ECU maps & AFM voltage and MAF conversions (long)

[Jeff N.]

OK - here's a summary of some stuff that I've been trying to muse through as I ponder the effect of the MAF conversion on my setup. I think these are trueisms....challenge as you wish. Posted for interest and to stimulate thought.

All related to the M30 setup.

1 - the AFM has a voltage range of basically 0 to 5 volts. The output voltage is based on the angle of the flapper door.

2 - the AFM flapper door goes to a maximum angle before before the engine reaches maximum RPM. Exact point is not 100% clear - I've heard suggestions that this occurs at about 3000 to 3500 RPM at WOT. Never tested it though. I have no clue at what point, if ever, the AFM reaches max flapper angle at anything less than WOT.

3 - The ECU selects the correct fuel map (mid map vs WOT map) based on the TPS. If the TPS stays WOT, then the ECU ignores the AFM flapper and bases fuel and advance on the engine RPM only.

4 - If the TPS has not signaled WOT, then the mid map is used and the fuel and advance settings are a function of the engine RPM and the flapper door angle. The flapper door angle is basically synonomous with the "load" on engine. This is sent to the ECU as voltage between 0 and 5 volts.

5 - A MAF sensor replacing the AFM has the ability to "process" more air flow than the AFM. This means that a MAF can measure more air passing thru the unit before it is maxed out.

6 - When either a MAF or AFM is maxed out, it will send 5 volts to the ECU.

7 - For a MAF kit to correctly "work" in the 535 the following must be true. For a given amount of airflow, the output voltage of the MAF must be the same as the output voltage of the AFM. If the MAF sends less voltage for a given amount of air, the ECU assumes less load and the mixture will tend to be lean. If the MAF sends more voltage, the ECU assumes more load and the mixture will tend to be rich. Timing will also be effected.

8 - The MAFs ability to spoof the ECU via changing the "load" (voltage) gives you a basic ability to "tune" your mixture. However, this "tune" only changes the relative lookup in the WOT and Mid throttle maps. The map profile contained in the chip is not modified or effected.


Sooo...there seem to be a couple of interesting thoughts or questions - assuming this is more or less true.

a - tuning your mixture by modifying the voltage output of the MAF relative to airflow can have unintended consequences on the timing. The more you spoof the ECU on the airflow, the more likely you are to have an unintended timing change.

b - it's likely better to modify the fuel and ignition maps to be correct for your (modified) engine and do only very nominal fine tuning via the MAF.

c - The best MAF setting is as close to a 1 to 1 relationship as you can get with the AFM. The only way to calibrate your MAF voltage to the AFM voltage is to compare the two on a flowbench. (BTW, this is done for you with a base 535 voltage curve with the Racing King MAF).

d - I think - At less than WOT on the TPS, the AFM flapper must not ever reach max angle. At not WOT on the TPS, you are running the mid range map and you need two inputs to locate the correct fuel and timing value - load and RPM. If the flapper reaches max angle while the engine conditions are still changing, there is no way for the ECU to measure and adjust mixture and timing. The purpose of the WOT map, which determines values ONLY based on RPM, is to account for the flapper door going to max angle.

BTW - I really like the MAF kit on my car. There's no question the car runs better. I'm just trying to get my arms around what tinkering with the voltage table in the control box really does.

Hmmm...ok. That's enough for now. Thoughts?

Jeff

[Robin-535im]

Great thoughts Jeff. Been thinkin' some myself...
1 and 2 sound like I expected.


3 - The ECU selects the correct fuel map (mid map vs WOT map) based on the TPS. If the TPS stays WOT, then the ECU ignores the AFM flapper and bases fuel and advance on the engine RPM only.
So then WOT map should be more customized to your particular setup than mid-map because there's only one free variable, RPM. Mid map can be more generic and tweaked by MAF settings.


4 - If the TPS has not signaled WOT, then the mid map is used and the fuel and advance settings are a function of the engine RPM and the flapper door angle. The flapper door angle is basically synonomous with the "load" on engine. This is sent to the ECU as voltage between 0 and 5 volts.
So - you want to tune the mid map to match fuel and timing assuming correct MAF readings, then tweak MAF at the dyno to optimize...

5 - A MAF sensor replacing the AFM has the ability to "process" more air flow than the AFM. This means that a MAF can measure more air passing thru the unit before it is maxed out.
So you get a finer, more accurate measurement of the air flow, meaning that your fuel/timing maps can have more detail to them... i.e., be tuned more tightly to your car's dynamics...

7 - For a MAF kit to correctly "work" in the 535 the following must be true. For a given amount of airflow, the output voltage of the MAF must be the same as the output voltage of the AFM. If the MAF sends less voltage for a given amount of air, the ECU assumes less load and the mixture will tend to be lean. If the MAF sends more voltage, the ECU assumes more load and the mixture will tend to be rich. Timing will also be effected.
Conversely, you can tweak sub-optimal settings in the mid map by spoofing the ECU - if the map is too lean at a certain flow, you can tweak the MAF reading the give you a better mixture. - wait, that's what you say in 8:

8 - The MAFs ability to spoof the ECU via changing the "load" (voltage) gives you a basic ability to "tune" your mixture. However, this "tune" only changes the relative lookup in the WOT and Mid throttle maps. The map profile contained in the chip is not modified or effected.

Sooo...there seem to be a couple of interesting thoughts or questions - assuming this is more or less true.

a - tuning your mixture by modifying the voltage output of the MAF relative to airflow can have unintended consequences on the timing. The more you spoof the ECU on the airflow, the more likely you are to have an intended timing change.

b - it's likely better to modify the fuel and ignition maps to be correct for your (modified) engine and do only very nominal fine tuning via the MAF.

c - The best MAF setting is as close to a 1 to 1 relationship as you can get with the AFM. The only way to calibrate your MAF voltage to the AFM voltage is to compare the two on a flowbench. (BTW, this is done for you with a base 535 voltage curve with the Racing King MAF).

d - I think - At less than WOT on the TPS, the AFM flapper must not ever reach max angle. At not WOT on the TPS, you are running the mid range map and you need two inputs to locate the correct fuel and timing value - load and RPM. If the flapper reaches max angle while the engine conditions are still changing, there is no way for the ECU to measure and adjust mixture and timing. The purpose of the WOT map, which determines values ONLY based on RPM, is to account for the flapper door going to max angle.

I'm with you, except for c should be "best starting setting" so you can tune it later. The biggest question I still have is how does the O2 sensor change it? I believe the O2 sensor operates closed loop, controlling the exhaust gas to the stoiciometric balance best for emissions by tweaking either the timing or fuel or both. This tells me you'll negate the changes your chip made if the chip was trying to put you at a mixture tuned for power, not emissions.

Then again, the O2 circuit runs a 1Hz (one update per second) right? Maybe the ECU works faster, hence the O2 circuit can't catch up to it when the mixture is changing, i.e., when you're climbing through the RPMs. Once you stabilize, the O2 system tunes your engine back to better emissions.

What if the O2 sensor was disabled or spoofed too? Well, then you could tune the engine more, but probably dump too much fuel into the cat and burn it up. Maybe it's okay for WOT range, but you wouldn't want to run it off stoic all the time...

BTW - I really like the MAF kit on my car. There's no question the car runs better. I'm just trying to get my arms around what tinkering with the voltage table in the control box really does.


Hate to hear you say that, now I want one too... :)

[Robin-535im]

Then again, the O2 circuit runs a 1Hz (one update per second) right? Maybe the ECU works faster, hence the O2 circuit can't catch up to it when the mixture is changing, i.e., when you're climbing through the RPMs. Once you stabilize, the O2 system tunes your engine back to better emissions.


In fact, that might explain the pulsing I get when climing a gradual hill. 2nd gear, slowly accelerating up a hill, my car pulses, as if the mixture is being tweaked once a second... Maybe this is the lambda circuit fighting the EAT chip? Every one second, the mixture is tweaked back to the "better emissions" setting but the O2 system, but in between the chip dumps in a little more power.

[Martin in Bellevue]

I've been playing with the minute changes available with the maf software lately. The sharply rising curve from origin is intended to mimic the stock air box flapper resistance. It does seem to smooth things out in the mornings. I guess the whole curve sits a bit left of things due to the 21 pound injectors? The existing curve was taken primarily from the settings retained from the dyno session tune. We'll see how far things have deviated with another dyno session in a few weeks.

http://www.bimmer.info/bmw/Martin5er/21lbMAFJuly1904.jpg

I'm not too interested in engaging in the motronic discussion as I seem to understand conflicting theories of its operation. I'd hope the O2 sensor controls things quicker than once per second? I'd also like to know the finite range of the stock air meter, as 5v may be off, I dunno.The stock air meter doesn't work off 12v as expected, but the 4.something, if memory serves. I suspect our MAF settings may be peaking higher than needed.

[Jeff N.]

I wouldn't be surprised that it's the lamda circuit trying to make adjustments. Without a good mixture meature, hard to know if the lamba circuit is trying to lean or richen the mixture.

Try it open loop and see what happens. Just unscrew the O2 plug underneath the starter.

Jeff

[Jeff N.]

I think that bundle curve is from when Derek sent in that AFM a while ago - before the next gen setup. Is that the curve from the dyno session?

I'm beginning to think 8 degrees is a bit too much advance on the cam. Top end is suffering a bit. Thinking we try either the 5 or the 7 setting on the Korman gear.

Set a schedule for your cam yet?

Jeff

[Jeff N.]

So then WOT map should be more customized to your particular setup than mid-map because there's only one free variable, RPM. Mid map can be more generic and tweaked by MAF settings.

Hadn't considered that. Interesting thought.


So - you want to tune the mid map to match fuel and timing assuming correct MAF readings, then tweak MAF at the dyno to optimize...

Yup. That's what I'm thinking. Only tweek via the MAF.


So you get a finer, more accurate measurement of the air flow, meaning that your fuel/timing maps can have more detail to them... i.e., be tuned more tightly to your car's dynamics...

I'm not sure the measurement is better. The map detail is fixed - there are a set number of data points in the map. I think the trick is to have the correct map values for a given lookup point.


I'm with you, except for c should be "best starting setting" so you can tune it later. The biggest question I still have is how does the O2 sensor change it? I believe the O2 sensor operates closed loop, controlling the exhaust gas to the stoiciometric balance best for emissions by tweaking either the timing or fuel or both. This tells me you'll negate the changes your chip made if the chip was trying to put you at a mixture tuned for power, not emissions.

Yes...best starting point is better phrasing. I think Martin's MAF curve looks pretty good.

I think the Lamda circuit tries to "control" the mixture by sniffing the exhaust output then skewing the injector pulse such that a particular stoic setting is reached. I believe the target for the lamda is based on what's best for the cat, not what's best for HP


Then again, the O2 circuit runs a 1Hz (one update per second) right? Maybe the ECU works faster, hence the O2 circuit can't catch up to it when the mixture is changing, i.e., when you're climbing through the RPMs. Once you stabilize, the O2 system tunes your engine back to better emissions.

Yeah...I wonder too. Never quite understood the learning aspects of the lambda system. Mark's explained it once or twice if I recall but I still haven't quite grocked it.

Jeff

[Martin in Bellevue]

http://www.bimmer.info/bmw/Martin5er/testMAF.jpg

The dyno curve isn't too linear & the bottom starts off high, as there isn't a way to change the initial measures manually with the pots. The previous posted curve is taken from that dyno session, modifying the initial measures near 0 volts to mimic the stock air meter.

Extended family has put the cam stuff off schedule for a few days.

[George M]

...on balance, I agree with what you wrote Jeff. I worked with Bruno on setting up his MAF and the few kits he sold. Your observation about setting the MAF up to replicate the AFM in terms of telling the DME what voltage pertains to volumetric air flow rate is a good one. The reason is the DME uses the AFM as only a reference point for air-flow into the motor and not a device for adjusting air-flow in accordance with ideal air/fuel mixture. That is the O2 sensor's job...to sniff the exhaust and determine combustion temperature and adjust injector duty cycle in accordance with how much air is being ingested per information provided to the DME from the AFM/MAF. There is one consideration however....and that is...the calibration of the AFM from the factory may not be idealized in terms of how much actual air is being drawn into the engine. For all intents however it is quite close and when Bruno was having the prototype MAF flow tested...the curve was derived based upon the stock AFM and not tweaked or offset accordingly. Fooling the DME with a different Voltage versus Airflow curve pays little dividend. Best to provide accurate air volumetric flowrate information to the DME and if desired to optimize air/fuel, best to do so with an EPROM change adjusting injection firing duration (duty cycle) in accordance amount of air reported by the AFM/MAF. In summary, the AFM/MAF is simply a sensor...best to leave its calibration alone which the DME relies upon to crunch air/fuel per the air fuel map encoded into the EPROM be it performance or stock chip.
George

[Jeff N.]

.

[Martin in Bellevue]

It is a stright curve up to 5v both input & 5v output.

George's insight seem to support the need to dyno tuning for emissions. Maybe we should try a session with my car warmed up & the o2 sensor unplugged? Which way would that swing things, against the previous, saved map?

[George M]

happenstance. n/t

[Martin in Bellevue]

It has the early taper down low, that I've been coming up with.

http://www.bimmer.info/bmw/Martin5er/944maf.jpg

[George M]

that's right Martin...was only circumstance that tossed the 535i curve into the Ford directory...happenstance :-)

As you have often said and in Jeff's search to bring out the potential to all the changes he has made...it is all about dyno tuning, in particular the more changes you make deviating from engine stock configuration, the more tuning is necessary to bring changed components into harmony. The stock chip is biased to meeting emissions of course with some loss to ultimate performance potential...even on a stock motor. You could perform a baseline run Martin without the O2 sensor connected, but not sure how much info you would glean. At the end of the day, it is all about optimizing air/fuel combo and ignition timing advance curve(s) you run mostly based on trial and error on the dyno in accordance with what mechanical changes were made to the motor which will feather the best performance edge. Ideally if you do a lot of engine work and aren't happy with the stock or performance chip, then work with someone like Mark D to develop a custom chip based upon particular engine mods/requirements. Or alternatively, purchase a stand alone engine management that you can fine tune yourself to get the most out of the changes you have made.
George

[George M]

Voltage versus Flowrate curve derived by flow testing at ProM while I was there in creation of Bruno's prototype MAF. Martin, as a suggestion, I would adopt this shape curve for your MAF calibration if you want to replicate the factory calibration for the BMW AFM. Again, an AFM/MAF is simply a sensor, and I am of the school, the sensor calibrations should not be tweaked. If you want performance gain, then change the DME calibration per the EPROM based upon real time data provided by factory calibration of MAF and O2 sensors. Will this manifest much change over what you are running right now Martin?....likely not. Even though the curves are different, the end points are probably close and nth level performance is all about max throttle anyway. A change in MAF calibration would likely affect driveability more than nth degree performance.
George
Factory AFM/MAF curve for M30 derived at ProM:
http://members.roadfly.com/georgemann/MAFCurve.jpg

[Martin in Bellevue]

Factory AFM/MAF curve for M30 derived at ProM:
http://members.roadfly.com/georgemann/MAFCurve.jpg[/QUOTE]

[Jeff N.]

I tend to agree that you want to treat the MAF like a sensor and not mess wid it a bunch after it's set.

I also agree that chip tables are the best location to adjust the engines fuel and timing calibrations.

Too bad we don't have a real time way to tweek those chip maps. Mark D's been most helpful with my questions. The difficult part has been to understand and articulate the "current state" (stock chip, EAT chip, you name it) and then decide WHAT you need to do from there. More fuel here, less there, more advance here, less there, etc.

Jeff

[Martin in Bellevue]

I tend to agree that you want to treat the MAF like a sensor and not mess wid it a bunch after it's set.

I also agree that chip tables are the best location to adjust the engines fuel and timing calibrations.

Too bad we don't have a real time way to tweek those chip maps. Mark D's been most helpful with my questions. The difficult part has been to understand and articulate the "current state" (stock chip, EAT chip, you name it) and then decide WHAT you need to do from there. More fuel here, less there, more advance here, less there, etc.

Jeff

[George M]

believe Mark would tell you first hand...creating the right chip...and again different for your MM head/cammed M-30 than my stock M-30 car is largely based upon offsetting existing air/fuel, ignition timing maps as a start point...on an educated hunch of what emmisions standards are typically biased toward and the rest is trial and error on the dyno...taking into account variability to not make the timing map too aggressive due to variation in fuel types and different engine conditions out there. I will e-mail you that file.
George

[Jeff N.]

need to get that friggin cabin o2 meter hooked up.

[George M]

interesting Jeff...believe that was the curve that Bruno ran with his MAF set up.
George

[George M]

your battery for a period of time after installing the new curve into your MAF controller? Maybe your richness was due to your DME not being reset to default values and adapting to the new curve.
George

[Jeff N.]

I think so. I'd have to run the test again as I was also tinkering with ECU chips at the same time.

[winfred]

one of these?
http://members.cox.net/wdixon27/gauges
it's helped me more then enough to offset it's paltry $65 cost, plus it looks neat with the aluiminum trim rings and the plate i turned to mount it in the ashtray


need to get that friggin cabin o2 meter hooked up.

[Jeff N.]

need to fix dat.

[Paul in NZ]

Extremely interesting tho way over my head!I am interested in the "resetting" of the ECU.When i have had my battery disconnected (two times lately battery was on its way out) my idle has been all over the place....settling down now on day 3.What does the ECU have to relearn and why????.

[winfred]

with a stock motor it should not take that long to readjust, over time wear and tear on the motor and sensors change the injection requierments of the motor and the computer adjusts it's baseline settings, you may have a small problem somewear like a vacuum leak, worn plugs, old fuel filter, slow o2 sensor, dirty contacts in the afm, dirty icv, dirty throttle body or something like that


Extremely interesting tho way over my head!I am interested in the "resetting" of the ECU.When i have had my battery disconnected (two times lately battery was on its way out) my idle has been all over the place....settling down now on day 3.What does the ECU have to relearn and why????.

[Paul in NZ]

it does readjust...just before the battery died it was running really well andthe idle was smooth and steady....