locating a vaccuum leak

New to the list here. From what I've read it seems you folkz are pretty
informed.
So here's my situation:
I have a '96 civic DX HB with about 85k miles. last week, literally
hours before I was gonna have her inspected, the check engine light
comes on. Following the guidance I've gleamed from here, I took it to
advanced auto and had them run the diagnostic.
The resulting code reads:
P0420
Catalyst Efficiency
Below Threshold
(Bank 1)

the lady who ran the diagnostic, said it was a vaccuum leak. So my
question to the group is; a) does this code give any indication of
where the leak is? if so, can you tell me where or point me to a
resource that can. b) how does one go about checking the vaccuum on
individual lines?

thanks in advance,

 

You can usually hear a vacuum leak - listen for a whistling or hissing noise
under the hood while at idle. For an example, blow through a small straw - it
will likely sound something like that. If you can hear the leak, but are having
trouble locating it, use a pair of needlenose pliers to (gently!) pinch off each
hose until the sound goes away - that will be your faulty hose, or the hose
running to a faulty vacuum device (sometimes the diaphragms in vacuum-operated
devices can become leaky).

Hope that helps..

 

The problem is more likely a worn out catalytic converter. There is a slight
possibility that an O2 sensor is bad. You will need a lot more knowledge to
troubleshoot the problem. You can spend a fortune throwing parts at it for
that code. There may be secondary codes in the computer that will further
define the problem. These you won't get from a parts store. I advise taking
it to a good mechanic and have it diagnosed properly.

 

Not a vacuum leak, but an AIR leak in the exhaust between the primary O2
sensor and the front of the cat. A garage that can do a "smoke test" can
eliminate this as a possibility.

Sometimes this is due to a cracked exhaust manifold, which is what creates
the air leak. Smoke test applies here too.

Many times it IS actually a cat that is not condensing as it should, and
needs to be replaced.

What sort of driving do you do? Lots of low-speed city? A mix?