Quote:
Originally Posted by Ruination Fan
You can try taking out the upstream o2 sensors (the ones right after the front cat)....
|
If you are testing for an obstructed cat it seems like you would want to remove the O2 sensors that were located before the converter, not the ones that are located after the converter.
I agree with this diagnosis, but a better test is to use a threaded adapter that screws into the front O2 mount to check the exhaust system back pressure before the front cats. At idle you should only see 1-2 PSI and at full-throttle the pressure shouldn't rise to more than 5-6 PSI.
I also agree with the other posts about an air-mass meter being a probable cause, adaptations should be checked to rule that one out before looking at the converters.
If the cat is plugged you'll see back pressure in the hundred PSI range before the engine starts to bog down, the test is pretty easy and its definitive.
I recently replaced the converters in a CLK430 and I was unimpressed with the quality of the OEM converters. The assembly is beautifully done in stainless steel but the converter matrix assembly is held internally in place with a couple of pinch points that are created by an external crimp to the converter case. If one or two of these pinch-points fail, or the converter fractures slightly the entire assembly will rattle around inside the converter. A good test is to jack-up the car and lightly tap the converter assemblies, if you can hear rattles that's not a good sign.