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Old 04-25-2014, 07:44 AM   #1
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Possible solution for CEL when using headers on 2000+, an O2 spacer with a mini-cat..

My son is having a 420 on his 99 Miata - Catalytic Converter not operating at efficiency (paraphrasing...) Apparently this is common on 99-2000 Miatas. it has a new cat but this code is still popping from time to time.

While researching on the Miata forum some folks have had success with an O2 spacer, that has a mini CAT in it.

O2 Simulator Mini Cat Cel Fix best oxygen sensor simulator made.

I thought it was just going to be another spacer (and this vendor sells the spacers too) but it has a little honeycomb of catalytic converter material in there.

I know some boxster folks get a CEL when putting in performance headers because they lose the first set of cats, and the performance headers with the sport cats are super $$$, so I thought I would pass that along.

I may buy this for my son's Miata but first I am going to make sure that the other causes are eliminated (exhaust leaks and so forth), but I just wanted to pass it along.

Has anyone ever seen or used anything like this before? Is the regular spacer usually good enough?

Thanks

Steve
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Old 04-25-2014, 08:22 AM   #2
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My '06 cayman S has headers with hi flow cats and I get cat efficiency codes with them. I've tried both the regular spacer and the mini-cat spacer and neither of them worked in my case. It may be a different story in the earlier cars. My '98 spec boxster has the secondary O2's hanging in the breeze and does not set any codes.
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Old 04-26-2014, 06:26 PM   #3
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steve, unless where your son lives does obd2 emissions checking he could just install a bung plug and zip tie the o2 sensor out od the way to keep the cel from tripping. there are quite a few forum topics on this in various Miata forums forum.miata.net is one which I visit regularly and has a huge amount of information.
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Old 04-27-2014, 01:49 PM   #4
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We are in FL where apparently you can run straight pipes on a rusted out death trap and nobody seems to care We might try the $15 spacer first; I just have to get under the car and see whether we need the straight one or the right angled one.

We have vehicles from the same family; I have a 2007 FJ as my DD and also two old tacomas; one I bought new in 96 which they will have to pry from my cold dead fingers and a 99 for my other son. I tried really hard to like the MR2 Spyder (since I do love Toyotas) but the love just wasn't there...
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Old 02-12-2017, 12:42 PM   #5
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Reviving this old thread

Has anyone here seen any long-term success with keeping the CEL light off in their de-catted 986 by using one of these mini-cats?
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Old 02-12-2017, 03:30 PM   #6
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Since posting this thread I haven't heard of anyone successfully using them... Fabspeed sells some that may be better than the ones I posted, and they can also provide a tune that may resolve it.

I decided just to.keep the stock manifolds.
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Old 02-12-2017, 05:03 PM   #7
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EU 986 cars only have 2 catalytic converters. The headers are straight. They don't have a SAI. One idea might be to flash the ECU with a EU/ROW file. But that won't work with no cats. The ECU gets lambda signals from before and after the cats. So 2 cats and 4 lambdas.

Maybe someone can reprogram the ECU so it does work without cats. But you'll need at least 2 lambdas to run the engine management correctly. And the adaption has to be done to each engine / ECU software version specific.

Optional it might be possible to manipulate 2 of 4 lambda inputs. Lambdas seam not to be can bus controlled, which makes it simpler.

Regards, Markus
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Last edited by Smallblock454; 02-12-2017 at 05:13 PM.
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Old 02-13-2017, 02:24 AM   #8
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Quote:
Originally Posted by Smallblock454 View Post
EU 986 cars only have 2 catalytic converters. The headers are straight. They don't have a SAI. One idea might be to flash the ECU with a EU/ROW file. But that won't work with no cats. The ECU gets lambda signals from before and after the cats. So 2 cats and 4 lambdas.

Maybe someone can reprogram the ECU so it does work without cats. But you'll need at least 2 lambdas to run the engine management correctly. And the adaption has to be done to each engine / ECU software version specific.

Optional it might be possible to manipulate 2 of 4 lambda inputs. Lambdas seam not to be can bus controlled, which makes it simpler.

Regards, Markus
My UK car has had a single pair of 100 cell cats. I've tried the lambda spacers and they don't work long-term. I'm told you can get the secondary lambdas mapped out.
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Old 02-13-2017, 06:17 AM   #9
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You can do a lot of things if you have PST II with dev mode. But as said, it depends on ECU hard- and software version.

On the other hand you can do reengineering things electronically / mechanically. But it takes a lot more time.

Never understood why this funny lambda spacer should work on a 986. Just another not very versatile solution. Maybe it's a good idea to learn what different kinds of lambdas are used in the automotive industry which kind your 986. That might be a good starting point for further decisions.

Sorry, just my 2 cents… as always

Regards, Markus
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