Quick summary: Car is an 06' Vantage V8. Severn Stage 1 tune, quicksilver racing exhaust. Got a CEL Code P0420 (CAT efficiency Bank 1 low). Took to mechanic who did extensive testing and determined the O2 sensors were good and the CATs are going bad. Decided to double check it wasn't the sensors, so replaced rear O2 sensors (forward O2 sensors had already been replaced by previous owner and were relatively new). CEL came back, same code so determined it was in fact the CATs. New CATs are $6500-$7000 with shipping. I said screw that and ordered brand new 200 CEL hi flow CATs. Put them on, drove them for a bit (holy lord is it LOUD, ugh), got CEL, but this time it's both banks (P0420 AND P0430). My assumption is with the hi flow CATs the system is determining that too much exhaust is getting through and throwing the code? Does the ECU need to adapt? Will it eventually go away? I've spent $2500 so far trying to fix this and now I've got a really loud car with a CEL. Any advice is appreciated.

 

Additional information. The car has always and continues to run absolutely perfect! Literally never has sputtered ever and runs VERY strong!

 

Can you revert back to the stock tune to test the new catalyst? Basic canned tunes like to add fuel for power. Are you trying to pass an emissions check or eliminate the CEL?

 

I think I have an answer to the problem. Just trying to get rid of the CEL. I don't have to smog the car for 18 months so I'll cross that bridge down the road.......

 

Good to hear that, let us know of your progress.

 

The Hi Flows are too freakin loud.......I thought I could live with it, but the car sounds like a full NASCAR race car with the Hi Flow CATs and the Quicksilver racing exhaust. The OEM CATs visually look like they are in great shape. Zero damage to the honeycomb on the inside of either CAT. I've read that a deep clean with detergent and power wash might be an option to essentially dislodge anything inside the CAT. Does anyone have experience with this? I could put an O2 sensor extender on the OEM CATs to get rid of the CEL. The ONLY concern I have is if in fact the CATs are damaged and any part of the honeycomb comes off and gets ingested into the motor then the motor is destroyed.........but visually the honeycomb looks perfect.

 

But I am more and more getting to the point where I'm gonna just spend the $7k and get brand new OEM CATs..........ugh

 

I replaced my cats for 200 cell hi-flow and got the emissions message with the 420 & 430 codes. That means that the threshold from the front sensors to the rear has been exceeded. That would be an indication of the cats not doing their job, hence the error pops up on the code reader with hi-flow cats. I tried spacers on the rear sensors but still got them once in a while. I also got a Stage 1 tune, and I got the tuner to suppress the code from a new file. I assume they do it by raising the threshold, but I am not sure. So far so good. I am in CA where the smog ***** now check if there is a modified file on the ECU and will not pass it. But I am in a location that does not require smog checks every 2 years so I don't care. When (if) I sell the car, I will throw the OEM cats and the original file back in and all should hopefully be good.

Regarding the noise, I too thought it was too loud, but I have the OEM exhaust with a remote switcher. With the valves closed they are just right, but when they are open watch out. I mostly keep them closed but open them on long stretches when canyon carving. The sound is divine.

 

i would undo whatever it is that's been done and see if that fixes the problem before throwing seven grand at it with a wish and a prayer that that will fix it.

but then again, i'm the kind of guy that would never have done whatever has been done to the car in the first place. so my advice is very biased. good luck!

 

Might want to get a second opinion on those cats.

 

You could install and X pipe, that would quiet it down quite a bit.

 

See if you can find some used stock cats before you drop 7k on oem cats.

 

I fixed this on my car with mini-cat bung extension so post catalytic sensor sits behind a dense (albeit very small) cat element that's not in the path of the exhaust flow. Makes the exhaust gas proper for the sensor and avoids DTC codes. Works like a charm

There's many to choose from.

Look up prosport mini cat o2 for an example

 

SemiF19 -

With regards to the exhaust being louder than you would like, have you verified that the exhaust valves are not stuck in the open position. I remember reading that if fuse 22 is pulled to keep the valves open, that the valves may eventually seize in the open position and not close. If I remember correctly, the valves (at least on the 4.7) can be seen from behind the rear wheels on either side of the back box and you can move the plunger which will move the valve itself. If you discover that the valves are in fact stuck open and you can manually close them and the exhaust note is acceptable, you could simply repair or replace the actuators and get a remote exhaust valve actuator.

Just a thought and I hope you get the issue sorted.

Also, please note that I know just enough to be dangerous and the above could be completely wrong.

 

I've done a number of tunes with either catless pipes, headers or aftermarket CATS, that would leave a CEL (p0420 and P0430). I've "tuned out" the back O2 sensors and what the tuner does is redirect the ECU to no longer report the threshold failure even though the ECU still does its checking periodically (every 50/100 miles depending on that mfgr's EMS).

It's a simple "box uncheck" in the tune through a hack software. This is the one I use and what I do. BTW, you have to do it this way to preserve the startup diagnostics where the rear O2 sensors are checked as "present" and accepting and returning a voltage. Some mfgrs don't do a startup diag, most do.

ENGINE DIAGNOSTICS > DTCs > Uncheck boxes @ P0420 and P0430 (Note, even the hack SW now warns about modifying data tables BC the EPA is on a warpath now).




Also, this DEFINITELY will be caught now in a CA emissions check as since July 2021 they now check for a factory CVN that gets changed when the data tables are accessed and modified. The only way around it is if the tune (tuner) has submitted and received a CARB certification that delivers a CVN California will now accept. Some tune houses (very few) have submitted and received a CARB cert. Rumor has it CO now uses this check too but I cannot confirm that. This will only get more used, not less.

Here is an example of a failed CA emissions report BC of a tune: