How To Check Out Your Car’s Catalytic Converter for Blockage

Your car functions because it burns fuel.  The burning of fuel leaves behind by-products such as hydrocarbons and carbon monoxide that could accumulate in your car’s internals.  Your car’s catalytic converter cleans up those by-products—except when the converter is damaged or clogged.  If it is, your vehicle’s engine may not perform optimally and may even fail an emissions test.  Clogging in the catalytic converter restricts airflow in the exhaust.  The result:  increase in back pressure, which contributes to a fast decrease in your engine’s performance and poorer burning of fuel.  Especially if the clogging is severe, your engine may stall after starting it, or it simply may not start at all.  This article will help you check for blockage in your car’s catalytic converter.

With a vacuum gauge, you can easily find out if your catalytic converter has a blockage.  Attach the gauge to the intake manifold.  There is intake vacuum inside the manifold that your gauge will check for pressure.  Other points where you can attach the vacuum gauge are the carburetor and throttle body.  Intake vacuum is created in the intake manifold because of the pressure discrepancy from the pumping of the engine’s pistons and the restriction from the throttle valve.  Get the pressure reading on the gauge when the engine is idle.  Then, increase the engine speed to about 2,500 and keep it at that speed.  When you first release the throttle, the gauge pointer will fall fast but it will go back up and should remain steady at some point.  If it drops again after rising, the exhaust system may be building up back pressure.

Another method you can try is direct measurement of back pressure.  What you want to find out is how much pressure is present at a specific speed.  Here’s how to find out.  Locate the check valve on the distribution manifold and detach it.  In its place, attach a low-pressure gauge.  As an alternative, you can detach the oxygen sensor and attach the low-pressure gauge in its place in the manifold or headpipe.  Your low-pressure gauge usually has instructions or specifications for using it, including the varying amounts of pressure at varying engine speeds; so, you might want to read up before starting.  Generally, if you get a PSI reading of 1.25 when the engine is running idly, or a PSI of more than 3.00 when the engine speed reaches 2,000 RPM, you could relatively conclude that your catalytic converter has a blockage.

A third method involves drilling holes in the front and back of the catalytic converter.  The converter is located in the underside of your car.  Consult your car’s service manual if you need to find it quickly.  Jack up your car so that you can easily access the converter.  Using a drill, bore a hole about ¼ of an inch big in the pipe’s exhaust, just right in the back of the catalytic converter.  Attach a pressure gauge to the hole.  Start the car and take a reading on the pressure gauge.  A low pressure reading at the back of the catalytic converter is not something to worry about.  A high pressure reading is—and it is usually also a signal for you to change your catalytic converter.

Check also the pressure in front of the catalytic converter.  The procedure is the same as in checking for the pressure in the back of the converter.

Making sure that your vehicle’s catalytic converter is free of blockage is very much like making sure that your nose is not clogged.  The results of blockage in the catalytic converter are very much like those of having a congested nose—your body cannot function efficiently and smoothly.  Therefore, always check whether your vehicle’s catalytic converter is clogged or not.


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