I know, I know you are expecting the same old vacuum line question about routing on the engine. But I think I have a new one. And I come bearing a picture! I have an open port behind the cruise control unit on the engine coming out of the passenger side fenderwell. Before I start tearing things apart to identify this guy I am hoping someone has it hooked up on their rig and can tell me where it goes? A quick trip through the service manual got me nothing so far.

Jake

 

Do you have a vac diagram on under side of hood?
IIRC both of those thru to fender go to the vacuum reservoir. One goes over to the manifold for vacuum power for all the vacuum needing things and the other goes I think to the switches for the ADD (a vacuum customer). I seem to remember also a set of vacuum valves on right fender that worked with some other stuff. Like a set of three (?) EGR maybe.

Unless you have a 2wd, then i don't know, even less than I pretend.

 

These lines are not on that schematic under the hood. I have the factory manual and I still cannot really discover what is going on. It is a 4WD.

Jake

 

Coopster is 99% correct. The fitting goes to a vacuum tank between the apron and the wheel liner. https://web.archive.org/web/20120424...26addcontr.pdf It allows you to shift the ADD into/out of 4wd with the accelerator depressed (little vacuum).

The "other" pin you're asking about is solid on my truck, and I suspect it's solid on yours as well. So nothing connects to it.

 

Thank you. I am going to take a closer look at it. Its not solid. I put a smoke machine to it and it did not take long for smoke to start coming from out of the fenderwell. Maybe its just open on the other side. Guess I am going to have to drop the fenderwell and see what is going on.

Jake

 

Scope, isn't that tank a sort of reservoir or something? I really don't understand how that vacuum stuff really works (or not!)
Thanks

 

Yeah, just like you said. Vacuum is highest (the pressure is lowest) at idle, when the pistons are pulling against a closed throttle plate. When you stomp on the gas, the throttle plate opens, and even though the pistons are moving faster the air has an easier path in, so the vacuum in the intake goes down (pressure up).

The ADD uses vacuum to actuate. At Wide Open Throttle, the intake doesn't have enough vacuum to do the job, so the reservoir stores up vacuum to use when needed.

Back in the day, vehicles (buses) used vacuum to drive the windshield wipers. The wipers would noticeably slow down while the bus accelerated.

Now imagine a turbo-charged vehicle. The intake goes from less than atmospheric (vacuum) all the way up to more than atmospheric as the turbo kicks in. My Dodge Conquest (Mitsubishi Starion) had an electric vacuum pump to back up the reservoir when needed.