Catalytic Conveter Diagnosis HELP!

[srmmmm]

You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration

[amancuso]

Originally Posted by srmmmm

You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration

OOO thank you. So far 200 miles and no CEL. I ran a bottle of LiquiMoly engine and exhaust cleaner through, so, we'll see.

[oldskewel]

Originally Posted by srmmmm

You can get these nice spacers from FCP:


https://www.fcpeuro.com/products/uni...roducts-o2pair


I'm tempted to try them myself.


2002 X5 3.0 378,900 miles
2014 428i 68,000 miles


2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles


1970 Firebird Under restoration

Interesting looking design there. It makes a lot more sense than some of the more compact ones, although I realize in many cases stealth is a big factor and these are definitely not that.

My basic understanding of how they work, which may help answer some of the questions in this thread:

They only go on the downstream, post-cat O2 sensors.

The reason they work is that they create a mixing volume of exhaust gas that effectively averages out the exhaust gas coming through. So these ones shown here look good since they have a bigger volume (in that big fat elbow) in which the gas can accumulate and mix. They also appear to have a selection of orifices to choose from to tune how fast new gas will be cycled through there.

Basically fuel injection systems close the loop on air fuel ratio by switching back and forth between slightly too lean and slightly too rich. So the upstream O2 sensors will bang high/low at a controlled frequency, like 1 Hz or so. Then the cat converter is supposed to take those imperfect ratios and let them complete combustion within the cat, so that what comes out is a smooth signal, no longer oscillating up and down.

If a cat has truly lost its ability to catalyze those reactions, the gas coming out of the cat will be fluctuating high-low-O2 just like the upstream input. The downstream O2 sensor looks for this (an oscillation rather than the desired steady signal) and triggers the P0420 or P0430 to say the cat is not working right.

The extender things capture a little volume of gas, letting it average itself out and giving it some time to complete combustion, hopefully keeping the downstream O2 sensor readings steady.

The P0420 detection algorithm is notoriously inaccurate. You may find that installing an extender like this solves the code problems, and you still pass the sniffer test in a smog check - confirming that there was no true cat issue to begin with.