Fuel Pump Problem

[93FordSc]

I have a 93 F150 4x4 with a 302, its got a single rear tank. I tried starting the truck and it just spun over and i didnt hear the fuel pump turning on. I replaced the Fuel pump relay, The inertia switch is not tripped, None of the fuses are blown. After checking all that i replaced the fuel pump earlier, after that i realized there is no power getting to the fuel pump. Anyone know what could cause this?

[losthillbilly73]

check the wireing at each point from the pump to the fuse if u dont have power anyware it could be the computer my buddy had a 95 that did the same thing

[93FordSc]

Is there anyway or anybody who can test the computer?

[losthillbilly73]

that i do not know hopfully some one else on here may be able to tell u. id just pull urs and go to a junk yard and get on from the same year engine and trans combo n swap it n see prefferably one with matching number but u can get them cheap in the junk yard.

and trans go under and see what trans u have

if u have over drive its either an aod or e4od

[93FordSc]

I just replaced the trans yesterday, its an aod But i dont even know if it works yet cause the truck wont start lol

[StrangeRanger]

Don't replace the computer till you have checked everything else.

Get a wiring diagram, a volt-ohm meter and work backwards from the pump
Is there power at the fuel pump?

Is there power at the output of the inertia switch?
Is there power at the input of the inertia switch

When you first turn the key on:
Is there power at the power out pin of the fuel pump relay?
Is there power at the power in pin of the fuel pump relay?
Is there power at the control pin of the fuel pump relay?
Is there a good ground at the fuel pump relay?

With the key on:
Is there power at the power out pin of the PCM relay?
Is there power at the power in pin of the PCM relay?
Is there power at the control pin of the fuel PCM relay?
Is there a good ground at the fuel PCM relay?

Is there power out at the fuse block?

The chances are that it's a wiring failure. Trace it, find it, fix it. Do not waste time and money buying parts you do not need until you have checked out the fuel pump circuit

[93FordSc]

StrangeRanger, i checked the pins of the fuel pump relay, only two of them are hot with the key on, But i do not know which pins are which.

[93FordSc]

The fuel pump relay clicks along with the ecm relay when i switch the key on.. then we tried grounding pin number 6 on the self test plug and the fuel pump relay clicks when grounded. But we still have no power to the fuel pump.

[StrangeRanger]

So you know that you have 12v at the fump relay input and at the relay control and that the relay cycles but is there 12v at the fuel pump relay output?
If not then it's a bad fuel pump relay
If there is 12v at the relay output but nothing at the inertia switch input then it's a loose or broken wire.
If there's 12v at the inertia switch input but nothing at the switch output it's a bad inertia switch
If there's 12v at the inertia switch output but nothing at the fuel pump, it's a loose or broken wire.
If there is 12v at the fuel pump but it doesn't run then it's a bad pump

[jethat]

wrong thread.

[93FordSc]

Does anybody know which pin on the fuel pump relay is the ground?

[StrangeRanger]

It doesn't have a ground.
The pin which would normally be wired as the ground goes to the PCM through what should be a LB/O striped wire. (I don't have a 93 truck wiring diagram)

[Steve83]

The wire that goes to the DLC is the "ground". Read this caption:



But you've already grounded it. Now with a ground jumper in the DLC & the key in RUN, check for 12V on BOTH inertia switch wires. Then check at the tank select switch jumper beside the headlight switch (that's most likely your problem). To access it, read this caption: