lgp9999

I think I have a vacuum leak. Heater controls and 4wd both work, but I've got oil spewing out of the engine and excessive crankcase pressure which leads me to believe that I have a vacuum leak somewhere.

First of all, is there a vacuum diagram for our trucks available?

Second, there is a vacuum line going up from the front differential area into the rear right side of the engine bay that has some sort of vent cap on it. What's that for? My best guess is that it provides a bypass so that the vacuum pump doesn't suck in water if the front diff gets submerged. If that's the case, can it become gunked up and stuck open causing a vacuum leak?

Tate

That line from the diff is the vent line for the diff, for when it heats and cools, so it doesn't pressurize and blow out seals. The CAD is run by a double acting cylinder, so there shouldn't be any venting into the diff AFAIK.

I would disconnect the vacuum lines from the pump, and then plug it off, and see if the symptoms go away. If it doesn't, you might be looking at a more serious issue.

lgp9999

Well I just put a hand vacuum pump with a gauge on it and it sure enough looks like I got a leak. Gonna go try to track it down.

lgp9999

Well I throughly tested the vacuum system. The rubber elbow off of the vacuum pump was pitted and leaking, also the rubber coupler piece that connected the main line from the pump to the line on the firewall was pitted and leaking. I replaced both. I also replaced the line that goes to the cruise control unit, as it had a big hole in it. The system held vacuum much better, although I don't think I'm completely done as there were small leaks where the vacuum bundle plugs into the transfer case, but that was very slight and the worst of it was taken care of.

Both in smoke from the breather, as well as smoke from the crank case when the oil cap is open, was much much less than previous! I'm on the right track here!

infidel

When it holds vacuum for an hour you'll be done.
A leakless system can easily hold vacuum for a week.

lgp9999

Every part I replaced will hold vacuum basically indefinitely. I need to do the rest, including the lines to the heater system, and the lines to the transfer case and front diff. Is the vacuum loom that plugs into the transfer case available anywhere?