Re: V4 Vacuum Hose Question - Saab Vintage Models Bulletin Board - Saabnet.com
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Re: V4 Vacuum Hose Question
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Posted by spiv (more from spiv) on Wed, 20 Nov 2002 19:00:54 Share Post by Email
In Reply to: Re: V4 Vacuum Hose Question, Brian, Wed, 20 Nov 2002 14:48:58
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Depending on the year of your engine (which isn't necessarily the year of your car!) this could be for:

-- One chamber of dual-chamber distributor. By having one vacuum takeoff above the throttle plate and one below, the vacuum advance curve of the distributor became more sensitive to throttle position and engine load. The idea was to control emissions a bit better, but the dual-chamber distributor was kind of a pain in the tail and a lot of people have ditched it by now.

-- Same idea as above, but now the hose would go to the PVS (positive vacuum system) switch, a weird multi-pronged gizmo normally found either roosting on top of the thermostat housing or teed into the coolant line that feeds the choke heater. This let you have a single-chamber distributor again, and controlled the vacuum feed according to whether or not the engine was warmed up. Again, the idea was to provide a simple form of emission control that didn't steal power (unlike, say, an air pump) or require a lot of extra sensors and controls.

The system works pretty well (my car runs better with it than without it) so if your PVS valve is in good shape and you've got all the other plumbing, you might as well hook it up and use it. If your engine lacks the other PVS stuff, just cap the vacuum port and forget about it.

posted by 68.13.138...

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