Hey folks, first post here. Just picked up this 1997 f350 7.5 460 big block 2wd, stick, drw...picked it up last week. I bought this truck for my welding business (one man shop) and it came with a nice welding bed and a good condition sa-200 welder. Had to tow the thing home due to a bad brake line that completely disabled the brakes. Well I fixed the brake lines and replaced rotors,calipers etc. and after getting it all back together the truck wont start.
It started fine and ran strong before, but for some reason something electrical happened while i was working on the front axle.

Here is my symptoms: ignition on equals fuel pump running nonstop, and just wont start. I read in another thread on this board that the computer or something wont allow the truck to start with the fuel pump running.

So my goal is to try and get the fuel pump to stop. Here is what I did so far:
1. removed each relay in the fuse box separately and see if it kills the fuel pump. None stopped the fuel pump with ignition on.
2. Try to locate the pcm and remove harness plug to see if that shuts fuel pump off. Well I'm having a hard time finding the pcm because this truck was converted to run dual fuel cng and I was told the tank ended up failing and the cng conversion being abandoned.

Does this photo show the oem pcm replaced with this dual fuel pcm? or is the oem pcm still somewhere where I don't know where to find it?


I have 3 separate wire harness plugs that attached to this aluminum dual fuel box and I removed all three and the fuel pump still runs with the ignition on.

Not sure where to go from here. Need this truck running asap for my work. Thanks for any help anyone can give. -Tyler.

 

And that would be the brake booster bottom right of photo.

 

Most of the wires that go to those three harness plugs gets routed up and around the fuse box and right to this location here:


A couple other things I'm trying to factor into the equation:



And with this wire removed from the fuse location the fuel pump stops. But still wont start. If I take the 25amp fuse located on the wire and plug it into the fuse box spot where the wire is plugged in the fuel pump shuts off, but still wont start. Not sure what to think. And here is the truck:

 

that switch with the red and yellow wires going to is is most likely for switching between cng and gasoline.

 

+1 on this. Put it to the gas selection and give it a try.

 

Ya the switch has not been touched so it should be in the correct position (even though the position it is in is "gaseous" so im thinking they just wired it wrong and said the hell with it.) regardless i tried starting the thing with it in both positions and no go.

​​​​​​​Question: would having this fuel pumprunning longer than it should cause the engine to become flooded?

 

No, that means the computer is bad. Very common failure mode....continuous running fuel pump when turning the key from Off to Run.

The computer in question, PCM in Ford terms, is located under the brake booster.

 

Can someone please post a photo of where their pcm is installed? Im at a loss. I dont see any aluminum type box under the brake booster. The only thing i see, which is somewhat under the brake booster is the aluminum dual fuel circuit board box that i have in one of the pictures above.
A search reveals on pcm's that are sold online for this truck that there is only one wireing harness going to it. That dual fuel thing that is pictured looks as though there is factory oem wiring going to it in three different wiring harnesses.

Idk

 

Perhaps I should rephrase...the PCM connector is located under the brake booster as shown in your previous photo. The PCM itself is located behind the driver side kick panel/park brake support. It is removed from the engine side of the fire wall.

Perhaps a view with the fenders removed would help.

courtesy of Subford

 

Ahh. Okay. its the single big plug that has a 10mm or so bolt that you have to remove in order to remove the wire harness?

Well if thats it. I just removed that today and then attempted to turn the key on and I still get a constant fuel pump noise.

In other threads I searched here, one of the posters mentioned that if you remove the harness from the pcm and the fuel pump stops then that means your pcm is at fault.
In my case, the fuel pump didn't stop.
I removed all the relays in the fuse box and still didn't get the fuel pump to stop.

 

Sounds like you've got a real mess on your hands, unfortunately. They likely just ran a wire straight from a switched ignition source right to the fuel pump circuit.

First step will be trying to see if you can pull any codes from the truck.

 

Sorry for the confusion on my part..if this were a stock truck the constant running fuel pump is a sign of a bad computer. I completely overlooked the photo you posted stating if you removed the added fuse the fuel pump(s) stopped.

I do not see where spark was checked?