NefMoto

So, according to vag-com, croup 3, in idle, there is airflow about 3.7-5 g/s, on very light cruise about 30 g/s.
But, when i am looking in MLHFM (551F rs4 SW), there is minimum value of airflow=124,6 kg/h=34,6 g/s (at 0v on MAF).

Question is: how ME7 know about airflow value, when it below MLHFM minimal limit, for example at idle and very light cruise? Is it calculated with math-model, or how?

good question.. I'd like to know the answer to this as well.

I have the issue where my idle AFR's are ok.. but anything below 22ih Hg of VAC (so just barely touching the throttle) the AFR's fall to 12's or even 11's.  I noticed that the inj. PW never goes below 1.7ms which is probably why. And the min. on time is set to 0.50ms so it's not that parameter.

Where to correct this I have no idea.

Not looked into this fully, but there is an offset on the Bosch sensor which means it can give negative readings.

Rick

Is this a physical offset (negatve voltage value from MAF output) or map for offset? When MAF is replaced (for example S4-RS4), the only MLHFM and KFKHFM (right?) changed and all work good including idle.

map offset, not negative reading.

Not sure if this is relevant, but for bosch files, MLOFS is 200kg/hr but 0 for hitachi files.

200kg/hr is approx 55 g/sec

Yes, last night i am study functionrahmen. Look at the page 262. all about pulsation corrections=1, because SY_turbo=true. Other things is not so difficult at first look: signal voltage from maf go through MLHFM, after that trough  GGABT (what this?), after that from this signal MLOF subtracted, then multiplied with KFKHFM, and roughly maf signal is ready.

After that, i compare MLHFM for 2.7tt hitachi maf and 2.7tt bosch maf. Hitachi start readings from near zero g/s, and MLOF=0. Bosch start from about 36 g/s, and MLOF=200. So, i think answer is= (AIRFLOW at aidle/low loads)=(signal from first few cells of MLHFM)-(MLOF). But i dont lok at the MLHFM for bosch NOT rs4 maf, and MLOF for this maf.

But there some lack of understanding about KFKHFM. I think recently, that this map is related to MAF specs. But in functionsrahmen, i read that this map is engine-related (camshaft, VE, and other specs). Next week, my task will be instalation of RS4 maf on 1.8t engine. So, change MLHFM and MLOF on RS4 specs is simple, but what about KFKHFM?? As i understand, entire map from RS4 will totally not work for 1.8t engine?? 

It's simple... Аrithmetically averaged реr segment HFM value.
I.e sum of scans (usually 1 scan per ms) divided by the number of scans of the last segment.

Gremlin thank you again!) Maybe you can tell something about KFKHFM?

It's hard to recalibrate KFKHFM ideally using road run or dyno run tests.
Until you put standalohe engine on specially motor-tester equipment it can take a long time.
But you can do some experimental aproximation enough for real life.
Start with KFKHFM=1.0 and try correct it corresponding fuel/ignition results of engine operation. 

I did the same think as i was trying to make the engine to burn leaner. I simply lowered the values in KFMHFM in the areas i wanted to lower the injection period. Also if you want to go leaner you can adjust the injection times using FKKVS. The minimun injection time won't make the trick.
Sorry about my english. ;)

Well I tried this today.. I lowered the first column (9.7 I think) in KFMHFM from 1.0 to 0.90 and it didn't do anything...

My problem is maybe slightly different and I'm gussing FAR out of the range of the MAF correction table at that point.

To give you an idea.  It runs mid to low 11 AFR when I barely give it enough throttle to get out of overrun, and slowly goes up to 1.0 lambda as I give it more throttle.

I really don't know where else I should look, I'm guessing fuel system correction table?  I'd have to check but I'm guessing the inj. pulse width is still not going lower then 1.7ms (which is obviously too high.  Why this is I have no idea.

What is your TEMIN?

ETA Oh lol nvm i saw you lowered it. Odd.

i had the same problem. As soon as i was touching the accelaration pedal it was goind too rich. At higher pedal values it was ok. I was using stock injectors at the time and i didn't think right to mess with injection latences at the time, but it prouved that i had to lower them a bit and to adjust FKKVS and KFMHFM as well. Then everything was ok. Good luck.

Thank you guys! I will try to play with KFKHFM and FKKVS

Ok question...

does anyone know how the base 1.70ms inj time is calculated?  It clearly seems that it never goes lower then that on my car...  There must be some reason the ECU thinks it needs to keep it at least that high.

Does anyone else know what their min inj time is?

I would guess it is latency + requested on time

(http://www.mre-books.com/sa135/images/sa135_55.gif)

I'm starting to wonder now if my TVUB is just simply too high (even though AFR's are good @ idle and cruise).

Simply because the following:

Warm/Hot start is out of whack (maybe cold start is too rich as well, but the car starts fine when stone cold), I have the issue with light cruise (21+ in. Hg) being too rich, etc.

I got to thinking yesterday that possibly my TVUB values are just too high.  Although I would hope that Bosch was smart enough and make other adjustments so that you could make the TVUB's as close to what the inj specs are.  It's clear we either haven't found them or know how/what exactly is in calculating the base injection time.

There is the added complication of the intake manifold model. This is mentioned in Greg Banish's book and I have seen it referred to in the funktionsrahmen. The ECU compares actual readings of airflow with those returned by the MAF sensor and will makes corrections as it deems necessary. I don't know how it works in any detail or which map(s), characteristic(s) and constant(s) define it. Banish does discuss the general difficulties in controlling fuelling at idle for any engine system (e.g. Large percentage error in injector pulse) so it's clearly not a trivial exercise to tune idle parameters.

Doug

Generally in KFKHFM if you raise the values does that increase fueling (richer), and the opposite if lowering values (leaner)?

I'm just finishing up translating the GGHFM 57.60 module and it states the following:

Application of the MAF Correction Map KFKHFM:

In regions of no pulsation, the air mass comparison is carried out via the map KFKHFM. In this way, MAF-sensor errors caused, for example, by a problematic installation position can be corrected. For either, the balancing should maintain lambda of approximately 1.0, so the error in calculating the air mass in the exhaust gas is low. The residual errors (lambda deviation around 1.0) are interpreted as a mixture error and are compensated for by the characteristic curve FKKVS in the RKTI 11.40 module.

The values in KFKHM in one of my files cluster around 1.000 and the GGHFM overview flow diagram shows that the output from KFKHM is the multiplication factor fkhfm which then feeds through as a multiplication factor into an air flow reading in kg/hr.

Therefore increasing the values in KFKHM will correct the metered air flow up which should result in an enrichment correction in FKKVS.

Doug

I thought they were air mass corrections, not lambda corrections, so it would be the opposite ... higher means adjust MAF reading up (adding fuel to a too lean area) and lower means adjust MAF reading down (remove fuel from a too rich area).

Do I have it backwards??

No, you're right nyet. I must have got confused by the discussion of lambda at the end. The overview flow diagram, clearly shows that the output from KFKHM is the multiplication factor fkhfm which then feeds through as a multiplication factor into an air flow reading in kg/hr.

I shouldn't have been looking at this forum late at night after a busy shift.  :(

I'll edit my original post to reflect that.

Doug

Also keep in mind that by adjusting KFKHM you are adjusting the load that ECU can read. For example in my car i was getting some severe ignition retard (cf) although i have lowered my basic ignition maps enough. When i adjusted the KFKHM i managed to scale up the load that ecu reads and so my ignition and fueling also restored. This map is related to hardware moddifications that can increase airflow to the engine such as front mound intercooler with custom metal pipes bigger or modyfied airbox bigger valves etc. It is a very smart map and you must play with it in order to fine tune your ecu. Sorry for my english i wish you got the point.

Thanks guys for the good info!

MLHFM - converts the MAF voltage to air mass.
KFKHFM - corrects the air mass based engine speed and load.
KFMLDMN - is the minimum air mass based on engine speed and throttle angle.

There is also a global minimum for air mass, and an offset for the air mass after it has been converted from voltage using MLHFM.

For injection time there is a constant that determines the minimum injection time. Even if you want to inject less than this the ECU never will. This minimum injection time is applied after the calculations for injector scale and injector latency offset.