[Knifeedge2k1]

**Cross posting this from the F30 forum that I posted into (My care is actually a G30 520i but given this isn't available in the US I figure it would get more eyeballs here.)


Hi Guys,

Firstly I apologize for the wall of text but it's just how I write.

I've just noticed something strange throttle action while logging pulls done into higher gears (4th and higher).

Background:
Car: G30 5 Series
Year: 2019
Trim: 520i MSport
Engine: B48B20B (identical to 30i engine hardware-wise, difference in software)
Fuel: 98 RON (93 AKI), no E85 or any form of ethanol where I live
Mods: Only JB4, stock everything else

Originally I was intending to increase my boost via the JB4 given the artificially low limits set in the stock ECU tune from the factory. Given the gains available from a proper flash tune on the 20i engines I didn't feel Map 3 on the JB4 was "enough" so I was just getting some data to see how much more additive boost I could command safely.

While gathering data however, I noticed that my engine was experiencing extreme amount of forced throttling at speeds greater than 90mph in 4th and 5th gear (I presume it would be true in 6th-8th as well but given I don't have the space nor power to pull in those gears so it's a bit of a moot point).

All my prior logs/pulls in 2nd & 3rd gear from 2200rpm-redline have had throttle progressively ramp up to 100% and stay there. Once in 4th or 5th however at ~5000rpm I can see the throttle cut back extremely abruptly and the throttle oscillating/feathering in a strange manner (while on JB4 maps 1 thru 3) and all of this is accompanied by a drop in DME BT (comparing the DME BT at the same RPM in 4th vs 3rd for example always yields a lower DME BT in 4th vs 3rd).

Its worth nothing that as far as I can tell, this throttling is NOT accompanied by a drop in timing or AFR straying too lean so is not obviously "safety" related behavior in my view.

At first I thought the throttling was caused by something that happened "around" the gearshift which I couldn't see in the logs.

So I proceeded to do a single gear pull in 4th and 5th to see if the same problem occurred .... and it did.

Curious

I then proceeded to see if maybe the JB4 was doing something strange so I tried to do a few runs in Map0 (JB4 is "off") ... and STILL I see this forced throttling.

With the data from the Map 0 log though it seems "obvious" to me that this behavior is hardcoded into the 20i ECU (or atleast ... it's hardcoded into MY 20i ECU).

My only guess is that as part of the detuning tricks used to downspec the 30i engine to what we have in the 20i. It seems there's a combination of forced throttling & DME BT reduction triggered by high speed (90+MPH and or a combination of RPM & gear trigger .... i.e Gears 4 to 8 and RPMs in excess of 4500 to 5000rpm or something).

I have NOT seen this throttling action happen on any B58 or B48 (30i) logs I've seen, but to be fair, there aren't THAT many logs which have useful data beyond 90MPH as most people log on their draggy runs where they don't really push beyond the 1/4 mile or on the street where it will be difficult to push up to 120+mph safely.

It would be interesting to see if other 20i owners that are still on stock ECU (not flashed) can corroborate my results above. If a few users experience the same thing then unfortunately the conclusion would be that the JB4 is basically useless at 90mph+ on a stock tune 20i engine as the throttling action seems to be hard wired into the ECU. A flash tune like MHD or BM3 should get rid of this behavior (but again I'm not certain as I have not seen many BM3 or MHD logs myself with significant data above 90 MPH). With that said I am still glad I got the JB4 as it's "undetectability" during warranty period means it's the only thing I can do at the moment plus it still has good logging features and even out of warrant when I will eventually get a BM3 or MGF tune or something the JB4 can still act as an effective boost controller and/or WMI controller down the line.


I'll try to get these logs into a chart form in the next couple days so I can explain the above visually but I really wanted to get this out there first since I've been racking my head around this throttling thing for a few days now.


Photos

You can see the Map3 throttle goes nuts in 4th and 5th gear but in 3rd gear it progressively builds to 100 and stays there. In Map0 the throttle closes but doesn't feather/flutter/fluctuate/oscilate as much (no doubt because the JB4 spoofing is causing some type of feedback loop which isn't happening on Map0). In either case the throttle closure occurs BEFORE any overboost condition (defined as ECU PSI > DME BT) takes place so the throttle response in this case cannot be a response to overboost condition. The throttle closure also happens without any drops in timing, AFR deviations, trim deviations, FuelPressure High deviations, or anything else I can think of.