Hi all. I just pulled my 1986 F-250 460 down to the head gaskets and when putting it back together deleted all the smog equipment. It is still stock motor with stock holly carb with the exception I replaced the intake manifold. It all went well (with the great forum info). I went to start it up and it started and runs great for 1/2 minute and then runs out of fuel. I pulled the fuel line and it pumps when cranking but it must stop after letting the key go (run).

Has anyone run into this problem after deleting the smog stuff?

Everything seems to be hooked up right, it will start and run great every time I crank the starter and then runs out of gas. Float is good, I took that apart to check. I am getting oil pressure, gas gauge works, can switch between tanks with same result. I just seems like after letting the key go fuel pump stops.

Is there some way I can jump the start condition to see if it stays running?

appreciate any help. I am at the end of my rope.

Thanks, Mike.

 

If fuse 18 and your oil pressure switch are okay have you checked the inertia switch in the cab and the fuse link feeding it?

Investigate the fuel pump cutoff relay. -NOT the selector relay- because you are getting the system to prime while cranking.
Is there power to the relay on the yellow wire but the oil pressure switch is not pulling it closed?
​​​​​​​Is there no power getting *to* the relay?


​​​​​​​

 

You can see where yellow should be hot at all times.
Fuse link 'S' is connected before the ignition switch.

The oil pressure switch OTOH is only hot in start or run, through fuse 18

If you have power at the yellow lead to the relay you can try jumping the R/Y at Connector 343 behind the carburetor near the firewall to test the oil pressure switch.

 

The oil pressure switch for this system probably looks like a "emissions" device.

 

It's Tee'd off beneath the little tin can sender at the back of the block.

Subford has a good picture of it somewhere here on the forum.

Hard to imagine it as an emissions device, but he did say he stripped it down to the short block.
If it was removed, that would explain why the truck won't run.

 

Here's a pic of my aftermarket one:




And here's the factory illustration:

 

Thank you all for the replies.
I didn't remove the oil pressure sender even though you are right it does look like emission stuff. Everything electrical is still hooked up. I tried to bridge the plug under the oil sensor but didn't change anything. Like I said when it starts for the 1/2 minute I am getting good oil pressure. If I am understanding right by everything I have read on this forum, the fuel pumps only get a signal when it is cranking and then in run pos. Is there a separate signal from crank to run or is the same signal from crank just supposed to stay on after key is let go? For some reason when the key is let go it stops pumping fuel.

Thanks, Mike.

 

The oil pressure switch provides the power in Run - but obviously only when you have oil pressure.

 

No Gary, Look at the schematic.
Pink/black while cranking.
The yellow wire from the inertia safety switch in the cab provides power to the fuel pump relay, and the red/yellow from the oil pressure safety switch pulls that relay closed.

 

Ok, what I said was wrong, but what I meant was right. I should have said that the oil pressure switch provides power to the fuel pump cutoff relay in run. But, as Jim pointed out, the inertia switch provides the power to the pump itself. And, this diagram is easier for me to get my head around:

 

I didn't realize that the circuit had a resistance wire in it.

So what is the measured voltage at the fuel pump when truck is running (power coming through resistance wire?

 

If the inertia switch was tripped. The pump wouldn't pump even in cranking mode, no?
I can't measure anything while it is running since I can't run it long enough.
Am I correct in thinking that, if the oil sender is bridges then the fuel cut of relay should think it is in run mode?

Thanks, Mike.

 

Looking at the diagram it shows that when your cranking (start position) the inertia switch and relay are by-passed, so you would get power to pump while cranking. Then when you release the key to run position, the power switches to go through the inertia switch and fuel pump relay.

 

Can you ground the fuel pump relay wire in the EEC diagnostic connector and make the pump run continuously (for testing)?

Actually, I'm not sure if this ground at the diagnostic connector will work on a dual tank 7.5L (it does work on a 5.0L). Maybe someone can confirm.

 

No computer on this 460 so no connector like that.