CEL is back...PO421, and PO431 “warm up catalyst efficiency blah blah blah”

Ptech believes that both primary cats are failing. Just replaced the downstream Bank 2 O2 sensor to clear the previous CEL, and now this.

OEM cats are $1400 each.

eBay has two sellers of aftermarket cats, made by Davico, and the other by Calnorth. Both are priced at approximately $450 a side.

Anyone has experience with these aftermarket cats?

Anyone got a set of primary cats for a 4.8L GTS, or S laying around?

 

I wonder if a muffler shop could take the sections of the secondary cats and put them into the primary cats (cutting & welding), or if the shape and size of that section is different. There should be some secondary cats laying around from those who are running the bypass pipes.

 

I’ve got the V-6 and am going through a similar scenario now. I had an audible exhaust leak and took it to a local muffler shop hoping it would be a simple weld repair, as the dealership wanted over $3000 to fix it.

The tech stated he could pull out the affected section, cut out the bad flex pipe and replace. However, he said the labor involved to do the pull, put everything back in place, tack weld it, re-pull it for final welding, then replace it all again would likely be more in labor than just replacing the entire section involving the primary cats. He also added that at this point, the cats could go bad and end up requiring replacement down the road, so it would probably be better to replace the cats now.

The dealer wanted $1800 for the Y-section with the cats, they would need to come from Germany, and they were on back order and would take 4-6 weeks to get.

I searched online and found an aftermarket part from carparts(dot)com for under $300, plus shipping. He is installing it now, so will see if they are any good.

Not sure if your model has a similar availability problem.

 

This is a bad time to be shopping for CATs, Palladium is through the roof. I took a peek at Magnaflow CARB certified...yikes. 1400 a side for the secondary, direct bolt-in primary coming soon. Walker is much more affordable, sold at Advanced Auto, weld in universal CARB compliant front cats for the CTT are $522 each, rears are $623. Years ago I swapped in two CARB compliant Walker cats in the old 2000 Audi A8 for $130 each. Good as new. I also spotted some universal Walker CATS (Not CARB) for your 09 GTS in the $130- 170 range on Advance Auto. You might want to talk to a local muffler shop to see if they can help you without breaking the bank.

Cats should last a very long time. Things that kill them include, infrequent use or lots of short trips that don't get them up to temperature, bashing them on rocks or curbs, etc., overheating them or coating them with oil. That last one you can definitely do something about. Maintain your PCV system, and - never a fan of snake oil, I'd make the exception here - add some kind of cat cleaner to your fuel. The Turbos are thirsty and beat up the PCV system, but I've yet to meet the German car that didn't have a bad oil habit...looking at you dearly departed D2 Audi A8. So, if you open your oil fill cap at idle and go to place it back on, do you get some decent suction? If yes, PCV diaphragm is likely torn, and the engine is sucking in far too much blow by gasses and oil vapor. The PCV on the 955 Turbo is serviceable, pop the cap, replace the diaphragm, spring and cap, and you are good to go. I believe yours is integrated into the cam cover. Not sure if it is serviceable.

Are your air injection pumps working OK? They are the two gizmos on the top at the back of each cylinder bank. Their job is to blow air on the CATs at start up to light them up quicker, like you would blow on twigs to help a camp fire. You can test fire those if you've got the software. VAG Com lets me do it on my 04, not sure about the 957. If either of these are dead, that will hamper CAT performance.

Good luck,

Brian C.

 

Good info info in this post, though not all German cars eat oil. My supercharged 997 with 60k miles on it uses only 1/2 qt every 4,000 miles. My regular 997 uses the same, but every 5,000 miles, and my modified Cayenne Turbo S uses virtually zero oil between 5,000 mile changes.

The other thing that effects cat life is some fuel additives and also unusually high Zinc and Phosphorous (ZDDP) in the motor oil. That's a bit of a tradeoff as this is great for the engine, but less great for the cats. Oils with 1,000 - 1,200 ppm Zinc & Phosphorous should be fine for the cats. Oils with less than 1,000 aren't really good for engine wear. If the formulation has Moly in it too, that's helpful as an anti-wear additive.

 

I missed ZDDP Conversations :-)

 

go to any air cooled forum, and ask what oil to use. Your wish will come true.

 

On my 08 GTS, the Porsche dealer that sold it to me 3 years ago had put in aftermarket primary cat on the driver's side. No, it was not OEM - turns out, even Porsche dealers don't like paying Porsche prices, so the Porsche dealer used car sales dept (which is apparently a separate legal entity from the parts dept at most dealerships) had an outside indy shop perform the repair before the car was sold by the dealer. The O2 sensor they replaced along with the cat has failed and I replaced it with a Denso sensor (which turned out to be a repackaged Bosch...), but the cat is still fine. Judging by the fact that the O2 sensor was the cheapest garbage they could find, the cat is the same. Yet, still chugging along.

That OEM cat used to be ~$900 and even less before that. I was ready to order one 2 years ago at $900 just because I did not trust the aftermarket one. I sat on that thought for a while and when I finally went to order it, new year 2020 rolled in and the price hiked up to $1400. I said hell no, I'll put in 5 aftermarket cats before I pay that. Besides, the OEM cats don't seem to be that great, lots of posts on the forum about them failing. Whereas the original cat in my 96 Toyota with 240k on the clock is still ticking.

The Davico one is $300 + tax + shipping on Rockauto.com. Check them out. There's also a 5% off coupon around for RA.

Hope this helps!

 

Here's a DIY video on a 955...

 

my flex sections were bad on both sides. Engine was coming out for work so i replaced the downpipes with Catless FVD while engine was out. Got spacers with mini cats inside of them for the O2 sensors. I still have the secondary in place as not to be a complete ***.
Both pipes were price of one OEM

 

Awaken zombie thread... OP pinged me for part no.s on non oem carb approved options. I haven't been on the site in ages. OK, here is what I found, none of it great. Walker doesn't seem to have a reasonable replacement. Both MillerCat and MagnaFlow make replacements. https://www.carbcats.com/?engine_siz...pe=show%20all#

MillerCat also makes a nice flex pipe repair section so you don't have to replace the whole front cat assembly: https://www.millercat.com/cayenne

And finally, here is a link to the CARB searchable database of approved replacement CATS: https://ssl.arb.ca.gov/AftermarketParts/catalysts

As for the universal approved front cat I mentioned by Walker at Advanced Auto, it no longer lists, but the MagnaFlow one does for $562 per side. and that's still a universal, so some assembly required (cut & weld). https://shop.advanceautoparts.com/p/...source=certona

Hope this helps someone. And don't forget, with the Turbos, change the torn diaphragm in your PCV and the check valves (FCP euro has them for reasonable money) to ensure you are not sucking in and burning excess oil vapor which is fouling up your cats. If they are in bad nick, repair them and then run some cat cleaning miracle in a can and be surprised when your cats come back to life. I was, about two years back.

Regards,

Brian C.

 

Could anyone elaborate here? Should we be doing this proactively? How can we tell if we should? Which parts specifically? Thanks!

 

If you've got a turbo or even an N/A and are consuming excess oil, here is the very first place I would check:

PCV replacement Cover, spring & membrane $35. I bought mine on Amazon, but that listing is no longer active. Here is an equivalent on E-bay, and it is a damn sight cheaper than the $820 FCP would charge you for a new cam cover assembly for an '04TT. At just over 100k miles, my membrane was torn at the perimeter.

And here are the check valves that prevent boost pressure in the intake manifold from overwhelming the PCV for $80. Normally aspirated engines don't need it because they never have high (boost) pressure in the intake manifold. Porsche Engine Crankcase Breather Check Valve

Ever since changing these out,, my oil consumption is essentially nil between oil changes. And did I mention being unable to pass emissions due to oil-fouled cats? That happened, then I dug these up, ran some miracle in a can cat cleaner and fine ever since. Absent overheating them or bashing them off-road, cats should last the life of the vehicle. If you ever have to change yours, find the "Why" or you'll be doing it again.

Oh yeah, props to DIY Dan for his excellent series of videos covering lot's of Cayene usual maintenance and fixes, including the AOS membrane replacement:

 

I bought these and I'll be damned if I can tell the difference between them and the factory cats I replaced. Had a cracked flex pipe and Porsche quoted me over $3000 for the parts.

https://www.ebay.com/itm/353292062022