I have a 6.2 L in a 1982 Winnebago. Firstly let me say I have had this rig for nearly 8 Mos with little problems with the engine till recently. I'm using the Haynes 6.2L Repair Manual. First off I started noticing that I needed to have the vacum assist switch to start it, not just when it was cold. then I accidently cracked the FROM the return of the Fuel Injecton pump, at that time I had a manual fuel pump, I bypassed it with a high volume electric pump I hooked up a plastic hose to the return and was able to see the air bubbles in the fuel move through, eventually they got smaller and stopped all together, I eventually got it started after bleediing 4 injector lines on one side and then the other side and changing the primary and secondary fuel filters which were sucking air as well. I found out that there was a crack in the TO line of the secondary fuel filter and it was sucking a little air. I drove it as is, it died after a block, started again and I could only drive it with the vacum switch out. After driving a few miles I couldn't start it again. I replaced that line, which had a cold start sensor on it, with just regular fuel hose, but I couldn't get it started so I was towed back and I have not been able to start it since. I have changed the manual pump and I just discovered I had two bad glow lplugs, which I have replaced. Someone told me that if you squirt WD40 and crank it should help the air out. One thing that is different is that Unless I crank the engine I don't see any fuel moving through the return like I did before I started it, also I notice that there is pressure at the fitting of the to line of the secondary filter, which is supposed to be symptomatic of a clogged fillter, but that can't be since It's very new. I'm at a loss. I'm suspicious of the EFI pump since it was overhauled about 4 years ago and the governor weight retainer ring is missing, The air and fuel only moves when you crank the engine. I tested the Roosa Master DB2 pump but just checking for the click as the book says, I don't have the gauge that is required to hook up to the tap to check the pressure and I don't know where to get one and the adapter, that is if I need it. I was told not to condemn the pump just yet, but I don't have any way to know if it's working right, although fuel and air do come out of the injector lines when you crank the motor. One thing I have not tested and suspect is the Fuel shut off solenoid, I really wonder why with a high pressure electric fuel pump and the EFI pump switch on that I don't see any fuel or air moving through the return line without cranking the motor, maybe I"m missing something? Will I be able to get this motor started again?
Sorry for so much info but I wanted to cover every detail, also sorry if this is off topic. Hope someone can help. :)
Thanks
Ken

Well I just replaced two glow plugs and now I"m getting some kind of combustion, I checked the primary fuel filter by loosening the petcock and I could hear air inside coming out, Is this a sign of air somewhere between the tank and the filter or is it just because the air has not been bled out of the whole system?
Thanks

Rig up your electric fuel pump to pressurize both fuel filters and your problem should diminish, plus it will help you find your air leak, because it will start leaking fuel.;)

Thanks for the reply and advice, I still have to replace the glow plugs the one that came out was a cav now delphi and it was 11.5 volts, I went to advance and got autolite 1110, but I still can't get any combustion with a little ether, Do I need to have at least 11.5 or 12, Chevy says it takes 12. Please help me figure it out.
Thanks :)

The Injection Pump (I.P.) is a mechanical device. The primary pump is a vane pump in the nose of the head. It only pumps fuel when turned by the engine. The hi-pressure side is also mechanical. It is a plunger, cam and roller pump. It also pumps when the engine is turning. This is why you won't see fuel moving when the electric lift pump is on and the engine is not turning. The electric pump supplies fuel to the primary pump inlet and, without it turning, the fuel stops in the head of the pump.

The only affect electricity has on the I.P. is to operate the fuel shut-off solenoid. If the solenoid is opening, the I.P. should work. You could remove the pump cover and visually inspect the operation of the shut-off solenoid but it usually is sufficient to power it up and listen for the slight click as you touch the wire to the shut-off terminal on the top of the pump.