GM-GMC: 1984 6.2L Diesel 1/2 t pickup, psi air, gasoline engines

Question
I have a 1984 6.2L chev diesel 1/2T pickup, worked great until 3 weeks ago...we did an oil change..everything appeared fine...started the truck, it ran for about 5 mins and quit....hasnt run since...we suspected the starter was the problem, as, we had 2 new batteries in it and they were drained and very low after letting the truck sit for 3 days....my husband removed and checked the starter...it was shot, he rebuilt it ( very good mechanic, but, is NOT overly familiar with diesels....), the truck starts now but wont run...no fuel is getting to the motor.....we cannot remember how to purge the fuel lines ( and we were told NEVER let a diesel run out of fuel )...have you any suggestions, advice, or instructions , in particular about purging the lines, and in general, about what else could have gone wrong.( we feel that the alternator is ok..)...
This truck has been a dream to operate in all the years we have had it....
thank you, in advance, for your help....any at all would be much appreciated...
Norma

Answer
Norma,

I agree about the 6.2s being good engines...I have enjoyed both of mine.

The problem you face is that the engine has a mechanical lift pump (for fuel transfer) and this pump is nearly exactly the same as those used on carbureted (gasoline) engines.  In a carb, fuel sits in the bowl and is available when the engine is cranked.  Not so with a 6.2 diesel.

The easiest way to purge air from the low pressure side of the fuel system is to use 3 to 5 psi air and pressurize the fuel tank at the filler neck, using a rag to form a seal.  Open the bleeder valve on the top of the fuel filter and listen for air to bleed out.  This will be followed by fuel after the air is purged.  If no air comes out, temporarily bypass the lift pump at its location on the passenger front of the block.  Once the fuel filter is full of fuel at the bleeder, the bypass can be removed.

Next, disconnect the two wire connector at the glow plug relay (usually next to the start battery on the driver's side fender).  There is no need to use the glow plugs at this point.

After purging the air out of the low pressure system, loosen all of the injector lines at each injector and crank the engine, in short bursts with time to let the starter cool down, until fuel drips out of each injector line.  There won't be much fuel, just small drips.  As each injector line drips, it can be tightened on its injector.  After more than half the injector lines are tightened, reconnect the glow plug connector removed above.  Wait for the glow plug light to go out and crnak the engine.  The engine will eventually start, but it may stall and run rough as the rest of the air is purged from the high pressure system.