I have Magnaflow highflow x-pipe. After about 9000 miles I get the 0420 ineffeciency code. My guy tells me it's because the highflow cat can't keep up with the exhaust and the 10% ethanol will effect it. Question, why are the O2 sensors in the middle of the cat versus after the cat? I just noticed it when I had the cats looked at. It would make more sense to place the O2 sensor after the cat so that the exhaust is read "after" it goes through the entire cat versus 1/2 the cat. This make any sense? We plugged the hole and placed bungs after the cat for the O2's to see if that helps.

thoughts?

 

Not sure, but in for answer...my Mangaflow catted X-pipe is arriving on Thursday!

 

I have the bassani catted x which has the rear o2's behind the cats. This past weekend I received the same code.

My guess is that the factory threshold is pretty tight.

I simply cleared the DTC, hasn't come back yet.

It took about 4000 miles for it to come on.

 

My thoughts too on the factory threshold. I had them on my 99 Cobra, 2001 GT, 2002 Gt, and now 2009 GT. Odd this is my 4th Mustang yet 1st issue.

 

Gotta remember that teh S197 is a complete redesign. The onboard electronics are quite a bit more sophisticated than your previous mustangs. Which, although different were based on the same architecture and electronics.

 

My SLP catted X-pipe has the O2 sensors after the cats. I killed my factory cats after running too big of injectors (not tuned correctly) and was throwing the same 0420 codes. I would clear the codes only to have them pop up a few days later. After a couple months the factory cats started rattling and plugged up. Hopefully, you aren't on your way to killing your aftermarket cats? Is it possible that your car is running overly rich, or the MAF & injectors aren't matched up?

 

As far as running rich I don't believe so. The Diablo came with the "canned" Steeda 91 Octane tune that I loaded. The light hasn't been back on in two weeks.

Thanks for the replies,

 

Bump for future updates & other people's encounters w/ this issue...

 

Its EPA requirement to have the o2 placed in the middle of the cat. If you have a high flow cat then it shouldn't matter if it can keep up with the flow or not. make sure the connector is plugged in properly and the pins are making full contact.

 

Update, just lit a P0430 tonight after about 1700 miles, lol

Cleared it with my SCT when I arrived at my destination. No big deal.

ยท P0430 Catalyst System Efficiency Below Threshold (Bank 2)

 

The code means you have probably melted the cat. Got the same code on a roush p-51 which had the stock cats. When we took the cats off the car the actual catalyst came out in pieces. This happens when you run too rich.