so I've been running around with the "catalyst efficicency below threshold - bank 2" CEL for about 2 yrr, and a local place that specializes in Fords (the guy who runs it is a former Ford Master Tech) gave me a quote to replace cats and O2 sensors (total with parts+labor)...
here's his email to me and his quote for ALL 3 CATS and O2 sensors:
"....I would say from your description of the problem that you are correct, and the car needs new catalytic convertors. I have not gotten good reliability out of universal weld in cats, and would suggest using a direct fit replacement. I have attached a quote for replacing the convertors and oxygen sensors, which includes a Walker direct fit convertor setup. I can usually get a magnaflow setup for a similar price if you are interested...."
what do you guys think ?? is this a good price ?
should I go walker or Magnaflow (same/similar price he says)?
Originally Posted by 94 Daily Driven 4.6LView Post
Can you expand on how the computer runs the efficiency test and how a weak O2 sensor wouldn’t give that symptom.
The PCM tests the cats by monitoring the switching frequency of the rear sensors. Before doing so it monitors the front sensors and their switching frequency. The rear sensors must have a switching frequency that is a calibrated amount less than the front sensors for the catalyst test to pass. The reason is that when the catalyst is working properly, it is able to retain oxygen and therefore the oxygen content before the cat is a lot greater than after, thus meaning the front sensors would switch faster. If the catalyst is not working properly, the oxygen content will be very similar both before and after the cat, thus the switching frequencies would be similar. Now, if the front sensors are older and switch slower than the rears, the PCM will detect the rears switching faster than the fronts and set a code. There is no way the rears could switch faster than the fronts if everything is working right because more oxygen isn't introduced into the exhaust after passing by the front sensor. Also, there is a threshold that the front oxygen sensors must meet in their switching frequency or a code will be set for that as well. If the rear sensors are older and switch slower, this would actually work in favor of the catalyst test (by reading above and seeing the method of the test, you can see why), but the PCM does still test the rear sensors because it also temporarily switches fuel trim control to the rear sensors and monitors the results with the fronts to make sure it is within specification. So ultimately, if the sensors are faulty, the catalyst efficiency test wouldn't falsely fail.
'98 F150-220K miles
'01 Navigator-160K miles
'01 F150-198K miles
'97 Expy-335K miles
'02 Expy-192K miles
All of the above vehicles have the original rear O2's, and we've replaced converters on 2 of them.
That's interesting, I'm the exact opposite:
94 T'bird: 200K miles
97 LSC: 145K miles
96 Grand Marquis: 126K miles
All of the above vehicles have the original converters, and I’ve had to replace the rear O2’s on all of them at least once (My Aspire is still chugging along with 205K and no O2 or converter failure yet… knock on wood!!).
Of all the cars I've owned, I have never had to replace a converter due to inefficiency. Broken internals, clogged, etc., sure, but never with an efficiency problem.
Got a code for pass side converter below threshold some years ago on my black car with less than 100k on it. Replacing the rear o2 sensor did solve the problem until the converter came apart. Note that when it did fall apart it never set a code for below efficiency.
Black '97 XR7
Magnaflow almost true duals w/ 3" rolled tips
Transgo bucking kit w/ aux cooler
If your pulling a P0420 or a P0430 its the cats, not the O2 sensor. I got my cats from magnaflow for 270, and it cost 50 bucks to put it on so job total I have about $320 in it, less than half of what you were quoted.