Just had another thought, cool 2 thoughts in 1 night aaahhh the mind enhancing power of beer
Anyway so you dont have 12 volts on the power (red) wire at the connector to the pump. The pump connector is hooked up and there is 12 volts on the power wire without the pump connector on the pump.
To me this means that the voltage is all being dropped prior to the pump motor, corroded connector on the power wire or possibly a very burnt contactor on the power relay.
So try bypassing the relay with a jumper wire. Figure out which wire has the 12volts into the relay and which one has the 12volts out to the pump and simply jump these 2 wires together. If the pump runs the relay is bad. If it doesn't run the problem is somewhere between the relay connector and the pump connector.

Sparky

 

Thanks Sparky, I will try it tommorrow. so the power goes from the power distribution box to the relay on the fender to the Inertia Switch to the fuel pump. Is that correct?

 

I would think that is the correct route for power flow, that being said I have never owned a truck with an electric fuel pump. Way to new for me I do however love working on a good electrical problem, some people say I am sick LOL

Sparky

 

I also seem to recall reading a Tsb dealing with a wire splice on the fuel pump relay circuit that can work loose ....All I recall is that the splice can make intermittant or completely lose contact breaking the circuit to the relay .

 

Ok..... so now I am getting frustrated. I THINK I located the fuel pump relay. Is it located in the Power Distribution Box under the hood? I think it's there because in the owners manual it says Relay - Fuel Pump (see graphic below)

So I started all over today and hooked the volt meter up to the connector at the fuel pump again 12 volts. Connected the fuel to the connector and checked the voltage at the pump and got 0 volts, disconnected the pump and got 12 volts again. Connected the fuel pump directly to the battery and it works fine.

I then connected the volt meter back to the connector at the pump and started pulling relays in the Power Distribution Box, the voltage never dropped even when I pulled the one that says it is for the fuel pump.

What next???? Any Ideas???? HEEEELLLLPPPPP!!!!


http://www.atlanticjetsports.com/temp_stuff/f150pdb.jpg

 

Inching evvver so close. Well, I jumped the positive battery lead at the fuel pump relay to the lead that goes from the relay to the Inertia Switch and then onto the fuel pump and the fuel pump turned on immediatly! So you would think it was the relay right..... wrong. I bought a new relay and as soon as I plug it in the voltage drops to 0. So the line from the relay to the pump seems to be all in tact and working properly. What next???

 

Well process of elimination dictates the problem is in the power wire to the relay or possibly the relay socket itself.
I sure wish I has a wiring diagram, or maybe the truck to look at
Is it possible to jump the power in to the relay to the power out from the relay? Pump should work this way, if it doesn't the problem is in the power feed to the relay or the relay socket itself.
Does the power in to the relay come direct from the battery thru a fuse? Or is there other "gismos" in the way like computers and such??
Possibly a corroded fuse? Or fuse socket?
Keep up the troubleshooting, it is getting close to being solved.

Sparky

 

Hey Sparky,
Listening to the advice of a mechanic (and against my better judgement) we went and bought a fuel pump. There goes $160.00 down the drain, same deal.

At the relay there are four wires. One is hot power feed from the battery through a 20amp fuse. Directly across from it is the lead that goes to the Inertia Switch and then onto the pump. The other two leads have power to them when the key is switched "ON".

I jumped the hot lead across the the lead going to the Inertia Switch and then onto the pump and the pump starts right up. When I plugged the new relay in I get 0 volts at the pump.

Am I right in assuming that the line from the relay to the pump is fine because the pump fires right up when you jump power to the lead at the relay?

With the relay plugged in you can feel a slight click on the relay when you switch the ket to "ON" but again at the same instance the voltage to the pump goes to 0. If I do not connect the pump but use a test light or volt meter every thing is fine when you switch the ket to "ON".

http://www.atlanticjetsports.com/temp_stuff/f150dg.jpg

 

This may seem silly but have you tried starting the truck. It seem to me if the system has a relay in it it is due to the fact that the pump needs to be able to shut off. It could be that the system is presurized and shut the pump off so that it will not burn up. If it was a constant pump you would not need the relay at all.

The system is not calling for fuel so the computer tell the pump to shutdown. Once it gets a call for fuel it will turn on the pump. While the engin is running the pump need to supply the high pressure pump will fuel. Have you verified pressure at the fuel rail. It may be up to pressure and just shut the pump down.

I just went through a similar issue as I could always hear my pump prior to top end rebuild of my 351w. Now I can nolonger hear the pump at key on but it is working properly....

Mark

 

I tried cranking the motor over for about 15 seconds but the pump never kicks on.

 

Does the schematic I posted above give any indication what to check next?

 

ajs,
lets look at this for review.

Direct connect to bat works.
You have power to the fuse box Key on
You have power to the relay Key on
You have power to the pump connector Not on Pump

Once you connect the pump the power drops to 0.

does this summarize the situation so that We are on the same page.

Mark

 

Ya Mark that is what is going on.

If I attach the pump and jump power to the wire going to the pump starting at the relay it works also.

 

Really sounds like a short! The fuse never blew, but the relay is opening. I think I would start at the relay and work my way back to the bat and then back to the pump. But it really sounds that the pump is causing a short in the system.this could be due to a wire chaff. When you disconnect it from the pump is is separated from the frame and when you connect it to the pump it again makes contact with the frame or something else.

I would really check the wires because it may have just been opened when he last drove the truck...

Best bet...

Mark

 

I have to disagree. Since he jumped the relay and the pump worked and no fuse blew a short is ruled out. The question is why the voltage is dropping to zero when the relay is used.
When you use a jumper you are simulating the relay contacts are closed, and the pump runs. This means, the pump, its power wire, the ground, the fuse and power supply are operating correctly. It has something to do with the power relay being opened.
I have looked at the schematic and there is some info missing. the relay shown on the left top corner, what is it and what closes it? This relay controls the 12volts to the close coil of the fuel pump relay. Also the ground for the fuel pump relay coil isnt shown, although it shows the circuit going to the EEC. This maybe a dumb question, but what the heck is an EEC? Remember I own old trucks read pre-EFI, apparently for a good reason I can usually diagnose their electrical problems quicker
You can try putting a ground to the "To EEC" pin of the Fuel pump relay. If the pump relay closes and the pump runs it is a ground problem. If it doesnt work, try 12 volts to the "From EEC" pin of the fuel pump relay if it works it is a power problem. Of course I have no idea what effect this may have on an EEC, in theory it shouldn't have any ill effects. But theory and practice are different.
I will try and check back later today, but I have the work thing on the go now.

Sparky

ps
too bad about the new fuel pump you bought..... a little bad advice I guess