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  #1  
Old December 21st, 2006, 06:10 PM
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Exclamation Fuel System Electrics

Ive been working on a fuel pump issue for some time now and was wondering if any of you had any knowledge on the subject.
The end result is that my fuel pump wont turn on. There is no power at the pump, but even when I try to put 12 volts directly on the connectors on the top of the tank I dont get the pump to run. ( does anyone know which prongs are for the pump and which are for the fuel gauge?)
All of this is after I had the pump out and checked it, and put it back in the tank, hooked it up, but didnt put the tank back in the truck, and it worked then too.

Now, ive gotten my voltmeter out and noticed that there is 12 volts between #30 and #87 on the relay recepticle in the passenger seat box, but only .1 volts between #30 and #87A. Is this whats supposed to happen? Is there any way to check if the relay is good? Anything else I should be checking here?
I dont know if this is a result of the above, but I only get 6 volts at the fuse. I dont know of a good way to check at the inertia switch without tearing it apart, but the switch is not triggered and there is no voltage at the tank.

Does anyone know what went wrong? All i did was snip the 2 ground wires at the tank and ground them to the frame and spliced in a wire off of the pumps power wire to have an easy check in the future.

Thanks in advance.
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  #2  
Old December 21st, 2006, 07:04 PM
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Tried to Im you while you were on but missed you I think. Do you have the wiring skematic or are you going solely by the relays under the passenger seat.

Also I am a little confused as to what you did with the ground wires from the tank. From your explanation it looks as though you tied the grounds to a spot on the frame???? and a power wire??????

I don't know if it is already posted somewhere but I could send you the wiring skematic of this circuit so you can see where the power is supposed to be. You should have power on the White/purple wire on 87 of the fuel pump relay for 3 seconds when the ignition is turned on. Then it stops until the engine is turning over or running. You have to check it in that window or it isn't on. Also if you are checking the inertia switch you could simply see if you have 12v in and 12v out.

I dont mean to oversimplify some of this but I have been there confused about WTF was going on. Hopefully this helps. Otherwise PM me and Ill try to get you the information you need

Tim
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Old December 21st, 2006, 07:14 PM
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Tim,
I spliced into the existing ground wires(both the pump and level gauge ground) and drilled a hole and put a screw in to ground the wires more securely.
I also spliced into the white and purple power wire and just have a length of wire that I can check to see if there is power.

I have the wireing diagrams from the shop manual.
Thanks for the help
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Old December 22nd, 2006, 12:51 AM
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I don't know, maybe run a jumper wire from the fuel pump relay to the pump itself by-passing the inertia switch and the harness to the pump. If the pump is grounded and there is power there it should run.

Keep us up on your progress
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Old December 22nd, 2006, 09:42 AM
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I have read someplace that the connections at the tank sometimes come loose. Not the plug itself but the wires going into the plug on the harness side.
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  #6  
Old December 22nd, 2006, 11:59 AM
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Thanks for the info guys.

Im still concerned with the fact that there is only 6 volts at the fuse box. Does anyone know whether the 87A terminal should have 12 volts running through it?

Also, is there a way to check if the relay works? I think it is fine, but I would like to know for sure.
Thanks again
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Old December 22nd, 2006, 02:42 PM
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Yes there is a way to check if the relay works. If there is power to pin 30 and pin 86(both should have 12v), and the ECM is grounding pin 85 then power should go through the relay to both pins 87 and 87a both receiving 12 volts.

Which fuse do you only have 6volts at?
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  #8  
Old December 22nd, 2006, 08:45 PM
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ok. a very long story told short... i wasnt checking for voltage within the 3 seconds at the pump ( i know, im a little slow). THe end result is that after banging the tank around with a rubber mallet, it runs great.
I have no idea why.... but thats what happened. I was doing something stupid with the voltages, but I still dont know how to check if the relay works. How can you tell if 87 and 87a have 12 volts if you have to have the relay connected? just run some wires between the connections i guess?
Anyways, after a lot of hassle, all it took was a good knock on the tank and its running fine. Well see how long that lasts...
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