Hi all, first posting here. I have a 1989 f150 4.9l 4wd with a fuel delivery problem. The fuel pump is not getting power. Fuel pump relay has been replaced. I can hear it clicking.

I checked voltage at the pump- nothing.

I fired up the pump with an external 12v source right at the pump itself and it works.

So there must be a broken connection or corroded wire between the fuel pump relay and the pump.

It appears the relay is trying to send about 6.8volts to the pump. this doesn't seem right to me.

I am in the process of getting some wire diagrams off Alldata at the library.

While I amuse myself with the info can anyone tell me what voltage the pump runs on? I would assume 12v, but when I performed a bypass of the circut and got the truck running fine the pump sure did seem loud from inside the truck.

Sorry for the long post and I probably left something out also.

 

Problem solved

 

So what was it, bad pump?

 

Inertia switch

 

I just went through the same exact thing on my buddie's 96 300 E4OD. Checked the fuel shutoff switch by the floor board passenger side and it was ok. Relay is ok too. So now he's running with a jumper wire to the pump and the pump did seem a bit louder but that could be my imagination. He's been having problems with turning the key in the ignition and I suspect the problem might be somewhere in the ignition. He has to play around with the key before it releases and turns to "ON" or "START". Other than that, I'm stumped. Wait, the fuel shutoff is the same as the inertia switch right? Man I'm stumped.

 

My fuel pump definitly ran louder when I bypassed the system. It must run on something less than 12v. It is not 6v cause I tried that in the bypass. I forgot to check the voltage at the pump after I got everything up and running ok.

The fuel shutoff switch is the inertia switch

Does your buddies truck have dual tanks? If so there might be something to check in that circut.

 

Single rear tank......Correct me if I'm wrong, but let's say you turn the key to "ON", I think your fuel pump will initially pressurize the lines for a couple seconds or so and if you don't crank the truck, it will shut-off....right? Maybe the PCM or EEC has a role in shutting off the fuel pump if the truck doesn't crank.

If this is true, then my problem could mean a faulty PCM. But, if the PCM is faulty, then wouldn't the truck run like crap? According to my buddy, it runs and feels the same as before. Now, my other buddy thinks there should be a fuse to the fuel pump but I don't know where it is. I checked all the fuses inside the truck and the ones by the relays and they're all good. He says current should flow from fuse--->relay---->shutoff switch----->pump.

Again, if the above is true whereas the pcm or eec shuts the pump off after it pressurizes the lines, then it may explain why the pump seems louder now. Now that I have the jumper on it, I can crouch behind the truck and really hear the pump good. Under normal circumstances, I can't move fast enough behind the truck to hear the pump before it is shut off automatically.

Don't know.... my truck is a 94 300-6 E4OD single rear tank as well. Maybe I'll bring out the ol' tester and trace the wires in my truck to see where they go. Maybe I'm missing something somewhere....

Come on, surely someone has had this problem.....help.

 

Fuel Control 1996 from PCM to Inertia Fuel Shutoff:

http://i54.photobucket.com/albums/g91/subford/Fuel/1996FuelPCM.gif

Fuel Control 1995 from Inertia Fuel Shutoff to single tank:
(Note, I can not find a 1996 single tank diagram. I can only find diagrams for two tanks. I think this one for a 1995 would be the same for the 1996.)

http://i54.photobucket.com/albums/g91/subford/Fuel/1995FuelPCMSingle.gif

 

You are right. Yes it does.Yes it would most of the time. He is right. Also the pump runs on 12 VDC (Battery Voltage). I do not like the term "pressurizes the lines". The PCM does not know if it did this or not, only that it let the pump run for one second. The jumper would not change the sound coming from the pump. The pump does not mind running all the time as the FPR just sends the fuel over 55 psi back to the tank. The reason the PCM turns off the pump is for safety reasons.

 

Now, my other buddy thinks there should be a fuse to the fuel pump but I don't know where it is. I checked all the fuses inside the truck and the ones by the relays and they're all good. He says current should flow from fuse--->relay---->shutoff switch----->pump.

Look for a fusible link just past the starter relay

 

On a 96 if the Fuse Links (two parallel 12 GA links) were open the truck would be totally dead with no power to anything (except the alternator B+ terminal).

Fuse #16 in the engine compartment fuse box, a 20A fuse, is the only fuse in the Fuel pump circuit.