Mystery Vacuum Hose: '78 280ce m110

[Ten13]

I've been sorting out a few minor issues with my '78 280ce, and have discovered a disconnected vacuum hose going to the fuel vapor recovery charcoal canister in the engine compartment. This is the one with the check valve inline between canister and engine. I see where it's supposed to go according to the diagram, but cannot find a place to connect it to, except for a vacuum fitting on the intake manifold, which is currently capped. See photos.

When I test-connect the hose to the capped fitting, the check valve vibrates and it seems to be creating a strong vacuum in the gas tank, evidenced by a loud CLUNK sound as the fuel tank pops back to it's normal size, when disconnected.

The car runs fine as-is, but I thought I'd reach out to see if I'm missing some fitting. I have looked and looked!

Thank you,
-greg fulcher

[rbtoj]

Ah an m110 vacuum issue!

That caped vacuum connector originally was connected to the distributor retard an cars made up to april 1978. After that, the distributor retard got it's vacuum signal from one of the idle air hoses under the intake manifold (you cannot see it without taking the intake out). Your car probably was updated soon after that, as the service manual describes this modification.
As for the hose, I only have an euro m110 so I cannot help with that. But it is definitely not connected to that capped plug.

[Rick76]

There are 2 ports on the throttle valve body closest to the engine. The upper one goes to the distributor and the lower larger one goes to the regenerating valve (purge valve) and then to the canister. See section 14.2-100 of the manual for more info.

[Ten13]

Originally Posted by Rick76

There are 2 ports on the throttle valve body closest to the engine. The upper one goes to the distributor and the lower larger one goes to the regenerating valve (purge valve) and then to the canister. See section 14.2-100 of the manual for more info.

Thanks, Rick76... I will poke around some more. Flashlights, mirrors, feeling around.. I haven't been able to find an open port. Maybe it's occupied incorrectly by something else. Cheers!