1991 Freightliner fuel vac gauge is disconnected need help with diagram

It is a fuel restriction gauge. I am assuming it doesn't have a fitting on the back for a fuel line?

 

Pretty sure the line is supposed to be connected to the pump side of the primary fuel filter base/head. Like this.

 

The older trucks are set up that way. My truck has the same thing and my oil pressure guage has an oil line going to it. A few years ago, my oil pressure sensor started leaking and made a mess before I discovered it.

 

More likely that line was cracked and introduced air into fuel line, they eliminated the hose and port for it after pressurizing the tank and spilling fuel into the cab (only happens if fuel is under pressure, which only happens when you pressurize the tank to track the leak)

I have done that, a smarter thing would have been to disconnect the hose at the port (near water seperator) and cap it, if problem solved, test gauge and hose out of truck. Its very safe and fine if its done right, I was not that smart at the time

 

You really don't have to call the dealer.

You just need a length of air line whatever that is a quarter inch or whatever and you need the correct fitting at the filter.

You could probably get 10 ft of Airline and whatever fittings and ferrels and whatnot that you need and the whole thing probably will cost10 bucks or so.

 

I didn’t think it was a fuel line, just an air line. When pump pulls fuel from the filter, it pulls an air suction, connected to a sealed diaphragm of some sort in the gauge. No air gets into fuel since it’s sealed. When fuel filter gets restricted, gauge goes up, same principle as the air filter gauge. It would suck air if it were leaking, not leak fuel. Pressuring the fuel tanks, would probably push fuel into it. If it’s good, trapped air would keep fuel from getting into the gauge. Once it’s running, any fuel in the line would be siphoned out by the pump. Like @skallagrime said, if the line or gauge had a leak, it would push fuel out at the leak. Mechanical oil gauge is a different story, if the line gets chafed and leaks, pressurized oil will squirt out all over the inside of dash, and floor.