Catalytic Converter – Knowing The Basics And Testing

A catalytic converter is a device used to reduce the emissions from an internal combustion engine.

The catalytic converter works by breaking down unburned gases left over by the combustion process.

Catalytic Converter
Catalytic Converter

The exhaust from the engine gets filtered through this device and harmful chemicals are removed like:

  • Carbon monoxide (a poisonous gas)
  • Nitrogen oxides (a cause of smog and acid rain)
  • Hydrocarbons (a cause of smog)

A bad O2 sensor feeds wrong information to the computer which can affect the performance of catalytic converter.

Also, Too rich a fuel mixture causes unburnt fuel to enter the catalytic converter.

At some point it will be damage due to thermal shock.

Inside the converter, the gases flow through a dense honeycomb structure made from a ceramic and coated with the catalysts.

By using a honeycomb structure the area is greatly increased.

When something is wrong with your catalytic converter, it can cause a lot of problems.

One very important thing to note about catalytic converters is that they require you to use unleaded fuel. This is because the lead in conventional fuels “poisons” the catalyst and prevents it from working on the pollutants.

Also,  They only work at high temperatures when the engine has had chance to warm things up.

Check Engine Light And Codes

The check engine light (CEL) or malfunction indicator light (MIL) is your best friend when dealing with emission problems. Whenever this light comes on, check for trouble codes. The common catalyst failure code is P0420 or P0430, but check your code reader’s manual to be sure.

Signs Of Your Catalytic Converter Failing

There are a handful of telltale signs your catalytic converter is failing:

  • Poor acceleration when stepping on the gas pedal
  • Misfiring
  • Noticeably less fuel efficiency
  • Dark, sooty smoke exiting your muffler
  • Engine starting trouble
  • Failing an emissions test
  • A pungent sulfuric or rotten egg smell
  • A Check Engine light in conjunction with any of these other symptoms

Catalytic Converter Testing

An effective way to test for a blocked or clogged catalytic converter is with a vacuum gauge.

The Vacuum Test

Vacuum Gauge
Vacuum Gauge

An exhaust system restriction will cause a loss of engine power, but so can many other problems. If you suspect a plugged-up converter, you need to test the system. This test requires a vacuum gauge; if you don’t have one, consider buying one. A vacuum gauge is a useful diagnostic tool that will come in handy in other repair projects.

  • Set the transmission to park (automatic) or neutral (manual), and apply the parking brake.
  • Disconnect the vacuum hose at the brake power booster and connect the vacuum gauge to the hose or to another direct intake manifold port.
  • Start the engine and let it idle for about 15 to 20 minutes so that it reaches operating temperature.
  • At idle, vacuum reading should be between 18 and 22 in-Hg (inches of Mercury).
  • Increase and hold ending speed to about 3000rpm. Vacuum reading should drop but should go back to the previous level in a few seconds; otherwise, it’s likely the exhaust system is blocked. Continue to the next step.
  • Repeat the test, but this time, snap the throttle valve open about four times, rising engine speed to about 2500 rpm. Take note of the vacuum reading with each snap of the throttle.
  • So, If you see that gauge needle dropping steadily to near zero, most likely the catalytic converter or muffler is restricted.

  • To confirm a possible restriction, loosen the back pipe from the catalytic converter just enough to allow gas to flow through.
  • Repeat step 6. If vacuum doesn’t drop considerably this time, you’ve found the blockage (back pipe or muffler). Otherwise, go to the next step.
  • Loosen the header exhaust pipe from the converter just enough to allow exhaust gas to flow through.
  • Repeat step 6 and take note of your vacuum readings. If your vacuum readings show normal vacuum, the converter is restricted or clogged up.

Other Testing Options:

  • Loosen the catalytic converter from the header pipe or exhaust manifold. This allows gases to flow through. If you notice an improvement in engine performance, you are on the right track.
  • Just like the vacuum test above, a back pressure test can help you diagnose a clogged exhaust system. This test is done directly at the exhaust system to detect a plugged catalytic converter or muffler or pipe. This simple test requires a back pressure gauge.
  • Heat Gun
    Heat Gun
  • The temperature test using an infrared thermometer.
  • If the catalyst has stopped working, the front temperature will be about the same as the rear temperature.
  • In a good catalytic converter, the rear of the converter will be 20 degrees hotter than the front.

Conclusion

In most cases, the catalytic converter will last for the entire life cycle of a vehicle. While sturdy, the catalytic converter can slowly fail over time as the catalyst elements wear out. High mileage is not the only culprit, as failure could be due to an improperly operating engine.

Worn spark plugs, or burned and leaking exhaust valves, allow unburned fuel into the exhaust system. Consequently, It ignites in the catalytic converter and melts the internals. A weak ignition system can also cause the same problem, by not getting enough spark to the plugs.

Catalytic converter problems could also be something more serious, like heavily worn piston rings or jumped timing chain. These problems allow fuel or air into the wrong place at the wrong time. A head gasket or intake manifold leak can cause problems as well. As a result, oil or coolant can coat the catalyst, setting off a check engine light.

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