[s-cars] Cleaning of Catalytic Converters (Katalysators) ?

[CyberPoet]

The catalytic converters' top (inner) surface of the catalytic material
is a very thin layer of platinum. In theory, you should be able to
clean them with almost any chemical compound that won't effect platinum
but will effect carbon. The reality is actually not so nice...

If your O2 sensors were broken/really bad, then normally the system is
prone to running excessively rich because of the timing advance
position (which is normally controlled in large part by the data from
the O2 sensors, which check how complete the burn is). This richness
can mean that unburnt (more correctly: incompletely burnt) fuel reached
the exhaust system while still burning, which in turn would raise the
exhaust system temperatures enough in a short period to melt the
substrate (die Unterstützungsmaterial) beneath the platinum and cause a
whole mess of problems (from a failed emissions report, to a blocked
exhaust from the actual melted substrate -- the last happened to me
once in a volvo 740; it was like someone sticking a potato in the
exhaust pipe). Glowing red-hot exhaust headers is a perfect indication
this is happening.

Carbon normally only builds up in a detrimental way on two general
surfaces, both of which are exposed directly to the combustion -- the
interior of the cylinder (including the valve faces), and sometimes the
first inch or two of exhaust pathway (a small part of the rear of the
exhaust valve & the beginning of the exhaust manifold/header). It would
not normally make it's way to the catalytic converter unless it was
fine enough to blow by the catalytic converter in the first place.
Additionally, if you have bad rings or bad valve seals, partially burnt
fuel can cause carbon build-up on other, less expected surfaces. Carbon
build-up is critical only because once heated, it will have a tendency
to act as charcoal and pre-ignite fuels during the compression
sequence. Since there is often some overlap between the intake and
exhaust valve 'open' periods, heavy carbon build-up on the back of the
exhaust valve and in the very start of the exhaust manifold can be
problematic when coupled with an ineffective O2 sensor by the virtue of
the overlap being too long.

There are ways to remove carbon build-up from the cylinder (both
physical methods, such as a cylinder hone, and chemical method, such as
certain injector-fed chemicals). The chemical method for removing heavy
carbon build-up is not good for your catalytic converters because it
runs the cylinder and the start of the exhaust extremely hot & polluted
(normally, you would remove your cats before using such a chemical at
full strength, again because of the threat of overheating the catalytic
converters). Most premium gasolines also contain detergents designed to
help prevent carbon build-up and remove existing carbon build-up,
albeit very slowly (since it is a weak concentration). Either way,
neither is a solution for cleaning a catalytic converter, which is what
you were seeking to start with.

Best Wishes,
=-= Marc Glasgow
www.cyberpoet.net


Joern Wrote:

I have two used RS2 cats that has been driven for a while with a broken
O2
sensor and is in my opinion contaminated with carbons, but I would like
to use
them on my car if I could get them cleaned.

Is there any way to clean used cats either mechanically or by
solvent/chemicals?

Anybody with some experience in cleaning?