I have a 1990 7.3l that has been causing issues here recently. It was running well until it just shut off one day. Went to start it and it fired right up, but when I let go of the key it shut off. I found that If I hold the key It will stay running, but when it returns it dies. I have replaced the ignition cylinder in the column and the ignition box down on the steering column with the same results as above. Any ideas of what to check?

 

Update:

Took the ignition switch and tripped it by hand with the same result. Looking for a wiring diagram.

 

It sounds to me like you are losing power to the Fuel Shutoff Solenoid when the key is in the On position. It takes 12V power to open the FSS so fuel can pass through the injector pump. There is a wire connected to the FSS inside the pump- disconnect it. Disconnect the engine starter relay so that the starter won't receive power. Connect a voltmeter to the FSS wire and see if you have power when the key is in the Start position and also in the On position.

 

Where is the Fuel shut off solenoid located?

 

As I said earlier "inside the pump".

 

Only have power with the key in the start position. No power when in run to the FSS. Is there anything that stands out why this would be or will it be a wiring problem?

Thanks for your help so far!

 

Every Ford with the key switch in the steering column that I've worked on has a metal rod that runs from the key down to a box at the base of the column. When you turn the key the rod pulls/pushes a set of sliding electrical contacts inside the box. A wiring harness plugs into the side of the box. For some reason (maybe a burnt contact) your FSS wire is not receiving power in the Run position. The easiest thing to do would be to replace the box but if you buy one and it doesn't fix it then you've wasted money. Maybe a junk yard would let you test a used one on your truck.

 

I replaced that ignition switch already with no changes. The only possibility (If it's that)would be a faulty box.

 

You may need to re-align the ignition box.

 

As short term fix, you can run a jumper hot wire from your battery to the FSS on the IP. That will let you drive, but you have to open the hood each time to start and shut off. But better than being stranded with no vehicle.

You definitely need to trace back the wiring and figure out why no +12v in the on position.

 

DO NOT TRY TO REMOVE IP TOP COVER! Do the glow plugs click when you turn on the key to "Wait to start" ? ....There is 2 fuseable links





This has the FSS wiring should help ya out....Check the big plug it might be dirty.

 

update. Have no power off of the glow plug relay where the FSS wire goes. The Glow plug relay does have constant power plus the purple wire (WTS light wire) has power.

Is this relay bad?

 

Quite possible from the sounds of it. I would say something isnt right with that there relay....thats my guess and im not good with engine electrical. The other post should have a wire on it(dont remember the color) That should have power when the key turns on, if its not there, run a jumper wire from the post from the battery to the other side, it should turn on and you will hear a click from the contacts closing(Dont quote me here this is what my 83 did)

 

Got it taken care of. Found some bad connections coming from the right side and cleaned up most of the wiring while I was there.


Thanks for everyone's help!

 

What exactly did you find by any chance? I'm having the exact same issue with the same truck.