Macster

If this is not a typo/transcription error on your part:

Bank 2
Rear O2 voltage .10 to .8
resistance reading 64
Front O2 voltage .09 - .77
resistance reading 64
Oxygen sensing fluctuated between .99 to 1.02

The rear O2 sensor voltage is wrong. When the voltage drops that is from oxygen in the exhaust gas. The converter should "latch" on to that oxygen, store it, and use it for processing exhaust gases.

(When the CEL comes on in my Boxster and I have the scan tool hooked up and look at the #2 O2 sensor voltages I see some thing similar. The #2 sensor voltage level is fluctuating and I know it should not do this, but remain high (> 0.6 volts).)

As I mentioned in a previous post -- which was from the factory manual -- that if the converter error codes are not accompanied by aging O2 sensor codes -- the converter indicated by the converter error code is bad and should be replaced.

FRUNKenstein

Macster, Quest & dgmark - Thanks very much for the info. This thread turned into a great tutorial on how cats work and diagnosis of problems.

Torontoworker

I had all these issues - had the 'cats are bad' you should change them, etc, etc, etc. Found out you can't clean a MAF if the MAF is BAD.... Change the MAF first - then drive the car for a hundred miles and then reset the codes (if they come back after the MAF change). It is surprising how many codes can be generated by a MAF giving bad info to the ECU. Coolant sensors and air leaks are rare unless like me you had the after market air intake off and didn't get it back on correctly. Oops... And don't buy those ebay cheapo MAF's like I did - lasted one year and then crapped out - buy the OEM part.

Macster

There are always exceptions to the rule but in this case the evidence points to the converters.

MAF problems have their own error codes.

If the OP wants to try this he can disconnect the MAF from the wiring harness and clear the error codes -- to reset the adaptation values -- then drive the car normally for a while (roughly 30 miles) to see if the converter error code comes back.

There is the risk the code won't come back because of the way the car is being driven or because of fueling issues absent the MAF input.

I have driven my my Boxster 275K miles and the last time I cleaned the MAF was back in Feb. 2004 when what proved to be an AOS failure was causing the engine to act up. Oh, the engine had 80K miles on it at that time. The 2nd time the AOS failed I never bothered with the MAF I just had the AOS replaced.

The Turbo has 115K miles on it and I do not know where the MAF is.

Back to the error code... there can be other possible causes, at least for other models. For instance my Turbo P0430 section starts out with making sure the front and rear O2 sensors are not swapped. This is because the two sensors are different. The front one (the #1 sensor) is a wide band sensor while the rear (the #2 sensor) is a narrow band sensor. However, the 996 NA doesn't use wide band sensors.

There is also a check made for proper valve lift operation.

The OP can certainly have this check out performed. IIRC itt takes two techs one to drive the car one to hold the data logger to capture sensor data under test conditions.

There may be other tests/checks. I have a copy of the factory manual but I may not have all the updates/TSBs/whatevers. Only a trained tech with access to all the factory repair information can know what if any other tests/checks there to eliminate the converter and identify what other component or system is responsible for the error code.

questforbalance

Hey DGMark,
I hooked up my Durametric again, but I could not find the fuel trim you mentioned, so I could not get that information. I went into the Engine ECU? Where would I find that? I did rev the engine up to 2,500 rpms, got the cats up above 700 degrees F, checked the o2 sensors and after some funny things with the sensors, like the Bank 2 rear sensor looked like it was following the front sensor for a few seconds, it then followed the same consistent straight line pattern as the Bank 1 rear sensor. Before I started going through the values analysis, I checked on the car's Readiness Status and it said the Converter failed Readiness, but after going through the values analysis, reving the engine, I went back to the readiness status and it said all parameters passed Readiness, INCLUDING the cats. I then went to see if any codes came up and found none. Does this mean this problem fixed itself? This is too strange. I am getting gas today, so I will know tomorrow, which is what usually happens, CEL after filling.

questforbalance

This is something for kcattorney, I was having CEL po43 come up on my car for about 8 to 10 months before I changed the cats. After I went to the Porsche dealership to have it checked out they told me the passenger cat was bad, I looked at my options and tried to clean it first. I took the cat out of the car, removed the o2 sensors and put the cat in a large heavy plastic rubber maid container measuring about 3.5 feet long, 2 feet wide by 10 inches deep, filled the container with 16 gallons of hot water, straight from my hot water heater. I added a quarter cup of detergent, a third cup of dishwashing liquid, and a third cup of citric acid (orange oil). The cat was fully submerged in the water. I then put a clear plastic tube on my air compressor and inserted the tube in the long pipe end of the cat (so it would force water in the opposite direction of exhaust flow) and set the air pressure at 5 psi. When I first started this, some bubbling air came out of both sends of the cat assembly. I think this means the cat was partially clogged. After about 2 hours all the bubbling came out of the opposite end of the cat assembly, so I think it cleared the clog. I covered the container with the cover and some heavy flannel shirts to keep it hot. I ran the compressor for about 5 hours. I then let it soak over night and drained the water and refilled it again, but this time with clear water and ran it for about three hours with the compressor set at 5 psi running and pushing air completely through the cat assembly. After this I rinsed the cat with a few gallons of hot water to make sure I got all the saop out. I then let it dry for a day indoors and put it back in the car. The CEL came on about one day later than it just too. But I was still getting a rattle. The long and short of this is that I think I cleaned the cat, but since the cat was already shot, it would not function properly anymore. The rattle was an indication. My lesson from this is if I ever find out that I have a clogged cat, I will take it out and clean it as mentioned before the inners gets damaged by the back pressure. Good luck kacattorney.

Macster

The converter is not fouled with anything that can be removed with detergent and water.

The potassium component of ZDDP can coat the working surfaces of the converter and reduce its efficiency.

Another failure mode is the converter proper (brick) can come loose and shift out of position and this can affect air flow through the brick and reduce its efficiency.

This can be caused by driving the car with the CEL flashing. This flashing is a sign the converters can be at risk of overheating due to rich misfires and the excess unburned fuel that results when burned in the converters overheats them and can ruin them.

In this case the brick can come loose or just partially melt/collapse.

The converter can wear out. The converter sheds its catalyst metal over time (atoms at a time) and if the converter was on the low end of the coating quality scale this can have the converter simply lose enough of its catalyst metal to reduce its efficiency to the point the error code is generated.

Less common, much less common, is running gasoline with lead in it.

Macster

The intermittent aspect of the error is what I would expect, and have experienced over years with my car. If I watch how I drive -- avoid the more sedate steady state speed cruising -- and keep the RPMs a bit elevated -- mainly by using a lower gear than I would otherwise -- keeping RPMs above 2500 I can keep the CEL away a long time.

But this doesn't alway work. Colder weather seems to bring the CEL more often than warmer weather even though I use the car the same way season to season.

Also, as I mentioned before, discount gasoline seems to affect how readily the CEL appears. Switching from a discount premium gasoline to Shell V-Power cut down on how often the CEL appears considerably. The gasoline doesn't have to be Shell. Chevron works as does Unocal 76 or Philips and there are other name brands but they must be top tier gasolines.

Ahsai

The fuel trims are listed as FRA (long term) and RKAT (short term) under DME. The O2 reading you described means a marginal bank 2 cat. As long as the post-cat sensor reads 0.7v steady most of the time when cruising, the cat is good. The fact that the bank 2 cat follows the pre-cat reding a little before settling down to a steady reading means the cat is marginal.

If you cruise then slow down to a stop w/o applying gas, the post-cat reading should stay at 0 and creeps back up slowly to 0.7v steady at the stop. If it creeps up quickly, it also means the cat is marginal. Best is to plot reading from both banks the same time and it will be clear how they different.

Your car is fine for now as the cat test has passed (will pass smog now). The cat test is performed only from time to time so you may be OK for a while until the next test. Then due to its marginal nature, you may or may not trip the CEL.

Ahsai

BTW, when I said the cat is bad, I meant it's not as efficient as the stock cat, which the DME is programmed to expect. If I remember right, the stock cat is 400 cell so twice as efficient as your 200 cell. So it's difficult to conclude whether your bank2 cat is performed as designed or it's really below its own spec.

dgmark

Ashai hit it on the head, Its not that 200 cell cats are quote bad, they are not as efficient as the stock cats and will trip the cat efficiency codes. My bias is toward the stock cats for this reason in a street car. Every time you clear codes the readiness monitors reset and you have to go through a drive cycle to run them. It looks like you don't have any other issues If you can look at the fuel trims and they are good. The manufactures should be clearer regarding cat efficiency codes and their converters. I have been told by some manufactures that they have never seen this problem and I must be doing something wrong. This just pisses me off.

FRUNKenstein

Thanks Quest!

questforbalance

Thanks Ahsai for the information. And thanks Macster for the information. I know the catalyst brick loosened up in my orinal converter as I used to hear it rattle at times, but when I took it off the brick looked intact. Since putting on the new sport cats, I have not heard any rattles. On another note, I have to give some "customer credit" to Fabspeed because they agreed to replace the cat that is giving me trouble. They have a mechanical engineer who works there who is very knowledgeable and very customer focused. So rather than try to experiment and hope that I do not get any more CELs, I am going to Fabspeed and have the cats changed. Getting CELs in less than two weeks with new cats is definitely a problem. Thanks to all.

questforbalance

Final update: I figured I gave enough time to complain about my Fabspeed cats, and I must give at least a final update to comment on my visit to Fabspeed and the resolution of my problem. Fabspeed agreed to test and repair or replace my cat if I went to their facility at no cost to me. So I took the two hour drive in pouring rain and went to their facility in PA. What a gorgeous facility it was. But what impressed me most was the courtesy and interest in trying to resolve my problem by their people. They inspected my exhaust system, took it apart, tested it and replaced what appeared to be the problem cat. They had us sit in a large waiting area with a huge flat screen tv and fire place. They gave us a tour of their facility. What an impressive facility it was and they had some really cool Porsches and Ferraris there. The long and short of it is, my cat was replaced by Fabspeed at no additional cost and their people were fantastic. I must admit that I was very pleased with them and I no longer have a CEL. What a relief! I can honestly say that I highly recommend Fabspeed for anyone thinking about going with aftermarket cats.

Ahsai

Glad to hear you have it sorted out and kudos to Fabspeed.