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Originally Posted by bearcat5
Remove the O2 from the exhaust; Put any kind of hollow adapter in place of O2. Attach a hose from the adapter to a pressure gauge. Start car and watch the pressure. You'll have to check the book to see what the back pressure should but from what I remember it shouldn’t be any more than 2lbs at any given RPM. If it is change the cat.
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Good suggestion. But here's some additional info for clarification:
The gauge needed for this method is a low pressure (0 - 5 psi) gauge.
After connecting test fixture, the engine should be warmed up to operating temperature and then rpms run up to 2000- 2500.
Note reading and if it reads greater than 1.25 psi, the CAT is clogged or the exhaust system backpressure is excessive.
BTW - This is in accordance with the GM service manual for the Buick Regal.