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Fuel tuning: MAF Scaling vs injector pulswidth map

Practical Reflash Tuning

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Hi, I'd just like to clarify something that's been bothering me a little bit.

The BMW ecu's I'm currently looking at tuning (MS41.1, MS42, MS43 and MS45.1) dont have a lambda target map, instead the fuel maps are defined with rpm and load and have an injector pulsewidth lookup. In the Practical Reflash Tuning courses, I haven't heard any mention of tuning the fuel map themselves, just the MAF scaling to get the desired air fuel ratio. If I've understood correctly, its because the lambda target (and in the case of these ecu's, the fuel maps) are perfectly tuned from the factory, and so it's better to adjust our position in those maps rather than the value of those maps. Is this correct?

Guyllaume, I share your pain. I am sorry to say I do not quiet understand you question but I lived through the lambda vs fuel map as my first true, tuning project. I have an MS41 in my e36 328iS with an M50 manifold swap. Initial runs showed high end WOT lambda values of .7. This is insanely rich. I started with MAF Scaling from cruise RPM through STFT errors. Then the mentioned WOT run from above was tuned by MAF Scaling. I tried changing the Pulse Width at those high end areas but the tune would not respond, leading me to believe the MAF Scaling was still off. Using the correction factor from Andre, the MAF Scaling was dialed in and I could now tune the injectors for a lambda of .9 as I desired. I had to go back and forth about 14 times to dial in the tune and I am very happy the results although lacking some closure. I wish I knew how to set the AFR to a static value for MAF Scaling however, as this is what Andre shows and it also makes the error that much more clear. We don't have this option it seems but I was still able to achieve my goal. I used the Innovate Motorsports LM-2 for logging lambda and Alientech's ECM Titanium for ROM modifications and Kess V2 for reading and writing. I hope this helps.

Old thread, but worth mentioning:

MS41's main fuel map is meant to be stoich, and STFTs will aggressively attempt to correct this map to stoich when in closed loop.

From there, it uses two Open Loop enrichment tables:

Open Loop Detection table tells it at what TPS% & RPM to switch to Open loop

Open Loop Enrichment table tells it what % Fuel to add vs RPM.

In the WOT region, It adds anywhere from 8-20% fuel depending on RPM. If you are somehow getting 30%, something is clearly wrong.

For a while, I had disabled the WOT Enrichment and using just the default fuel table, but it was a pain to run it this way and eventually just decided to set the enrichment to whatever it wanted, and it's been more or less painless.

Doing all of this is relatively easy with Romraider for file editing, Romraider Logger (which can either read an LM-2 via USB, or feed the 0-5V into the post-cat O2 sensor input if you don't require it for emissions), MegalogviewerHD for reviewing logs, MS41Quickflash for read/write.

The "OpenMS41" Wiki has tons of stuff on how to connect with this ECU for flashing or datalogging.

I would absolutely not change the MAF sensor scaling unless you have changed the MAF in some way (Resistor, aftermarket MAF)

Once you start messing with the MAF scalar, you are impacting the load value in ~30 other tables.

I think generally the adjustment of the MAF scalar is for a situation where a fuel map is not available, and I have never heard of someone doing it on MS41.

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