GMC 25170656 3-Way Catalytic Convertor Assembly (W/ Exhaust Rear Man

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To check if a catalytic converter is restricted, you can use a vacuum gauge to diagnose the effect of a blocked exhaust on intake vacuum. Here are the steps:Connect a vacuum gauge to an intake manifold vacuum source.Warm the engine to operating temperature and place the transmission in Park with the parking brake applied.Note and record the vacuum reading at idle.Open the throttle until the engine speed reaches about 2000 rpm.Quickly release the throttle and record the vacuum reading.Perform this test three more times, recording the reading after each test.If the reading after the fourth test is more than one inch of mercury (in-Hg) lower than the idle reading, it may indicate a clogged or restricted catalytic converter, muffler, or exhaust pipes.

If you suspect that the catalytic converter on your vehicle is malfunctioning, it is advisable to take it to a dealer or authorized emissions inspection facility for diagnosis and repair.