Porsche Cayman S catalyst and O2 DTCs.

I have a long story about catalyst efficiency DTCs on the 2006 Cayman S.  It starts back when I bought the car in 2014.  You can see that story here.  It had 60k miles on it when I bought it.  The car had a P0421 DTC which means "Warm Up Catalyst Efficiency Below Threshold (Bank 1)".  On this car that is the passengers side.  I installed an O2 bung on the muffler on that side and moved the downstream sensor there which generally eliminated that DTC, but I would occasionally get a DTC for the front sensor of that back stuck rich.  It would set that DTC randomly but not very often.

It did get annoying to have this DTC trip though, and I wanted to upgrade to better headers so I finally did in 2019.  I put the bank 1 downstream sensor back in the proper position when I installed the headers. The DTCs were finally gone for good, or so I thought.  I went to a track weekend in April just a month after installing the headers and I had no issues.  However, I went back to then same track in October and the car tripped the P0421 and P0431 ("Warm Up Catalyst Efficiency Below Threshold (Bank 2)") after idling for extended periods during warm-up.  Normally I just start the car and drive off but at the track the car sits and gets cold between sessions and I needed to get it fully warmed up before entering the track so I would idle it for much longer than normal.  It appeared the Fabspeed headers, in combination with this cold idle warm-up, was enough to fail the warm-up efficiency test. 

I suspect that these headers with the high-flow catalysts and larger, somewhat longer primary tubed are not as good at heating the catalyst, and that catalysts are enough less efficient that the test is below the threshold at times.  One of the known ways people get around this is by adding a spacer to the downstream O2 sensors.  This simulates catalyst oxygen storage to some degree and can help the test pass.  So, I installed some short straight extensions I bought through Amazon for cheap.

After installing these, I immediately got a DTC P2198 "O2 Sensor Signal Stuck Rich Bank 2 Sensor 1".  Since the car now has 87k miles on it, I replaced both the bank 2 O2 sensors but the P2198 remained.  I noticed the bank 2 upstream O2 sensor was loose when I went to replace it.  I checked and cleaned the MAF sensor, checked for vacuum leaks, re-torqued the headers and checked for exhaust leaks, and all was good.  Finally I removed the bank 2 downstream O2 extension and the P2198 went away and my O2 and catalyst monitors tested and passed (monitors were ready and no DTCs).  

Now, with an O2 extension in bank 1 but not in bank 2, I get these OBD test results (mode $06)

when the P0431 is pending.

Test report:
------------------
TID:$01 CID:$05
- Rich to Lean sensor threshold voltage(constant)
Min: 4,096
Test result value: 15,458
PASS
----
TID:$01 CID:$06
- Rich to Lean sensor threshold voltage(constant)
Min: 4,096
Test result value: 3,639
FAIL

I can't currently find the definitions of these but given that my pending DTC is P0431 I am presuming that CID $05 is bank 1 (which passed) and $06 is bank 2 (which failed and set the DTC pending.  You can see the large difference in test result values here.  The sensor without the extension is 89% of what it needs to be to pass whereas the other bank is 377%.  All other test results in the report passed.

I bought some shorter spacers and installed one in bank 2 only. 

I cleared DTCs and drove the car again, including cold start.  The P0431 sets pending again.  Here are the OBD test results this time:

Test report:

------------------

TID:$01 CID:$05

- Rich to Lean sensor threshold voltage(constant)

Min: 4,096

Test result value: 13,902

PASS

----

TID:$01 CID:$06

- Rich to Lean sensor threshold voltage(constant)

Min: 4,096

Test result value: 803

FAIL 

Strange how it is even worse with the spacer in bank 2.   Also interesting how the medium spacer works well in bank 1 but not in bank 2.  

It seems like my bank 2 catalyst is very weak, at least for the warm-up catalyst test.  

It is strange that I installed the headers March 2019.  I did not mature any DTCs for months of daily driving.  I did not check monitor readiness and did not check for pending DTCs however.  I did a PCA track weekend at Putnam that April and had no issues (that I recall anyway).  I went back to Putnam again October 2019 and that is when the DTCs started tripping pretty often.  Sometimes just one bank, other times both.  It would happen when I warmed up the car and would sit on the grid for long periods.  Since then I have had the P0421 and P0431 keep happening.  Now it is pretty consistent on bank 2..  

I drilled my original longer spacer out to 3/8".  I cleared the DTCs and drove the car.  After about 20 minutes of driving it finally tripped the P2198 again.  I cleared the DTCs, waited a few hours and drove the car again.  This time it completed all the monitors with no DTCs.  Here is my OBD Test results from that drive.

Test report:
------------------
TID:$01 CID:$05
- Rich to Lean sensor threshold voltage(constant)
Min: 4,096
Test result value: 10,503
PASS
----
TID:$01 CID:$06
- Rich to Lean sensor threshold voltage(constant)
Min: 4,096
Test result value: 6,404
PASS

The test result above looks great.  It just seems very inconsistent to get for bank 2.  Bank 1 is now solid and passes every time.  Bank 2 toggles between P0431, P2198, and an occasional pass.  

I took some pictures of Bank 2 catalyst.  Here is the view from the upstream side.

and here is the downstream side.

It looks good physically.  No cracks, chunks missing, melting, or soot buildup.  

I also checked it will then infrared thermometer.  I was in the garage so not much load on the engine.  After running (mostly idle) for a few minutes, it was about 400F both upstream and downstream.  I ran the engine at about 2000rpm for a minute and rechecked.  Now both were around 480F.  Not much temperature change across the catalyst in the garage.  This was the surface temperature of the pipe, not the actual catalyst temperature.  

I finally sent the header that kept failing back to Fabspeed to get the catalyst replaced.  Fabspeed was great to work with throughout this whole ordeal.  I installed the header back and have not had the DTCs ever since.  I also checked to confirm that the catalyst monitors did complete and pass.  I moved the car to my Las Vegas home where I needed a smog check to get registration and it passed the smog check as well.