MSS54HP tuning larger injectors

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olsboy
Posts: 2
Joined: Thu Apr 22, 2021 6:21 pm

MSS54HP tuning larger injectors

Post by olsboy »

Hi guys, i am in the process of tuning a supercharged e46 m3, and have fitted it with a set of id1050x injectors.
I have scaled them to injector dynamics dead times for these injectors. What i need help here is getting them to idle at 14.7 afr. I have managed to get them to idle fairly well by reducing global fueling down to 0.20 and also changing injection min opening time to 0.45ms, and also reducing fueling in the alpha-N map. I do not know if this is the correct way of tuning fuel with this ecu because lack of documentation or an fdef for the mss54 to see how the fueling is calculated by this ecu.
Car is idling at 14 afr now, but at low load it's a bit lean and hesitates but then picks up ok. Sudden acceleration the engine hesitates because lack of fuel, so i might need to play around with the acceleration enrichment maps to fix this. Wot fueling is ok although kind of rich but i will try to lean it out with the alpha-N fueling map. Maf sensor has been removed that is why i am tuning with alpha-N only for fuelling. Again i am doing all of this by trail and error to see what works and doesn't. So if anyone has experience with tuning this ecu with bigger injectors and supercharger i would be happy for you to help me. Before anyone asks yes i reduced ign timing at high load and mid just for safety.
Renovelo
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Posts: 180
Joined: Thu Aug 08, 2013 7:02 pm

Re: MSS54HP tuning larger injectors

Post by Renovelo »

We haven't tuned for larger injectors ourselves on MSS54 but we hope to soon on our E46 M3!

Based on our knowledge, most tuners start by scaling the global injector factor (K_TI_GA) appropriately along with the base fuel map (KF_TI_N_RF) until the A/F ratio looks good for steady-state driving (no accel/decel) with part throttle. You may have to "incline" the base fuel map with respect to one of the axes to obtain what you want (i.e. sloped with respect to the engine speed axis). This is a common tuning trick for fuel "offset" tables which are relatively flat in their stock form. Afterwards, tuners modify the full throttle fuel table (KF_TI_N_RF_VL) until the A/F ratio looks good for WOT pulls. After the steady-state fuel tables are tuned well, they then turn their attention to the fuel transient tables to handle accel/decel conditions.

As you mentioned, the minimum injector opening time (K_TI_MIN) and the battery offset curve (KL_TI_UB) need to also be appropriately tuned at the very beginning.

This technique usually works well with popular injector sizes for supercharger kits (i.e. 630cc). You may have to try other techniques/tricks for ID1050X injectors which are significantly larger.
olsboy
Posts: 2
Joined: Thu Apr 22, 2021 6:21 pm

Re: MSS54HP tuning larger injectors

Post by olsboy »

Thank you for your help. I did exactly as you told me and had very good result with tuning fuel. Low load and WOT are tuned pretty good now, just need fine tweaking for WOT fueling. The only thing that has been giving me trouble is when you mash the gas pedal it stutters and then it cleans up. Have to play around with that now to get it sorted. Another question i have is do you need to tune the alpha-n map at all, as i see if i reduce or increase values here it also affects my fueling. Also is it possible to add injector duty cycle to your logger?
Renovelo
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Posts: 180
Joined: Thu Aug 08, 2013 7:02 pm

Re: MSS54HP tuning larger injectors

Post by Renovelo »

That's great to hear! Theoretically, you could probably get away without touching the alpha-N table. If you think about what this table represents in normal operation, it tells the DME how much airflow is occurring in the event of a MAF sensor failure. If you don't change this table to account for more airflow from a supercharger, you can probably make up for it in your fuel tuning. The only thing we're not yet sure about is if the alpha-N table is used for other important calculations (like engine load). Once we convert our shop car to F/I, we'll have a vested interested into digging further into the disassembly to learn. ;)

Since this table represents the airflow into the engine based on engine speed and throttle opening, it's probably wise to tune this table. The problem with doing so is that you need to set this table up at the very beginning based on prior knowledge that you probably don't have. It's almost exactly like tuning for a larger MAF. When tuning for a larger MAF, you set this curve based on a spec sheet from the MAF manufacturer and you only make small tweaks to it afterward. If the MAF was calibrated correctly at the manufacturer and your setup matches the calibration setup exactly, then you probably wouldn't touch the MAF curve ever. You then focus your attention to all of the fuel tuning exactly as described previously. If you jump back and forth between tuning the MAF curve and fueling simultaneously, you'll end up "chasing your tail" as we like to often say.

Unfortunately, you don't have a spec sheet for the supercharger which gives you the alpha-N map (on a S54) as a starting point. This makes it challenging to make it your starting point and you'll find yourself tuning both the air and fuel maps simultaneously. There are some tuning techniques to get around this that we won't get into as it would take too long to describe. Honestly, we always recommend reading the books that Greg Banish has published on tuning. Although not BMW-specific, some of his books talk in detail about MAF-based tuning and they're very applicable to BMWs. He does a good job explaining the difficulty of tuning air and fuel simultaneously, and methods to prevent having to do so. Specifically, he talks about tuning for a larger MAF and not having a spec sheet to use as a starting point.

To answer your question about injector duty cycle, yes it's possible for us to add this, but it's not high on our priority list at the moment. First of all, this isn't a parameter inside the DME as the DME doesn't have any knowledge (or care) about duty cycle. Injector duty cycle is something only aftermarket tuners care about because it gives a sense about injector sizing. This is a calculated parameter based on the engine speed and the current opening time of the injector. There are several sources online for this equation and it's also in Greg's books. On our product roadmap, we have the idea of putting "math functions" as a new feature. This would allow tuners to create new "channels" using existing ones along with custom math functions. In the meantime, you'll have to calculate this yourself in Excel after the log is created.

If you're comfortable doing so, you should share what you have so far with regards to your MSS54HP tune so others can learn! Happy tuning! :D
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