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post #1 of 18 (permalink) Old 01-08-2009, 07:38 AM Thread Starter
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Question Cat replacement quote...options.

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)?

Last edited by ortbird; 01-08-2009 at 07:49 AM.
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post #2 of 18 (permalink) Old 01-08-2009, 07:56 AM
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Before I put in catalytic converters, I would install new O2 sensors that are behind the cats. (Actually I would replace all 4 just because the front ones probably need replacing anyway).

I've seen them go bad more often than I have seen the cats go bad, especially on a modern fuel injected car.

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post #3 of 18 (permalink) Old 01-08-2009, 07:58 AM
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Jezz 499.80 for one CAT !!!!!!!!!!!!!!!

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post #4 of 18 (permalink) Old 01-08-2009, 08:00 AM
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Quote:
Originally Posted by ThunderChecken View Post
Jezz 499.80 for one CAT !!!!!!!!!!!!!!!
That's the direct-fit catalyst pipe with all 3 cats.
That's a fair price for the work,and a fair price on the parts as well.
JL

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post #5 of 18 (permalink) Old 01-08-2009, 12:06 PM
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Originally Posted by Johnny Langton View Post
That's the direct-fit catalyst pipe with all 3 cats.
That's a fair price for the work,and a fair price on the parts as well.
JL
I agree.

Don't blame the oxygen sensors for the catalyst efficiency code. With the way the computer runs the catalyst efficiency test, a bad rear oxygen sensor really can't throw a false efficiency code.

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post #6 of 18 (permalink) Old 01-08-2009, 12:16 PM
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Quote:
Originally Posted by master486 View Post
Don't blame the oxygen sensors for the catalyst efficiency code. With the way the computer runs the catalyst efficiency test, a bad rear oxygen sensor really can't throw a false efficiency code.
Can you expand on how the computer runs the efficiency test and how a weak O2 sensor wouldn’t give that symptom.

Maybe I'm just a cheap bastard, but I still recommend replacing the O2 sensors to the tune of $120 (or less) before I dropped $740 for new cats AND O2 sensors.

Either way you end up with new sensors.

You guys that work on multiple cars: What has the higher failure rate: O2's or converters? I don't know, that why I'm asking.

But of course, just my opinion.

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post #7 of 18 (permalink) Old 01-08-2009, 12:21 PM
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If I ever get a O2 or Cat code anything, I always check the O2s first and replace. I would replace the two front sensors and reset the code.

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post #8 of 18 (permalink) Old 01-08-2009, 12:21 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L View Post
Can you expand on how the computer runs the efficiency test and how a weak O2 sensor wouldn’t give that symptom.

Maybe I'm just a cheap bastard, but I still recommend replacing the O2 sensors to the tune of $120 (or less) before I dropped $740 for new cats AND O2 sensors.

Either way you end up with new sensors.

You guys that work on multiple cars: What has the higher failure rate: O2's or converters? I don't know, that why I'm asking.

But of course, just my opinion.
Converters vs rear O2's-it's the converters.

'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.
JL

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post #9 of 18 (permalink) Old 01-08-2009, 12:23 PM
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Quote:
Originally Posted by OxmanWI View Post
If I ever get a O2 or Cat code anything, I always check the O2s first and replace. I would replace the two front sensors and reset the code.
The front sensors have absolutely nothing to do with a catalyst code.
JL

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post #10 of 18 (permalink) Old 01-08-2009, 12:38 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L View 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.

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post #11 of 18 (permalink) Old 01-08-2009, 12:39 PM
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Quote:
Originally Posted by Johnny Langton View Post
Converters vs rear O2's-it's the converters.

'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.
JL
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.

But this discussion got me thinking… So: http://forums.tccoa.com/showthread.php?t=118386

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post #12 of 18 (permalink) Old 01-08-2009, 12:41 PM
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Quote:
Originally Posted by Johnny Langton View Post
The front sensors have absolutely nothing to do with a catalyst code.
JL
Ok copy my mix up, then maybe the back O2s are not reading right or possibly a exhaust leak some where?

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post #13 of 18 (permalink) Old 01-08-2009, 12:52 PM
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Quote:
Originally Posted by Johnny Langton View Post
That's the direct-fit catalyst pipe with all 3 cats.
That's a fair price for the work,and a fair price on the parts as well.
JL
Thank you John for the info

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post #14 of 18 (permalink) Old 01-08-2009, 01:37 PM Thread Starter
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Thanks for the comments.

But I am confused now:

so some of you think that the rear O2's can falsely cause this code ?? (or Not?)

So should I ask the guy to check for faulty rear O2 sensors then ?

Or should I just go ahead and get everything done as I planned?
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post #15 of 18 (permalink) Old 01-08-2009, 03:10 PM
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You need the cats replaced. The rear sensors are not causing this code.

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post #16 of 18 (permalink) Old 01-08-2009, 03:35 PM
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Quote:
Originally Posted by master486 View Post
You need the cats replaced. The rear sensors are not causing this code.
Cause you would know, you checked his car out?

He's showing a P0430 OBD-II Trouble Code

Acording to OBD-Codes.com you should check for exhaust leaks, rear 02s, then continue to the cats.

http://www.obd-codes.com/trouble_cod...old-bank-2.php

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post #17 of 18 (permalink) Old 01-08-2009, 04:29 PM
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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.

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post #18 of 18 (permalink) Old 01-08-2009, 05:46 PM
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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.

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