no power to lift pump

[oliver Ben]

I normally work on farm tractors, so tthis is new to me. Working on a 93 chev. one ton 4x4 with 6.5 turbo diesel. I don't have power to the lift pump. Checked for voltage with engine running. Can't find fuse on fuse block, was wondering where this was fed from, and what else is on this curcuit. If any one needs help with an oliver tractor, just let me know. Thanks Oliver ben

[JohnC]

There is an oil pressure switch on the rear of the driver's side head. Common problem.

[Robyn]

Fuse for the Pump is in the plastic junction box right behind the AC acumulator on the pass side.
Black little boxy thing held to the firewall by 3 plastic nut

The fuel pump fuse is on the far pass side of this box and the fuse holder plugs into a little holder.
Unplug the fuse assembly from the holder.

As John mentioned the oil pressure switch behind the drivers side head on the block.

Switch does two functions. 1 it sends the signal to the gauge and 2 it feeds power to the fuel pump once the engine starts.
There is also a realy in the junction box too.

The fuel pump receives power via that fuse and the relay from the start circuit and does so until the engine starts and the key is released.
Then the OPS closes and applies power to take over the job.

Check the fuse and possibly the relay.

You should have 12V to the pump with the starter in the crank position.

[oliver Ben]

It was the oil pressure switch. If this is a saftey device to save the engine incase of low oil pressure, I don't think it would work very well since the engine still runs without the lift pump working. It looks like it would would work if the oil pressure switch was wired in before the fuel stop solinoid on the injection pump to stop the engine because of no oil pressure. Well, no sense in reinventing the wheel. Thanks for your wealth of information Ben

[DmaxMaverick]

It was the oil pressure switch. If this is a saftey device to save the engine incase of low oil pressure, I don't think it would work very well since the engine still runs without the lift pump working. It looks like it would would work if the oil pressure switch was wired in before the fuel stop solinoid on the injection pump to stop the engine because of no oil pressure. Well, no sense in reinventing the wheel. Thanks for your wealth of information Ben

That's great you got'er figured out!

The OPS is a safety device, but isn't there to protect the engine. It is there to prevent the fuel pump from pumping when the engine isn't running, like after a crash. Mechanical pumps don't need this, because they don't pump unless the engine is turning. The IP will draw enough fuel to run the engine under low to medium power demand, depending on the IP health. If your engine runs with a failed lift pump, it indicates the IP is fairly healthy.

[oliver Ben]

sounds like the it's doing the same thing as a ford inertia switch. Thanks again for your help. If you all ever need assistance on oliver farm tractors just let me know. Thanks Ben

[Kennedy]

FYI, We've added the 6.5 coverage to our lift pump control harness eliminating the strain on the OE switch plus adding manual activation and a "prime" function at startup.