How common is it to burn a cat?

[vladniko86]

I drive my 86 pretty hard. For about 6 months now, if I start it and let it sit in one place I smell a mixture of sulfur and gas in the cabin. Once I start driving I can’t smell it, but if I sit at a light for a while I can. How can I check for a bad cat? Also, I feel like I shouldn’t buy another oem headers assembly with cat for like $200 off a parts puller because I’ll kill it anyway. But if I get catless, I’ll need to drop $400 on headers and $800 on tuning software. Kinda pointless imo because I don’t know if that tuning software will work when I go to engine swap it. Thoughts?

[86MLR]

Have you lost performance?

Have you thrown a code?

Could it be just an exhaust leak?

You don't "need" a tune for a decat, you just wont see the performance gains that you "can" get with a decat and tune.

If your front cat has collapsed you can just remove the header and front pipe, punch out the cat in the header to remove the cat honeycomb stuff and the white lagging, inspect and clean the front pipe if required (bits of the front cat), reinstall everything with new gaskets and, abracadabra, fixed for the cost of a few gaskets.

No tuning required.

[vladniko86]

Originally Posted by 86MLR

Have you lost performance?

Have you thrown a code?

Could it be just an exhaust leak?

You don't "need" a tune for a decat, you just wont see the performance gains that you "can" get with a decat and tune.

If your front cat has collapsed you can just remove the header and front pipe, punch out the cat in the header to remove the cat honeycomb stuff and the white lagging, inspect and clean the front pipe if required (bits of the front cat), reinstall everything with new gaskets and, abracadabra, fixed for the cost of a few gaskets.

No tuning required.

I was getting P2096 for the longest time ever. I changed both O2 sensors to make sure that wasn’t it. I would do that but wouldn’t I need spacers to prevent code? Also would I need to cut it and reweld to get to the cat? Seems like there isn’t direct access


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[vladniko86]

Also I don’t think it’s an exhaust leak and I honestly don’t remember about performance it seems the same. I have a muffler delete in the back and when I did that I tested all connection spots and didn’t see any leaks


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[86MLR]

You can use a "minicat" and extention to fool the ECU, I used one for a year or so prior to tuning with no issues.

No cutting or welding needed.

Pics: This is my old 2017 header that I punched out, which actually outperformed a Tomei UEL I bought during a late night impulse buy.

If your staying NA for a daily driver, decatting the OEM header makes more sense than spending money for a sound or no real gains, after a tune my 86 made 198hp atw with a fully decatted OEM exhaust.

Plus it will pass any visual inspection and you have no issues with heat as the OEM heat sheilding is still in place.

Opinions may vary

[86MLR]

Stop at step 5

The one on the vid seems to he a metal cat, the ceramic? OEM cat smashes apart much easier.

Just remember there is that white lagging material as well you need to get out.

There will be a slight increase in noise at cold start, typical to any catless EL header, but no where near as loud and obnoxious as a UEL header at cold start.

[Ultramaroon]

I've never had an oxygen sensor fail shorted. They fail open which causes a rich condition. I think you've just had an exhaust leak all along.


Blaming it on a cat makes no sense.

[Stomachbuzz]

Originally Posted by 86MLR

Have you lost performance?

Have you thrown a code?

Could it be just an exhaust leak?

These are good points - a burned cat will have some symptoms. There is a CEL for catalytic converter performance below threshold - the dreaded P0420

Originally Posted by 86MLR

You don't "need" a tune for a decat, you just wont see the performance gains that you "can" get with a decat and tune.

If your front cat has collapsed you can just remove the header and front pipe, punch out the cat in the header to remove the cat honeycomb stuff and the white lagging, inspect and clean the front pipe if required (bits of the front cat), reinstall everything with new gaskets and, abracadabra, fixed for the cost of a few gaskets.

No tuning required.

This is where I suggest you take this 86MLR's replies with a grain of salt.

"You don't 'need' a tune for a decat"
Well...ya kinda do.
If you don't tune, the car will throw a CEL for catalytic converter issues. The car has a pre-cat and post-cat O2 sensor for the specific purpose of monitoring the condition of the cat. In the USDM market at least, I don't know about AUS
Usually will not cause the computer to retard performance, but will make you fail inspections/emissions and leave your ignorant if other issues pop up.
Additionally, if you don't tune it, it doesn't make sense to do...

If you do mess around with "punching out the cat", be careful. These are heavy metals and toxic that the cat is made up of. That's why catalytic converters are so expensive when new, and worth so much used. People out here using a sawzall, stealing cats in the middle of the night for the scrap value of the precious metals.

definitely need thick gloves and a mask at the very least -- for 'punching out the cat' not stealing them!

Originally Posted by 86MLR

You can use a "minicat" and extention to fool the ECU, I used one for a year or so prior to tuning with no issues.

No cutting or welding needed.

Pics: This is my old 2017 header that I punched out, which actually outperformed a Tomei UEL I bought during a late night impulse buy.

If your staying NA for a daily driver, decatting the OEM header makes more sense than spending money for a sound or no real gains, after a tune my 86 made 198hp atw with a fully decatted OEM exhaust.

Plus it will pass any visual inspection and you have no issues with heat as the OEM heat sheilding is still in place.

Opinions may vary

Again - grain of salt.
"198hp at the wheel"

Originally Posted by Ultramaroon

I've never had an oxygen sensor fail shorted. They fail open which causes a rich condition. I think you've just had an exhaust leak all along.


Blaming it on a cat makes no sense.

I've found this to be true in my experience as well. Any issue that was actually fixed with a new O2 sensor (vs throwing an O2 sensor at the issue, when it was actually something else causing it) was a very rich condition. Like, 'getting 6mpg and choking on the gasoline fumes at a red light' rich.

Usually pretty well diagnosed via OBD though.


To OP,
The sulfur comment is somewhat specific to a bad cat. I don't think I've ever experienced it myself, but I've often heard of "rotten eggs" when people talk about their cat going bad.
A few different ways to check for a bad cat - the CELs via the OBD would be the easiest and most direct.
Other ways are to test physically. A good cat will get very hot, a bad cat will not. Using an Infrared thermometer to measure the exhaust temperature. The pipe right before the cat will be like 250F, and the cat should spike to like 700F. A bad cat will be like 325F.

If you need a replacement cat on a budget, I would absolutely scoop one off craigslist. People trying to give these things away for like $100 with barely any miles.
It's a no brainer.

If you want the performance option, then do that.

It is possible that running rich or lean prematurely destroyed the cat. Might need further diagnosis.

[86MLR]

Originally Posted by Stomachbuzz

This is where I suggest you take this 86MLR's replies with a grain of salt.


Again - grain of salt.
"198hp at the wheel"

BS you say....

What is so hard to fathom about 198hp (145kw), with a Ecutek and a tuner who actually know what they are doing.

Plenty of people have been getting typical numbers, not with flash tunes though, real tunes using real tuners, search around if you don't believe me.

NA the only real restriction is the 2 cats.

The OEM airbox is not a restriction either.

Full decat, snorkel mod, Mishimoto intake tube, OEM tune saw 115kwatw, full tune saw 148kwatw.

Fuel: 98RON

As for throwing codes, people have been using extensions to fool the ECU for years, add a mini cat and your good to go, it's not rocket science.

Check my build thread for my journey with modifying my 86, parts I used, parts I binned, money I've wasted.

http://www.ft86club.com/forums/showthread.php?t=133311

In saying this, the best performance gain was from using one of the best Ecutek tuners who specializes in Subaru WRX STI and Mitsubishi EVO's.

https://pulseracing.com.au/

Have a look on their facebook page, some nice cars and some funny shit, and if your into WTAC some cars and people you may know.

Now I'm curious, what testing and tuning have you done to say my results are BS, I'm always open to a educated critique based of testing and sound engineering principles.

Link your build thread, post up your results

And go........

Opinions may vary

[vladniko86]

Originally Posted by Stomachbuzz

These are good points - a burned cat will have some symptoms. There is a CEL for catalytic converter performance below threshold - the dreaded P0420





This is where I suggest you take this 86MLR's replies with a grain of salt.



"You don't 'need' a tune for a decat"

Well...ya kinda do.

If you don't tune, the car will throw a CEL for catalytic converter issues. The car has a pre-cat and post-cat O2 sensor for the specific purpose of monitoring the condition of the cat. In the USDM market at least, I don't know about AUS

Usually will not cause the computer to retard performance, but will make you fail inspections/emissions and leave your ignorant if other issues pop up.

Additionally, if you don't tune it, it doesn't make sense to do...



If you do mess around with "punching out the cat", be careful. These are heavy metals and toxic that the cat is made up of. That's why catalytic converters are so expensive when new, and worth so much used. People out here using a sawzall, stealing cats in the middle of the night for the scrap value of the precious metals.



definitely need thick gloves and a mask at the very least -- for 'punching out the cat' not stealing them!





Again - grain of salt.

"198hp at the wheel"







I've found this to be true in my experience as well. Any issue that was actually fixed with a new O2 sensor (vs throwing an O2 sensor at the issue, when it was actually something else causing it) was a very rich condition. Like, 'getting 6mpg and choking on the gasoline fumes at a red light' rich.



Usually pretty well diagnosed via OBD though.





To OP,

The sulfur comment is somewhat specific to a bad cat. I don't think I've ever experienced it myself, but I've often heard of "rotten eggs" when people talk about their cat going bad.

A few different ways to check for a bad cat - the CELs via the OBD would be the easiest and most direct.

Other ways are to test physically. A good cat will get very hot, a bad cat will not. Using an Infrared thermometer to measure the exhaust temperature. The pipe right before the cat will be like 250F, and the cat should spike to like 700F. A bad cat will be like 325F.



If you need a replacement cat on a budget, I would absolutely scoop one off craigslist. People trying to give these things away for like $100 with barely any miles.

It's a no brainer.



If you want the performance option, then do that.



It is possible that running rich or lean prematurely destroyed the cat. Might need further diagnosis.

Hmm so you think simply measuring the cat temp will do it? I have an IR thermometer...


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[Stomachbuzz]

Originally Posted by vladniko86

Hmm so you think simply measuring the cat temp will do it? I have an IR thermometer...

Yes, this is one of the most direct ways to measure cat performance

[korhun]

Phew.. Thank god the thread is not about what I've understood from the title..

[NoHaveMSG]

Originally Posted by vladniko86

Hmm so you think simply measuring the cat temp will do it? I have an IR thermometer...


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Pre-cat and post-cat measurement. But without a baseline on what a normal cat is, it isn't going to tell you much except what yours is currently reading.

[vladniko86]

So I went around the block and got the car to operating temps.


https://share.icloud.com/photos/09Yy...NUq0t-11kA5x9Q


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