Re: cataltic converter

He's thinking of back pressure from a clogged cat. When this happens, exhaust gas isn't scavenged from the cylinders and power loss results. I once drove a BMW with a clogged cat and the damned thing wouldn't climb
hills faster than a '50 Ford.
The easiest way to check for a clogged up cat is to use a simple vacuum gauge connected to the O2 sensor port. Unscrew the sensor, and screw in an adaptor. Connect the vacuum gauge and bring the engine up to 1500 rpm. Normal reading is 0 psi on the gauge. If the pressure rises above 3 psi, the cat is clogged.
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On Fri, 22 Dec 2006 13:55:48 +0100 (CET), George Orwell

On an OBD2 vehicle the CEL will come on long before you feel any loss of power from a clogged cat.
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<clare at snyder.on.ca> wrote in message wrote:

It often will, but not always - all the OBDII knows about is whether it thinks the cat is working with the gases that make it through. The cat can be largely melted without triggering the cat codes, with some systems being much sensitive than others.
The Haynes manual for my daughter's Honda (of all places) has a good test for exhaust restriction: Connect a manifold guage to the intake manifold and note the reading at idle. Raise the throttle to about 2000 rpm for a few seconds and watch the guage as you release the throttle. It should return to the idle reading within two seconds. If it hangs at the higher pressure for several seconds or if it gradually returns to the idle reading you are seeing the effects of back pressure.
I like this method because it is quick and doesn't involve dealing with the exhaust.
Mike
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On Fri, 22 Dec 2006 13:22:39 -0700, "Michael Pardee"

Good test - but I've NEVER seen a melted down cat function well enough in the oxidizing mode to satisfy OBD2. Usually a melted cat has had the CEL on for more than a few miles at some point in it's life, because they GENERALLY only melt down if there are other emission related problems that turn the CEL on - like running WAY tto rich.
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