GM-GMC: Stalling, oil pressure switch, engine oil pressure

Question
I have a 1996 Silverado 4x4 with a 6.5 diesel,the last 3 days it just quits while i am driving along, it always restarts some times I make it home with out problems up to 20k other times I drive 20 feet and it quits again but i am able to restart and usually make it home. The last time it quit I could not hear the fuel pump running but when I turned the key off and back on again the pump started up .I have had different amounts of fuel each time from 1/8 to 3/4 tank .I have replaced the fuel filter and drained the line and bled air from the filter. I suspect some type of electrical problem.

Answer
Your problem is likely with the Oil Pressure Switch (OPS).

GM designed these engines with electric fuel transfer (lift) pumps and needed to ensure that the fuel supply was shut-off in the event of low engine oil pressure or an accident.

The trouble is that the lift pump draws about four Amps and the OPS is rated for about one Amp.  Over time, the OPS contacts go bad and this causes the lift pump to shut off and starve the injection pump for fuel.

From diesel forums (my diesels have electric lift pumps but no OPS), I believe that the test is to open the fuel filter bleed valve with the engine idling.  If fuel does not flow out in a solid stream, then either the OPS or electric lift pump is bad.  You can run +12 Volts to the pump directly and retest.  If the fuel flows properly, the OPS is bad.

The OPS is located on the back of the engine, near the driver's side cylinder head.  I understand that a special socket is recommended for removal and replacement of the OPS.