Cat clean out questions

[07whitestang]

I live in nys, and want to clean my cats out. I have stock headers and mid pipe, and slp loudmouth catback. Does anyone know of if I can clean my cats out with a chisel or something and install big daddy’s mini cat o2? Does it work? I’d just get a tune, but nowadays it’s hard to get anyone to shut off the rear o2. Thank you

 

[Juice]

Rear O2s are the least of your issues with a cat delete. Your car will run worse over time.

 

[07 Boss]

Rear O2s are the least of your issues with a cat delete. Your car will run worse over time.

How so?

 

[07 Boss]

I live in nys, and want to clean my cats out. I have stock headers and mid pipe, and slp loudmouth catback. Does anyone know of if I can clean my cats out with a chisel or something and install big daddy’s mini cat o2? Does it work? I’d just get a tune, but nowadays it’s hard to get anyone to shut off the rear o2. Thank you

You can use whatever you want to break up the catalytic substrate. Just make sure you get it all out of there or you will be chasing random rattling sounds. I used the big daddy mini cats with a 90* for years without any issues with obd smog testing. I have cats on there now just because my catless mid pipe got a hole and swapped the old one in to get by until I installed the new OR mid pipes, I got the new ones, just been lazy with other projects going on.

I only used the 90* ones due to fitment issues.

 

[JC SSP]

Back in the day I hollowed out many cats for off-road use only A long Piece of rebar or chisel and a hammer worked well.

Today I just buy an off-road H-pipe and your good to go. FYI I am living in the FREE state of Florida. No emissions testing. Lol

 

[86GT351]

Back in the day I hollowed out many cats for off-road use only A long Piece of rebar or chisel and a hammer worked well.

Today I just buy an off-road H-pipe and your good to go. FYI I am living in the FREE state of Florida. No emissions testing. Lol

No emission is nice. Would be nice if they would switch to a safety inspection though. You would be surprised at some of the junk that comes through ere. mainly older cars with safety recalls that we are obligated to fix. Of course when you tell them there brakes are metal to metal or there tires are conceivably worn out, there is no interest in repairing. As state inspection eliminates alot of the cars on the road that should not be there.

 

[cavero]

Before you do anything permanent, double check what NYS checks when they hook up their scanner. VA will make sure all of the O2 sensors are turned on, or they'll fail the car. My shop had turned off my rear O2 sensors so the car wouldn't trip codes since my hi flow cats weren't actually doing much. At the time it was legal, but then VA changed their rules and we found out the hard way.

With the way NYS is about the environment, I would be surprised if they're more lenient than Virginia (or at least the counties in northern VA that do emissions)

 

[Juice]

NY has adopted CA 50 state emissions. Good luck getting smogged.
Ps: PA just tightened their noose on smog.

 

[Juice]

How so?

Ask your tuner. But rear O2s do a little more than monitor cats.

 

[07 Boss]

Ask your tuner. But rear O2s do a little more than monitor cats.

Yes the rear O2 sensors are used to recalibrate the fronts as they tend to "drift" over time. But you don't need cats to do that. We're talking about deleting the cats not the sensors.

 

[Midlife Crises]

I have run this same vehicle in multiple configurations without cats. Early on (pre supercharger) I had tunes with the rear O2 sensors working and tunes for the same configuration with the O2s off. At that mild level of bolt on bliss there was little or no difference in performance. The exhaust smelled different when the cats were on or off. Today, at a much higher performance level catalytic converters do have an effect on tuning and performance. When I replaced a Kooks cated X pipe with an uncated X pipe I lost just over 1psi from my boost gauge. That means I hade back pressure and back pressure is bad.
Now it is tuned with the rear O2s turned off and runs pretty good but on hiway fuel the exhaust smells just awful. Race fuel smells better.

 

[Juice]

Yes the rear O2 sensors are used to recalibrate the fronts as they tend to "drift" over time. But you don't need cats to do that. We're talking about deleting the cats not the sensors.

I've come to the conclusion, based on Ford's emissions system operation doc, that is not the case. Not sure about the narrow band O2s and drifting cal. But the WB upstreams are not calibrated using the rear O2s. The WB O2s have a reference chamber of clean air. This cthamber gets replenished during a coasting fuel shutoff event. Rear O2s do not come into play.
Anyway, not going to get into an advanced tuming discussion here

 

[JC SSP]

Interesting, I always thought the rear O2 were only for checking catylist function and did not impact engine performance. Would like some of the members with tuning experience to confirm.

 

[07 Boss]

When I replaced a Kooks cated X pipe with an uncated X pipe I lost just over 1psi from my boost gauge. That means I hade back pressure and back pressure is bad.

Actually if you perform a mod on your car and the boost drops that means you're making more power and have less backpressure. Boost is a measure of resistance meaning that is the air backing up and not getting into your cylinders. Now if your boost pressure drops that means more air is getting into the cylinder and thus more fuel is getting burned making more power. You're still pumping the same amount of air but less is backing up. That's good and makes more power. If you add cams to an SC set up the boost will drop and you will make more power.

Interesting, I always thought the rear O2 were only for checking catylist function and did not impact engine performance. Would like some of the members with tuning experience to confirm.

I do mess around with my HP Tuner set up a bit and this is my understanding on how it works. The front sensor signal tends to migrate or shift over time, meaning it is not as accurate. So every once in a while the computer looks at the rear sensors and sees when it is at stoich and uses that to recalibrate the stoich for the front sensors. I also believe you can adjust for this in he tune or just change out your front sensors at some time interval. I have no clue how far out of calibration an O2 sensor can get so I'm not sure how critical it is. I know I ran for years with the rear sensors turned off and beat my car like a red headed step child without any issues.

Here is an interesting note though. When our cars were manufactured there were two separate part numbers for the front and rear sensors and now when you go in there is only one that is used for both. When I was having some issues my tuner suggested I go back to using two different sensors. I think I got these from NGK but they are definitely two different part numbers. I haven't had issues since switching them from the bosch ones I had in there.

 

[GlassTop09]

Interesting, I always thought the rear O2 were only for checking catylist function and did not impact engine performance. Would like some of the members with tuning experience to confirm.

With Spanish Oaks ECU's (05-10 S197 MY's), the rear O2 sensors only function is to read the O2% in exhaust post-cat to inform the ECU on catalyst function\efficiency performance so that the ECU can then make any needed front O2 sensor amplitude switching changes to ensure the cats get the right amount of free O2% after any NOx reduction done in front cat substrate (separating O2 from N2.....what cerium does in an OBDII TWC cat....it retains\holds the freed O2 to be used to oxidize any excess HC or CO in exhaust) to properly\fully oxidize any excess HC or CO in exhaust so that no free O2% is read by the rear O2 sensors post-cat (how ECU determines catalyst efficiency% by counting the number\frequency of the rear post-cat O2 sensor's rich to lean switches vs the number\frequency of front pre-cat O2 sensor's rich to lean switches.......a good cat will show very few to no rich to lean switch counts vs the front O2 sensor's rich to lean switch counts).

Refer to this thread here: https://www.s197forum.com/threads/lunati-voodoo-21270700-camshafts.136257/page-17 post #322
Also, can read up here: https://iihs.net/fsm/?d=7&f=Catalyst Efficiency Monitor.pdf

Hope this helps you out.

Yes the rear O2 sensors are used to recalibrate the fronts as they tend to "drift" over time. But you don't need cats to do that. We're talking about deleting the cats not the sensors.

This feature Ford incorporated into the S197 Mustang's w\ the advent of the Coyote\Copperhead ECU's starting in the 2011 MY forward........not in earlier MY S197 Mustang ECU's. This is called FAOSC (Fore\Aft Oxygen Sensor Control) which does exactly what you've described & 1 of the features that Juice is referring to when he says that the rear O2 sensors do more than just catalyst monitoring.

Can provide a picture of this feature\setting existing in a 2011 MY S197 Copperhead OS tune calibration if warranted...........also can provide a picture of most any 05-10 MY S197 Spanish Oaks OS tune calibration showing this FAOSC setting doesn't exist as well if warranted..............

My 2 cents FWIW.......................

 

[Juice]

You may not have FAOSC exposed in SO pcm, but it has it based on this:

https://www.fordtechservice.dealerconnection.com/vdirs/diagnostics/pdf/OBDSM804.pdf

 

[Autokyrios]

Just my $0.02 and this is one of those topics but...No point to removing modern cats. On older cars, sure, some, but on these? Not worth it.

If you're doing a lot of aggressive mods that change the airflow (pressure) having or not having cats isn't the issue. (It's a bit like changing the intake requirement and seeing a difference with or without the stock air filter in...the presence of a filter isn't the issue, it's the wrong filter/intake for the job.)

On a stock or normally-modified engine, the car won't do any noticeable difference better and will have problems as the readings will be wrong. 02 sensors help the computer understand how the combustion is doing. If you tune it to compensate, still not worth it. You can fiddle with the tuning to calm things down, but that's not getting you a gain.

Only normalcy in not having cats is basically full-time race cars, and that's a different reason entirely. The whole "delete your cats and you'll make more power" thing is just noise.

The 05-10 Mustangs came with decent cats. This is an area where manufacturers work on their fuel efficiency numbers, so they're not going to put things in that tank the car.
You'll only have an issue if they're bad, and it takes quite a while for a cat to go bad normally (unless you don't take care of it). Best all around approach if you actually do have a bad cat, or upgrade your exhaust, is to replace with 'high-flow' cats (which even then is kind of a meh-increase) and you'll be good.

 

[07whitestang]

Update: I ended up dropping my mid pipe, cutting the fronts of the cats off, gutting em, welded them back up. Bdg cel eliminators are at the post office as I type this. I will let you know how it goes.

 

[07whitestang]

Update: I installed the bdg cel eliminators, have drove my car over 400 miles and no light. Only thing I would recommend is that when installing them with stock exhaust, get the 90 for it. Without it is a very tight fit. Thank you everyone