Rich fuel settings, low mileage, EPA, catalytic converter, ECU
 

First off: I searched! I promise, I did, I just couldn't find any discussion about my question. If you know of any, please point me to them. :) That said...


Hi,

I've been browsing the boards for a while. I've read many posts about the 'missing HP', and Mazda richening the fuel mixture to meet EPA standards on the life of the catalytic converter. I don't get it. How can this be? I have seen several catalytic converters fail, and all have been due to rich fuel mixtures. Granted, this is on other cars with piston engines.

Would somebody care to explain how a richer fuel mixture would preserve the catalytic converter and help meet EPA standards?

Thanks!

Yoy need to search harder, this has been talked to death....

From my understanding is that the rotary engines run quite bit hotter than piston engines. So the increase in fuel richness will keep the converters cooler instead of burning out the guts of the cats earlier in its life. Keep in mind that this is true when computers from both engines are tuned SOMEWHAT identically from the factory.

I believe that there are other members more mechanically versed than I am in this area but I will do my best to explain. One of the biggest reasons for Catalytic Converters to fail would be due to heat. In modern and more effecient engines we now run them leaner to get an earlier and hotter detination. If we run too lean we run into all kinds of problems so there is a balance. In my parents older cars the cats were just substandard and didn't usually last more than 50k miles. The problem had more to do with the rich fuel ingniting as exhaust gasses being passed through the cat. This late burn was also too hot and killed the cat. Now with O2 sensors and backfire control via electronics we have less of this problem.

It is these same fuel management systems that allow us to run leaner than ever before with much less risk of pre-detenation and allows us to push our engines and makes them more effecient. If you had ever told my grandfather that I would be able to get 475+ hp out of a 2.0L 4 banger he would have laughed in your face. Just attempting such a feet while he was building cars would have meant sudden death to the pistons but on top of that they were under the impression that richer meant faster.

I also understand that another factor in the old cat death problem was the quality of fuel. It was difficult to judge fuel grade and that meant that you could have a large change in cumbustion zone depending on the fuel quality. This would lead to some fuels burning early or late depending.

The theory is that the exhaust temps will be reduced by 'fatting-out' the fuel mixture. However, as you have implied, by using too rich of a mixture, there is the possibility of eventually clogging the cat. As far as I know, there have been no follow-up EPA data for the "post-richening" Renesis emissions...

Regards, Art

the EPA cat story goes like this- Epa said that the exhaust gases going to the cat were so hot that they would burn out the cat before the 120,000 required life expectancy. this is because rotaries, in general, have hotter exhaust gases than pistons. also the renesis sits really far back so the distance between it and the cat is closer than even previous rotaries. so the extra fuel is dumped into the mix for cooling, because it doesn't all burn and with the new port set-up much more of it gets swept around for another combustion cycle and not dumped thru to the cat than in the previous 13b. i have a theory that this extra fuel sitting in there combined with rotarygods dislike for the firing order on startup is the culprit behind the flooding issue.

Sorry...not MikeC. I deleted the post. How did I get signed in as somebody else?

Thanks all for taking the time to reply. I see, it is an issue of exhaust gas temps eating the cats. I didn't know that rotary engines run significantly hotter than their piston cousins. Now I know! Thanks! :)

So is this the reason why it spits fire with the borla exhaust ? because theres extra unburned fuel that ignites in the exhaust ?

Yes. And that fire spitting will mess up the cat quickly too.