Trying to perform a compression test on a 92 f250 with the 351. Haynes manual says to disable the fuel circuit. Need to know how to do this. Thanks!

 

Welcome to the site..

Couple ways you can cancel the pump,,

Out in the engine compartment fuse box you can just remove the fuel pump relay, or, remove the EEC/computer relay (it supplies power to the fuel pump relay) or remove the fuse/s for either power distribution for these relays. Don't remember the positions, but there 20amp/yellow fuses 'hot at all times'.. There's also a gray color EEC power diode there, if that's removed it will kill power to the EEC power relay..

Can't remember,, but i think the relay position is noted on the underside of the box lid. Last, you can unplug the connector on the inertia switch located in the right/upper kick panel..

 

I used what I thought was a simple way to disable the fuel pump.
With the engine running give that inertia switch a sharp rap with your hand and you will hear it trip and almost immediately the engine will stop running due to the lack of fuel .
The fuel pump is now prevented from working. When done with whatever you are doing reset the switch and you're ready to go. I believe your inertia switch for F series should be located at the center of the dash on the transmission hump or near the steering column.

 

Thanks guys I appreciate it. I just pulled the fuse and it was good to go. The cylinders tested at around 100-125 psi. They started at around 30 and worked there way up with each crank. I know this means the rings are most likely bad. The truck is more of a beater and I wanted to make sure that it didn't have any compression problems