RE: IML: odd vaccum-related behavior (82 Imperial)

["Dick Benjamin" <dickb@xxxxxxxxx>]

Nat, this is a sign that your intake manifold vacuum is decreasing when you
are asking the engine for maximum power. This will happen on any engine, but
if the engine is worn, the effect will be much more severe.  If you have a
vacuum gauge, temporarily disconnect one of the hoses from a vacuum fitting
on the intake manifold and measure the vacuum at idle.  Depending on your
altitude, the ideal reading should be around 21 in. Hg.; lower at higher
altitude by about 1 in. Hg. for each 1000 feet (Less air pressing down, you
know!).  

If your vacuum at idle is OK, you don't have a serious vacuum leak.  If it
is a bit low, your engine is in need of a run on an engine analyzer to find
the cause.  I've forgotten how many miles on this car, but if it is up in
the 6 digit area, this is to be expected.

In other words, what you experience is not a malfunction other than a sign
of a worn engine.

If you don't have a vacuum gauge, you can try the poor man's check for a
vacuum leak as follows:  with the engine fully warm and idling peacefully,
slowly restrict air flow into the air cleaner with your hand, very slowly
increasing the restriction until you hear the engine either speed up or slow
down.  If it speeds up at all, it has a lean mixture at idle, which could be
a misadjusted carburetor idle mixture control, or it could be a vacuum leak.
If it just slows down as you restrict the air flow, you don't have a vacuum
leak.

Dick Benjamin

-----Original Message-----
From: mailing-list-owner@xxxxxxxxxxxxxxxx
[mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of Nat Hall
Sent: Wednesday, May 17, 2006 8:28 PM
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: IML: odd vaccum-related behavior (82 Imperial)

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?). Since the air flow
direction of the climate control system is a vaccum assisted/controlled
system, it seems to me like this is a result of a lack of vaccum. This is
reproducable 100% of the time and has happened many times over the last
week. As soon as my desired cruising speed is reached, and I ease off the
accelerator, the airflow direction will quickly return to the dash vents. I
have to believe this is not normal.

Is this a result of a vaccum leak somewhere? If so, could this be a cause
of my emissions test failure?


-------------------
Nat Hall
1982 Imperial Coupe
-------------------




-----------------  http://www.imperialclub.com  -----------------
This message was sent to you by the Imperial Mailing List. Please 
reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be 
shared with everyone. Private messages (and attachments) for the
Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx
To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm





-----------------  http://www.imperialclub.com  -----------------
This message was sent to you by the Imperial Mailing List. Please 
reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be 
shared with everyone. Private messages (and attachments) for the
Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx
To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm