs. a very small current passing through a rheostat and energizing the windings inside the fuel gauge to move a very light armature.

This is why I am stressing to test the voltage at the fuel pump before replacing it. The fuel tank selector switch could have a bad contact, here.
That's exactly what I said...with less words...and not quite as technical..
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Old 08-30-2011, 03:42 PM
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So I did the turn the key on with the rear tank selected and heard the fuel pump "priming" and when I have the front tank selected I didn't hear the fuel pump "priming"
So, I guess I will check the fuel pump relay and the voltage at the pump and if that is all good I will drop the tank and replace the fuel pump. Sound Good?
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Old 08-30-2011, 03:54 PM
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Flip the fuel tank selector switch to "front."

No point testing the fuel pump relay as it is supplying current to the rear fuel pump adequately but what you can do, is remove it and using a jumper wire, bridge pins 30 to 87. This will mimic the fuel pump relay being ON as if the engine is running. This is so you do not have to keep turning the ignition switch on & off, only getting 2 seconds of power, now you will be getting power constantly.



Using a multimeter on Volts DC, back probe the fuel pump connector.
Orange=GND
Red=12V
and you should be getting 12.6V or battery voltage.


Last edited by bluecar5556; 08-30-2011 at 04:04 PM.
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Old 08-30-2011, 06:10 PM
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Last edited by bluecar5556; 08-30-2011 at 06:39 PM.
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Old 08-30-2011, 11:38 PM
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Or you can jumper the data plug to ground to kick the relay on.


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Old 08-31-2011, 03:17 AM
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You are correct, pin#6 on SPOUT connector is 86 (EEC GND signal) on the fuel pump relay socket.

Easier procedure and FP relay is tested at the same time, good to know. Thank you, Nitehawkjr

Last edited by bluecar5556; 08-31-2011 at 03:23 AM.
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Old 09-26-2011, 11:38 AM
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Fuel Pump was bad...I replaced it and she is running like a dream. Thanks for all your help!
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Old 01-22-2019, 11:41 PM
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not one of you “experts” find a problem with bluecar5556 ? “Use oxy/act torch to cut access hole”
This is the advice the moderators find acceptable? And I don’t see one member question him either.
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Old 01-23-2019, 10:51 AM
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Get over it - it was EIGHT YEARS AGO. And it's a public forum; not a professional council. Your post isn't helpful, either. Do you expect the moderators to ban you for it? They don't police the technical content - they only enforce the user agreement. Have you read it?
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