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

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.

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.

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... :)

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?

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.

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.

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