'77 Maverick with 250 AT I have a three port vacuum "loop" on the firewall. Not sure what that is, but it has the lower port connected to the Dual diaghram on the tranny, middle port connected to what looks like the charcoal cannister, upper port connected to the passenger side of the intake manifold. Anyone have any idea what this might be called in the service manual as it relates to the overall emission system/vacuum diagram? I have an idea of what it's function may be, although why it is connected to the charcoal cannister is not clear. Any ideas? Thank you in advance to all that reply!
I am not sure if what you see is what I am talking about, but I think one function is to pull a vacuum on the levers in your a/c-heater, which activate the little doors in your dash heat-ac venting system. The charcoal cannister is for venting of the gas tank, maybe a vacuum is needed on it to "assist" pressure regulation in the fuel system. I hope this (mis)information does not lead you astray.
Charcoal canister should not be hooked to a vacuum port. The small line on the canister is the vent to the tank and the big line goes to the air cleaner. If the small line is hooked to the vacuum, where is your tank vent?
Ref: Help with identifying part on engine That's a good question. I will have to check and let you know. So, the larger port on the charcoal cannister should be hooked to a breather element on the side of the air cleaner? The smaller one should go to the fuel tank. The guy I bought the car from disconnected and removed about half of the vacuum lines and left others open. So before I start this car up and kill the carb, I want to make sure all the vacuum lines and items are identified in the emission system so I do it right the first time. One of my other posts is a request for vacuum diagrams for the '77 Mav with the 250 AT with A/C. As an example, he had intake manifold vacuum hooked directly to the distributor vacuum advance with a red/black check valve installed in the middle. You could idle that thing, turn the curb idle all the way down and still have the engine running fast.
Don't mistake the charcoal cannister for the vacuum cannister. The vacuum cannister is the one that looks like a coffee can and will be mounted closer to the frame rail, the charcoal cannister has what looks like a canning pot lid on it with the flex hose (i'd say approx 3/4" diameter) coming out of the middle of the lid and then the other small line that connects to the hard line going to the gas tank.
