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How can one determine if their cat is clogged?

Does it need to be removed and visually inspected to see if any light passes through or is there an on vehicle test.

My 87 has 163k on it and I'm wondering if a new cat might wake it up some. I put on a 2 1/4" cat back with magnaflow on when the stock exhaust rotted and fell off and this has been a HUGE difference but the 4runner is heavy enough and since I'm at altitude I need all the power I can get.


The cheapest way to tell is just pull it off and look through it. If you can see light on the other side(about the size of a dime) than it is still good. If you fcan't, or it is rattling replace it with a new one. There is a bit of difference between the standard hi-flow cats and the the Magnaflow. There is a lot more light visible through a Magnaflow, and you can almost make out what you see, whereas you can't with a regular cat. However teh Magnaflows do cost a lot more.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed