Information

Catalytic converters should not fail under normal operating conditions.
If it has the most likely cause is a problem with the car. The following
faults are not covered under the terms of our guarantee.

Road / Impact Damage

Impact damage is caused to the catalyst when it hits, or is struck by
hard objects. This can cause the monolith to fracture and the pieces
to rattle around inside the unit. Possible causes are a hard object
striking the converter, hitting speed bumps and off-road driving.
Impact damage can usually be seen with the naked eye on the
housing of the unit.

Plugged or Contaminated Monolith

This is when the monolith becomes coated and blocked with soot,
preventing it from converting the gases that pass through it. This can
be caused by the car running rich, using the incorrect fuel or
unsuitable fuel additives, and oil or antifreeze entering the exhaust.
Excessive levels of hydrocarbons (neat fuel) entering the exhaust can
also contaminate the monolith and prevent it working. Always ensure
that the vehicle is running at no higher than 55PPM HC before fitting
a new catalyst*.

Melted or Broken Monolith

Monoliths can be broken in a variety of ways, the most common
being impact damage (see section above). It can also be broken
when it suffers a sudden drop in temperature (e.g. driving through a
ford) as the steel shell contracts faster than the ceramic monolith as
it cools and crushes it. The monolith can be melted when unburned
fuel is injected into the catalyst. Causes of this are tow or bump
starting, or the car’s engine not firing properly on starting. More
information on the causes of melting monoliths can be found below.

Overheating

There are many problems that can cause a catalyst to overheat or
fail. The most common of these is when unburned fuel enters the
catalyst. This fuel ignites when it reaches the catalyst because of the
high operating temperatures, causing the catalyst to superheat and
melt down. Some causes of this are faulty spark plugs and leads,
which cause the engine to misfire, and a badly timed distributor.

Oxygen / Lambda Sensor

The oxygen (lambda) sensor collects and sends information to the
ECU (Electronic Control Unit). This is used to control the air/fuel mix. If
the oxygen sensor is faulty, the air/fuel mixture will not be corrected.
In the case of it running rich excess fuel will enter the catalyst, causing
it to superheat and melt down. It is advised that a new oxygen
sensor is fitted every time a catalyst is replaced.

Fuel Injection Systems

A catalyst can be damaged if a fuel injector is leaking internally or
dribbling fuel into the engine. The excess fuel will then enter the
exhaust system and superheat the catalyst, causing the monolith to
melt down.

Map Sensors

Map sensors inform the ECU of the load on the engine and the
amount of air entering it. If this sensor fails it causes a rich condition
in the engine, which can superheat the catalyst and cause it to fail.

Carburettor Systems

A worn or defective carburettor can cause a catalyst to overheat.
Problems such as improper float or air/fuel mix adjustments and worn
metering rods can damage the catalyst. The choke system also
needs to be operating properly so the right level of fuel enters the
system. If too much fuel enters the system the catalyst will overheat
and eventually fail.

Canister Purge Valve Control

This vacuum operated valve vents fuel vapour from the carburettor
bowl to the charcoal canister. If the vacuum is breached, the charcoal
canister will flood and the air/fuel mixture will become very rich. This
excess fuel will enter the catalyst and the monolith will melt down.

Noisy

A catalyst should not be considered to be a silencer although it does
have some silencing qualities. Noise can be caused by excessive
amounts of fuel getting into the converter.

*We will no longer accept emissions warranty returns without the relevant emissions
report. We will also not collect any catalysts for warranty claims with HC levels above
60ppm, except at the discretion of the technician.

Fitting Advice

Catalytic converters are not easy to fit. The following information
should be used as advice when fitting a catalytic converter.

1. Do not attempt to fit a catalyst unless you have experience in
   doing so. Catalysts are expensive items and any mistake could
   damage it.
2. Never use exhaust paste in front of the catalyst. This will
   immediately invalidate the guarantee.
3. Do not hit the catalytic converter with a mallet or hammer to try
   and force it into place. Doing so may fracture the monolith and
   invalidate the warranty.
4. Always use new fittings, such as gaskets, nuts and bolts
   wherever possible.
5. Always offer the catalyst to the vehicle to see if it will fit. If you
   believe the catalyst may have to be altered to fit, please call
   our technical department. You may have the wrong catalyst for
   your vehicle. Any alterations made without our authorisation will
   invalidate the warranty.
6. Always fit the unit loosely before making the final adjustments.
   It is then fine to tighten the unit at both ends. This will prevent
   fitting problems as tightening the front end fully before pushing
   the back end into place may result in a bad fit.
7. After fitting a new catalyst ensure the vehicle is run for 20
   minutes at fast idle (approx. 2000rpm) to allow the matting to
   expand and apply the correct pressure to the monolith. Failure
   to do this will result in the monolith detaching from the matting,
   causing the catalyst to rattle.