Don't know whether an electrical vacuum would work overall or not. In the engine management the TPS & MAF sensors (among others) have pretty much done away with needing a vacuum sensor. So I would assume the computer doesn't need that information. But you could try just plugging it and see how that works. But my experience even with older classic cars is that 9 times out of ten when you find the problem it is obvious. Not pinholes in the line but a line either unplugged or cut in half.

For testing a MityVac (sp?) comes in handy. The better one is fairly cheap (under $100) and Horrible Freight used to carry a cheapy copy that is fine for testing for under $30.

I had the exact same problem pop up. Wound up being a hard line broken in the engine area.

 

Ok. So I went to the dealer today to buy a vacuum pump for a diesel X. It was $140 plus the power pigtail. Total out the door was $190. While the parts guy was getting the pigtail, there was a tech that overheard my conversation. I asked him if my thinking was ok and he asked if he could take a look. I wasnt going to turn him down. Well in about 3seconds, he showed me the correct tee to plug off. Well sure as hell. It fixed it. There is a solenoid for the 4x4 hubs right next to the vacuum canister that locks the hubs. Well that was what I unplugged when I installed the manual hubs. He said that even though I unplugged the power wire to the solenoid, the switch is common to go bad and still pull vacuum through. I capped the red line at the tee where it comes off the solenoid and the trouble is all fixed. I almost feel that I should go back and give something to thank him. It saved me the money that i almost spent for a pump.

 

I just ordered a new PVH solenoid from Tousley for about $55 shipped. Local dealer wanted $90+tax.

It took me a while to find my similar problem. It seems to be dependent on engine temperature. When cold, autolockers work fine and vacuum holds. When hot, I get a leak.