P0430 Code and Brown Exaust Smoke

I’ve searched the the threads and haven’t found any solid hints.

The car idles fine, runs fine until I smash the pedal and take it above 4K, then I get a decent cloud of brown smoke out the exhaust and a CEL of P0430. “Catalytic efficiency below threshold bank 2” is what it displays, and there are a butt-load of things that that could mean.

Any clues on where to start?

‘11 GT500
‘14 2.3 w/2.4” pulley
56# injectors
66mm TB

Everything else is stock.

Any advice is appreciated.

Dark smoke is fuel

Stock cats still on the car?

Zemedici said:

Dark smoke is fuel

Stock cats still on the car?

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Stock cats are still on it. The smoke is a dark brown and some black in it. The car has 80k miles on it.

Car drive any different?

Zemedici said:

Car drive any different?

Click to expand...

Not at all. The coolant level is the same, idles fine, drives fine, it’s just a big brown cloud when I get on it hard in the first 3 gears.
Gas mileage went to shit. From mid 19’s to barely 16, driving easy.

Did this start after installing those mods or have they been on the car for a while now? Still stock tune as well?

I'd datalog it and see if one side is running richer than the other. You may have a bad or leaking injector.

Well based on the code and fuel mileage, I would suspect a plugged cat.

You usually have a severe loss of power complaint, but I've never dealt with this on a blown car so maybe it just over powers it.

Catmonkey said:

I'd datalog it and see if one side is running richer than the other. You may have a bad or leaking injector.

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I'd expect to see a rich O2 code for that bank. I've been out of the game for quite some time but when you have a code about that cats like this, its the downstream o2 sensor not seeing what it is supposed to from the cat

The blower, mods and a TASCA tune was done when it had 8k miles on it, it now has 80k. I haven’t made any changes to it since then. There’s been no power loss at, and this all started 4 days ago.

Now to study up on data logging with a SCT x3.

Have you changed the O2 sensors with that much mileage?

How old are the plugs? How many miles on them?

70k miles since I’ve changed the plugs and it’s the original O2 sensors.

I’ll start with thorough tune-up and see how it goes.

I would be looking at a bad catalytic converter on the drivers side.

From the 2014 Mustang Service Manual

P0430 - Catalyst System Efficiency Below Threshold (Bank 2).pdf

That doesn’t sound like it is going to be inexpensive to replace either.

An opportunity for Kook’s and a catted h-pipe if that’s the verdict. A stock replacement is $1k

Would a 170° thermostat and 40° weather have anything to do with this issue? I forgot about putting that in 20k miles ago.

You can find spare OEM cats - I still have mine in the garage but kinda far from you.

I finally found the time to drop the H-pipe, low and behold the culprit. What would cause a cat to come apart like that? Nothing looks melted. I pulled the spark plugs and they don’t look hateful besides that the gap had grown to .036.

Now to figure out if I want to slap a JBA 3” catted H-pipe, pony up for an OEM one, or shoot for the moon and go long tubes knowing that I’m putting them on with the car on jack stands.


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A boosted, aggressive tune would do that. I read brown smoke and I figured the cats were blowing out. Even with Ford spec'ing very high quality and durable stuff for their production cars, a restriction in the exhaust that gets hot will only last for so long.

Just a bit of fair warning, the high flow cats used on header systems tend to do this too. I believe there is a brand of cats made for header systems that are much more robust, but I cant remember it off the top of my head.

@My Monster found them:

http://vibrantperformance.com/catalog/index.php?cPath=1527_1326

They arent cheap, but should last at the rated power level.

They lasted 70k miles with the 2.3 TVS and a 2.4" pulley, I am impressed that they lasted that long. The passenger's side is still in one piece. I think I'd rather swap out H-pipes than swap in headers, it's a damn tight fit under there.