stock tune, aftermarket intake, O2 sensors and the track

[sabbanick]

So I spent the weekend down at Summit Point for hyperfest and the HPDE. Temps were humid in the mid 80's with scattered light rain on sunday. My car has the following modifications .. Gruppe M intake, supersprint X pipe and sport cans. This was my fifth event of the season with this setup and my first SES light.

I threw a SES light after my third session on the first day, scanned the car and it came back with multiple codes for both O2 sensors and their heater cores...no loss of performance noted and I could not clear the codes.

Long story short, I dropped the car off to my local BMW service center and it turns out I cooked my 02 sensors and tripped both fuses for the heater cores. The shop is cool with my mods and said they will honor the 02 sensors but that I should consider getting a tune or running spacers ( hell no ) as im leaning the car out at WOT running stock software and this will only happen again.

The way they explained it makes sense ... the car runs on a closed loop at WOT conditions..meaning there is no variability of the ECU to control fueling (sorry I'm simple minded in my explanations). The problem arises running an aftermarket intake because of the increased air flow leaning exhaust gases under WOT conditions. The increased exhaust temps associated with lean conditions cooked my O2 sensors.

Summit point if your not familiar with track is a small track(10 turns)with a pretty decent straight. The straight for me was a straight rip to the top of 4th gear with a hard braking zone. So the conditions fit to what the dealer is telling me.

Just wanted to put this out there to possibly add another slice of info or point to consider for those considering a aftermarket intake as well a way to get some feedback from members "more in the know" then myself.

Makes sense to me but what do you guys think of the dealers reasoning and there advise?

Currently i am considering getting either evolve's tune or the bimmerworld/epic tune if either will support our cars.

-N

[mfanatic325]

Hmmmm although their explanation seems to make sense on the surface...the more I think about it, the more I want to argue the fact about the aftermarket intake part; where they claim that with the increased intake flow, you're ultimately passing hotter gases ( sorry, that sounded funny to me when I typed it out...).
Unless an aftermarket intake TRULY flows better than say, a drop-in filter--which I highly doubt--then it might be credible.
Because I run a drop-in filter and have never had SES/code issues.

And it's also surprising that the OEM ECU (which should be PLENTY well-ironed out) can't compensate for the difference of intakes...

But then again I do have a tune (along with a bunch of other stuff lol), so perhaps all that covers for it?

[sabbanick]

If the car goes into a closed loop circuit at WOT then this makes sense as the ECU can't adjust amount of fuel it adds into the system (under all other conditions it has the ability to). That is, as you state, IF the Gruppe M flows more then a drop in filter . All i know is I blew both my O2 sensors ...

The good news is that the car is back in action and the service was under warrenty. I am waiting on bimmerworld to get back to me. They say they can do the flash but that it will take a little longer than it would for the E46. Im still trying to confirm if the have flashed our ECU and if the files are any different then the E46 one.

If bimmerworld falls through ill most like go with the AA tune.

Next track day is last weekend in July back at Summit Pt. so I will make a decision sooner then later with who I go with.

[Shipkiller]

They don't know what happened.

The car will always be in 'closed loop mode' after the O2 sensors heat up (approx. 90-120 seconds). Until the O2 sensors are in their operating temp range which I think is 600', the ECU is in OPEN loop mode and NOT dynamically modifying the mapping..

The reason the SAP (secondary air pump) in installed, is to inject O2 (air) into the exhaust manifold during the first 90 seconds after the engine starts to help burn off unburnt hydrocarbons and heat up the O2 senors so the car gets into 'close loop' mode faster and not relying on a pre-programmed map.

Also, the EGT (exhaust gas temp sensor) is there to help keep everything balanced. Bad description....

I have over twenty track days on my stock MC and I have never had a issue, even when then ambient temps at VIR were 95'..

[sabbanick]

interesting. Thanks for the response shipkiller.

Is your intake completely stock?

Based on your response is it possible i am mistaking the closed loop mode for an open loop mode? I have been know to mix up my left's from my right's before

open loop mode - ECU predetermined engine settings, no adaptability in its control
closed loop mode - ECU controls settings based on EGT, O2 sensors, ....


I can't wait to make it to VIR, there is a chance I may go this November with the Audi club. Its a far drive from NY.

[pokeybritches]

I was writing a response during lunch but ran out of time. Yes, you're confusing open and closed loop systems. Closed loop systems have feedback control, which is typically more optimized as far as efficiency and performance are concerned. Open loop systems are generally less adaptable and capable. Most older cars ran in open loop mode at WOT, causing a very rich fuel/air mixture. The car would ignore most sensors and just send a sh!tload of fuel into the engine, erring on the side of a rich mixture to avoid a lean condition. Marketers of "chips" for these cars tried to sell their products by claiming that their chips caused the ECU remain in closed loop mode at WOT (vs the stock open loop mode), which is why they felt they could scientifically justify increasing both economy and efficiency. I've read that new BMW's utilize closed loop control all the time, even at WOT. Here's a picture to help (I claim no rights to it):



The closed loop system has feedback control. Now, I have a few questions.

1. How does the dealer know the car was in a lean condition at high RPM?

2. Would a lean condition fry an O2 sensor?

OT: I do believe an aftermarket intake allows the engine to breathe more easily. I'm going off of the fact that I've taken apart the stock intake and looked at it like a rational human being. There is no way the stock intake flows as well. There is a chance it could pull in cooler air, but even then I'm not so sure it makes any difference. Can the car utilize that extra airflow? I don't know. I don't want to get into this debate (again).

[sabbanick]

Ok cool, thanks for straightening that out and sorry for any confusion it may have caused to anyone else.

As for your guestions i will try to tackle them all at once. The dealer knew I was at the track when the SES appeared and upon their inspection both fuses to O2 heater cores were tripped.

AS far as I see it, the dealers diagnosis of why this happened is based on a few things...their knowledge of S54 engine management systems and how my aftermarket intake influenced it especially in an on track environment where repeated, sustained periods of WOT occur unlike typical street conditions.

Generally speaking ...Think it is safe to say that if you are flowing more air into the system and the system being in a open loop can't counteract by adding more fuel then things are going to shift toward the side of a lean mixture.

Leaning out the fuel mixture will raise temp of exhaust gases, in my case it seems the temp in the headers got hot enough to trip both fuses to the o2 heater cores causing the SES light I could not clear. I did not overheat my car nor were my oil temps raising to a concerning level at any point during the track sessions.

Following the dealers logic, an aftermarket tune will change the mapping under WOT conditions (open loop) at take into consideration the increased amount of air my car adds to the system over stock setup. IF this is the case then my next issue is finding the right tune...


I posted this thread mainly because there are a lot of holes in my knowledge base and its always nice to get some non-biased feedback for others. At this point I am still taking a lot of this at face value and Its obvious that I am leaning towards the advise of my dealer...

It difficult to elaborate on things your still trying to get a grasp on...hope I am making sense and am somewhat clear in my explanation.

[pokeybritches]

I would search more into whether or not the newer BMW's, specifically those with the S54, are in closed or open loop mode at WOT. I thought they were more advanced and stayed in closed loop mode, but your dealer is saying otherwise.

Another possibility is that the intake causes certain readings to be out of parameters; the engine is metering the maximum fuel the ECU is programmed to allow it to meter, but it's not keeping up with demand. I'd hope it would throw fault codes if that was the case. I don't think this is likely.

The ECU could possibly record max EGT, duration over x degrees, and the odometer when temps were up. If that's the case, pull it off the ECU.

Aren't there products that allow you to read the A/F ratio in real time?

[sabbanick]

Originally Posted by pokeybritches

I would search more into whether or not the newer BMW's, specifically those with the S54, are in closed or open loop mode at WOT. I thought they were more advanced and stayed in closed loop mode, but your dealer is saying otherwise.

Another possibility is that the intake causes certain readings to be out of parameters; the engine is metering the maximum fuel the ECU is programmed to allow it to meter, but it's not keeping up with demand. I'd hope it would throw fault codes if that was the case. I don't think this is likely.

The ECU could possibly record max EGT, duration over x degrees, and the odometer when temps were up. If that's the case, pull it off the ECU.

Aren't there products that allow you to read the A/F ratio in real time?

I like that your making me think outside "the box" the dealer has put me in.

The only codes I threw where related specifically to the O2 sensors and their heater cores (P0031, P0037, P0051, P0057). Other then the SES the car performed flawlessly on the track the only thing holding 'er back was the nut behind the wheel.

Is there an OBD tool that lets you pull info from the ECU and interact with it like there is for audi/VW's (Ross tech's VAGCOM)? I was borrowing a universal reader/scanner from a buddy to read the codes at the track.

The only way to get live AFR's would be via a wideband, something I am not considering doing.

[pokeybritches]

Would this not work? http://www.autoenginuity.com/index.html There's software on the Classifieds section.

My dad just fried an engine because the fuel pump wasn't keeping up with demand. The car didn't throw any codes. I've been considering getting a AFR or fuel press gauge to go in the third slot of an ashtray gauge kit (water and oil press being the others).

[Shipkiller]

I would find it VERY, VERY unlikely that BMW would put the S54 into open-loop mode at WOT.

Also, would not the EGT start to intervene if the exhaust gases got too hot and started to destroy the O2 sensors?

Having been on various BMW boards for years and have seen the posts that indicate that the S54's O2 sensors fail on a higher than average rate than other cars. Also I have seen reports on this board and other boards that a dealer that really knows the S54 are few and far between. There are others who track their cars that have aftermarket intake systems and have no issues.

Is it possible that you just 'rolled craps' and had both sensors go at the same time? This is possibility.

I really have a hard time believing that your intake overpowered the ECU as it were. The MSS70 ECU that the Z4M uses is a newer, faster, better ECU than the MSS45 that is use on the E46M3.

The only person on this forum that I know who would have a definitive answer to the WOT question would be Ocha, unless someone from ESS or one of the other tuners would provide the answer.

[sabbanick]

Originally Posted by Shipkiller

I would find it VERY, VERY unlikely that BMW would put the S54 into open-loop mode at WOT.

Also, would not the EGT start to intervene if the exhaust gases got too hot and started to destroy the O2 sensors?

If the car is under open loop mode at WOT then no the EGT sensor would not intervene.

well i just sent my ECU out to get bimmerworld/tune

wish I had catless headers to really get some gains from the tune.

[Shipkiller]

Originally Posted by sabbanick

If the car is under open loop mode at WOT then no the EGT sensor would not intervene.

Yea, I assume that also. It would not make sense for BMW to disable the engine safety protocols under WOT...

[sabbanick]

Originally Posted by Shipkiller

Yea, I assume that also. It would not make sense for BMW to disable the engine safety protocols under WOT...

Here lies all the speculation. Wish we knew the hard facts!