Another possibility for this is that the vacuum check valve has either failed or isn't present. The ventilation system on most cars is usually controlled by manifold vacuum. On a long hill and under acceleration this diminishes, so there is usually a check valve in the system so that the heater door won't open and cause heat into the car on a hot day with the a/c on.
Some early '80s cars had poorly functioning check valves when new and did this sort of thing right off the show room floor. I don't think this would have been true of an Imperial, but since this car has had some related conversion work, the connections may not be correct, the valve may have been bypassed, or left out altogether. It worth looking into.
Paul W.
-----Original Message-----
From: Elijah Scott <
imperial1971@yahoo.com>
To: mailing-list@xxxxxxxxxxxxxxxx
Sent: Thu, 18 May 2006 05:48:14 -0700 (PDT)
Subject: Re:
IML: odd
vaccum-related behavior (82 Imperial)
Nat Hall <nathall@arno.com> wrote:
I haven't had a chance yet to play with finding out why my carb-converted '82 isn't passing the smog test, but in the meantime I've noticed something very odd. On hard acceleration, like on a freeway on-ramp with almost-full-throttle to full-throttle acceleration, if my A/C is on blowing out the dash panel vents, air flow direction will temporarily switch to blow exclusively from the floor vents (isn't this the "default" position?). Is this a result of a vaccum leak somewhere? If so, could this be a cause of my emissions test failure?
You may well have found the cause of your emissions test failure. The position of the vents is controlled by engine vacuum -- so if the air goes from the dash vents to the floor vents when you hit the gas, there is definitely a vacuum leak.
Tracking this down will likely be an exciting exercise in frustration. :o) You are most definitely going to need a shop manual with a schematic of the vacuum lines.
Or you may get lucky and spot it right away on a visual inspection. I would start with the simple stuff and get under the hood and look at every vacuum hose and connection that you can see.
Good luck!
Elijah
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