Fuse 34 keeps blowing and we determined that this is the injector circuit. I dropped the fuel tank and want to test the fuel pump. I don't know how to test it, I figured I could do an ohms test. Does anybody know how to test the fuel pump and what the ohms should be on which leads?

2004 - F150
5.4L Triton
4x4
automatic

Thanks in advance.

 

Are you sure it's not the FPDM?

Attached are the fuel pump pin outs.

 

I am not sure of anything, but my fuel pump does not have 6 pins, only 4.

 

Pin 2 (or 4?) in the plug diagram he attached is "PUMP MOTOR".

But given common FPDM problems, I would suggest checking the plug 'toward' it for short to ground as @ManualF150 suggested.

 

That is an incomplete description. F34 feeds 1) all 8 injectors, 2) the PCM, and 3) the fuel pump via the FPDM.

To isolate, start removing loads from the circuit and see when the fuse stops blowing (key in RUN). You can, if you wish, go with a static measurement with the battery disconnected and an ohmmeter between F34's load terminal and ground measuring in the lowest scale. It would take a resistance of under 2 ohms to blow a 20A fuse so you'd be looking for a "good" reading of more than 2 ohms.

1. Trip the inertia switch or remove the fuel pump relay. If the fuse still blows, it isn't the FPDM or the fuel pump.
2. Remove connector C175b. If the fuse still blows, it isn't the PCM.
3. Injectors are harder since there's no single connector to unplug so you'll have to unplug each of them individually. If the fuse still blows, you have a wiring harness issue where a wire is chafed or pinched and is shorting to ground.

Good luck.

 

Thanks so much for the detail. I will work on this over the next day or 2 and report back.

MK

 

So there are no codes in the system, and I am fairly sure there is a short to ground somewhere. I am going to let a professional deal with it. Thanks for the advice guys.

 

No problem. Good luck.

Come back to us when the pro figures it out.

 

If you're going to pay them anything, don't give them @projectSHO89 's post.

 

Turned out to be the FPDM. The case was cracked in half.

 

Ha. Knew it.

At least you got it fixed.

 

^^^^^^^ gets 5 gold stars '*****'