Re: [DML] Re: PRV Catalytic Converters -- Volvo vs DeLorean

[William T Wilson <fluffy@xxxxxxxxxxx>]

On Wed, 10 Mar 2004, content22207 wrote:

> Other than the DeLorean, I've never seen a turn of the decade
> catalytic converter equipped vehicle without a smog pump from the

Almost every car has a smog pump.

The purpose of the smog pump on a catalytic converter equipped vehicle is
to provide additional air for the catalytic converter.  They call it a
smog pump, but it doesn't pump smog, it pumps ordinary air.  A catalytic
converter needs oxygen in order to convert unburned hydrocarbons into H2O
+ CO2.  Without a smog pump, it has to rely on the oxygen in the exhaust.  
There's some, but there's not enough.  Without it, the carbon builds up
inside the catalytic converter.  This reduces its effectiveness until
eventually it stops working.

There are catalytic converters in existence that are designed to work 
without this additional air.  They are almost all in aftermarket 
applications and typically do not last for more than a couple of years.  
The primary factors determining the success of a catalytic converter 
without a smog pump are the design of the cat, and the richness of the
mixture.  A too-rich mixture will eventually damage any cat, whether there 
is an air pump or not.

The reason cars with air pumps installed typically have a valve to 
control it is that too much air can cause the cat to overheat and can 
actually make it harder to convert nitrogen oxides.

Do not remove the smog pump on any vehicle.  They use less than 1 HP of 
power and without it you will have to replace your catalytic converter 
(unless you removed that too, but then you have no chance of passing 
emissions).

(Following quotes are from previous emails by other authors in the 
thread).

> fact is the Delorean runs so clean that it doesn't even need an
> exhaust gas recirculation system. Of course it does need to be

The primary purpose of exhaust gas recirculation is actually to lower 
combustion temperatures.  On a low compression car like the DeLorean, you 
don't need it.

> The great "catalytic converter stops up because mixture is too rich"
> vs "catalytic converter stops up because mixture is too lean" debate.

Both can damage the converter.  They are fairly robust devices, but they 
can still both plug up and overheat.




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