No Primary Cat? No Tune? Runs Lean?

[chibich]

Originally Posted by Rekrul

I guess, the ultimate question is how well does the M3's ECU accommodate to the lack of the cat? I mean it seems that we all agree that it will run richer, I just wonder if it is running just a tad bit richer... or if it is going to lead to problems(fouling, massive carbon deposition, etc).

It's not going to run so rich that it will cause problems. Nothing to the point of significantly decreasing the life of the plugs or causing any other problems. Good way to get rid of any extra carbon build up is a good "italian tune up", aka get on it every once in a while haha.

[Rekrul]

Originally Posted by chibich

It's not going to run so rich that it will cause problems. Nothing to the point of significantly decreasing the life of the plugs or causing any other problems. Good way to get rid of any extra carbon build up is a good "italian tune up", aka get on it every once in a while haha.

LOL... I guess that doesn't sound so bad.

[Rekrul]

Originally Posted by Malekreza11

It actually will run rich, not lean.

Just how rich? I know you have extensive knowledge with regard to these motors What are your thoughts?

[BPMSport]

Originally Posted by Rekrul

Just how rich? I know you have extensive knowledge with regard to these motors What are your thoughts?

Sorry for the slow reply... I'm pressed for time.

The ECU will do it's best to adapt to the targets set in the code. I really wouldn't worry about it - in order to foul the plugs you are going to have to be running MUCH richer than than your car would be, and over a long period of time.

It's not like changing the cats is going to make you go from a 13:1 AFR ratio down to 10:1. It's going to be a minimal change and the ECU in this car is quite sophisticated. What you are smelling at the tailpipe is not necessarially the car running much richer - the change in smell is more attributed to the change in exhaust gases comming out of the rear tail pipe due to the absense of cats.

It will not make optimal power as there are some changes than can be made to fueling, timing, and vanos to get the most power and performance out of the car, but it certainly won't cause any damage whatsoever. The ECU simply will not allow the engine to run out of spec. You'll be in limp mode way before that point.

One very important thing to point out is the masking of the CEL. If the CEL comes on for cat efficiency, down the line you could have many other faults that you wouldn't know about because the light is already on. Keep this in mind, as you want the CEL to alert you when there is an actual problem. I do not like methods like the Akra Delete-R, I would do it right or not do it at all.

Someone in an earlier post spoke about not being sure if the M3 is MAF or MAP based. It is MAP based and based on that sensor reading it calculates airflow in kg/h. The pre cat o2 sensors will try to keep part throttle at lamda (14.7), and the post cat o2 sensors shouldn't have any influence as they are simply checking if the cat is doing its job.

I hope this helps.

[Rekrul]

Originally Posted by Mike Benvo

Sorry for the slow reply... I'm pressed for time.

The ECU will do it's best to adapt to the targets set in the code. I really wouldn't worry about it - in order to foul the plugs you are going to have to be running MUCH richer than than your car would be, and over a long period of time.

It's not like changing the cats is going to make you go from a 13:1 AFR ratio down to 10:1. It's going to be a minimal change and the ECU in this car is quite sophisticated. What you are smelling at the tailpipe is not necessarially the car running much richer - the change in smell is more attributed to the change in exhaust gases comming out of the rear tail pipe due to the absense of cats.

It will not make optimal power as there are some changes than can be made to fueling, timing, and vanos to get the most power and performance out of the car, but it certainly won't cause any damage whatsoever. The ECU simply will not allow the engine to run out of spec. You'll be in limp mode way before that point.

One very important thing to point out is the masking of the CEL. If the CEL comes on for cat efficiency, down the line you could have many other faults that you wouldn't know about because the light is already on. Keep this in mind, as you want the CEL to alert you when there is an actual problem. I do not like methods like the Akra Delete-R, I would do it right or not do it at all.

Someone in an earlier post spoke about not being sure if the M3 is MAF or MAP based. It is MAP based and based on that sensor reading it calculates airflow in kg/h. The pre cat o2 sensors will try to keep part throttle at lamda (14.7), and the post cat o2 sensors shouldn't have any influence as they are simply checking if the cat is doing its job.

I hope this helps.

You're the man! I guess with regard to the delete-r isn't it essentially doing what most tuners do with regard to the cel? I mean if you have any other issues come up that would necessitate the light coming on, the delete R will not interfere with that process. Or am I wrong?

Furthermore if you had to pick between a stock x pipe with just primary cats removed vs a fully catless resonated x pipe (IE dinan, AA). Which would you choose? Cost not being a factor?

[bigjae1976]

Question. If I get a tune for no cats and then re-install the front OEM cats for inspection purposes...will the car run fine? My guess is yes, it will just run a little rich.

Originally Posted by Malekreza11

It actually will run rich, not lean.

I thought when you increase exhaust flow the car runs lean.

[Malek@MRF]

Originally Posted by bigjae1976

Question. If I get a tune for no cats and then re-install the front OEM cats for inspection purposes...will the car run fine? My guess is yes, it will just run a little rich.



I thought when you increase exhaust flow the car runs lean.

The car will compensate for that and add fuel, and every single time, it will add too much fuel, causing the AF mixture to be on the rich side.

[bigjae1976]

Originally Posted by Malekreza11

The car will compensate for that and add fuel, and every single time, it will add too much fuel, causing the AF mixture to be on the rich side.

Makes sense!