Tech Stuff

Catalytic converter diagnosis

A catalytic converter cutaway showing the matting and ceramic brick.
<p>A catalytic converter cutaway showing the matting and ceramic brick.</p>

Catalytic converter break-in

That’s right — a replacement catalytic converter needs a proper “break-in” period, just like a new engine or a set of new brake pads. This will ensure that the cat will continue to work the way it is supposed to and deliver the required emissions reliability and long service life. If the converter is not warmed-up (broken-in) properly, the substrate inside could be adversely affected and eventually cause the converter to fail down the road.

The problem typically occurs when a shop installs the converter and immediately returns the vehicle to the customer. The customer drives away and runs the car for a long distance or lets the vehicle idle for an extended period of time. Under these conditions, the matting, which is intended to secure the substrate, will not expand properly and hold it in place.

Converter matting is made from a mineral called vermiculite, which is held together by a fiber mat and an organic binder. This matting is wrapped around the converter’s ceramic brick (see art on page 20).

The matting is installed in the converter in an unexpanded state. During the first heat-up, the fiber mat and binder burn off and the matting actually gets looser before it expands to fill the converter cavity to hold the ceramic brick in place (see graph below).

An example of how matting thickness relates to expansion temperature.
<p>An example of how matting thickness relates to expansion temperature.</p>

If that warm-up is not done properly, the brick can come loose and get damaged.

That rattle you might hear inside the converter shell is a sure telltale sign for this problem.

Warm up the cat

The best way to avoid this service issue and potential warranty problems is to include the warm-up period as a key part of your overall converter installation procedure. This heating cycle will allow for correct matting expansion.

Converter break-in tips

• Start the engine but do not rev the engine.

• Idle the engine and allow it to warm up slowly.

• After five minutes, increase the engine speed to 2,500 rpm.

• Hold at 2,500 rpm for two minutes.

• Allow the engine to cool down.

• Road test to confirm correct installation. ●

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