What Car Owners Need to Know About Using an Exhaust Test Pipe

Exhaust test pipes can be a useful tool in diagnosing certain exhaust and emission problems with late model vehicles. A clogged or restricted exhaust can restrict engine performance and may possibly damage critical engine control parts. An exhaust test pipe is usually installed in the exhaust system in place of the catalytic converter to determine if the converter is damaged internally. The catalyst in the converter can break apart and restrict exhaust flow. The catalyst can become clogged if an excessive amount of unburned fuel passes or engine oil that has leaked into the combustion chamber is then passed into the exhaust system.

DO: Use an exhaust test pipe if you suspect the exhaust is restricted

A restricted exhaust will cause the engine to lose power and the vehicle will be very slow to accelerate. Remove the catalytic converter, install the test pipe, and drive the vehicle. If performance returns to normal, then the diagnosis of a clogged converter is confirmed. If performance is still impaired, look for other reasons that could cause the problem.

DO: Check the entire exhaust system

If the test pipe fails to confirm that the catalytic converter is not the source of the problem, it is still possible the exhaust could be restricted in another location. The muffler baffles will seldom cause a serious restriction, even if broken, but a crushed muffler or even a crushed exhaust pipe can produce the same symptoms as a clogged converter.

DO: Check for other possible problems

If the exhaust system is intact without damaged or crushed parts there are other components that can cause similar symptoms. The engine intake has to breathe, as well as the exhaust; a plugged air intake, air filter, or damaged air duct can produce similar symptoms to a restricted exhaust. A transmission that is beginning to fail can also cause a lack of proper acceleration; restrictions in the fuel system, like a clogged fuel filter or damaged fuel line, may also contribute to decreased engine power.

DON’T: Leave the test pipe in the exhaust

The test pipe is a diagnostic tool and cannot be used to replace the catalytic converter. The converter is an essential component in the emission control system and greatly reduces the amount of harmful exhaust gasses released into the atmosphere. Severe penalties can be imposed on a shop owner or vehicle owner that replaces a catalytic converter permanently with an exhaust test pipe.

DON’T: Replace the converter with an inferior substitute

Some exhaust vendors produce replacement parts that can be bolted on in place of the catalytic converter that are little more than a second muffler for the exhaust. Without the proper catalyst in the converter, it will not perform as intended. While an inferior substitute may appear to look like a stock catalytic converter if it does not reduce emission to the required level, the vehicle owner may still be subject to fines and penalties for bypassing emission control laws.

DON’T: Use a replacement converter that cannot accommodate factory sensors

Many catalytic converters have ports for one or more oxygen sensors to be installed on the converter. An oxygen sensor measures the amount of emissions that enter the converter and in some cases exit the converter. Without the input from the oxygen sensor, the engine control module will not provide the proper amount of gas to the fuel injectors and the engine may run rich or lean. Damage to internal engine components will likely result and the vehicle will not operate in an efficient manner, wasting gas while continuing to create excessive emissions.

While the exhaust test pipe can help to pinpoint the cause of an exhaust restriction, the pipe cannot act as a replacement for the catalytic converter. The emission control system on a vehicle is important to help protect the environment. But emission controls are so interlinked to engine performance that eliminating a component from the system is going to have dire effects on the way the vehicle performs. The exhaust test pipe can be used to diagnose a problem, but the exhaust must be returned to its original configuration in order for the vehicle to perform as designed.