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Technical Topics B48 4-Cylinder Turbo Engine / Drivetrain / Exhaust Modifications Forced throttle closure on 20i engine

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      10-04-2020, 06:51 AM   #1
Knifeedge2k1
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Forced throttle closure on 20i engine

**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.
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      10-04-2020, 04:33 PM   #2
Don76
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I'm running a 2020 320i B48.
It's stage 2 mapped (BM3) with decat downpipe, MST intake and OPF + Res delete mid section.

It's fierce in gears 1 through 4, but after that it really lacks decent pull. Obviously by this point I'm above speed limits and so not a major issue - but I'd love to know if my car behaves like your description ref throttle closing.
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      10-04-2020, 07:22 PM   #3
Knifeedge2k1
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Quote:
Originally Posted by Don76 View Post
I'm running a 2020 320i B48.
It's stage 2 mapped (BM3) with decat downpipe, MST intake and OPF + Res delete mid section.

It's fierce in gears 1 through 4, but after that it really lacks decent pull. Obviously by this point I'm above speed limits and so not a major issue - but I'd love to know if my car behaves like your description ref throttle closing.
Given you've flashed your ecu I doubt you experience the same issue

Having a stock 20i or stock + tuner box (as opposed to flashing ecu) to compare would be the way to verify my diagnosis.

The reason you lose pull in higher gears is of course because of the non linear power requirements of overcoming air resistance. I've actually built up a spreadsheet that can quite accurately predict performance (real life acceleration) vs wheel dyno figures. Would post if anyone is interested
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      10-04-2020, 10:33 PM   #4
VipinLJ
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I was just reading your post on n54tech! I had no idea you were on here too! Huge shout-out for all the help on n54tech!!!

Mine doesn't have closures like yours does, in any gear. So looks like it is a 20i vs 30i issue.
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      10-05-2020, 05:07 AM   #5
Knifeedge2k1
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Yea it seems to be a 20i thing

Would be great to see if any 320i owners are exoskeleton the same issue
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      10-05-2020, 07:18 AM   #6
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Here is mine 320i @ map3
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      10-05-2020, 08:41 AM   #7
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Quote:
Originally Posted by AlexxZeman View Post
Here is mine 320i @ map3
Yea you seem to be experiencing the same thing (Care to attach your CSV for more detail?)

Btw you should display your dme bt and boost2, boost1 is basically useless.
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      10-05-2020, 07:12 PM   #8
Knifeedge2k1
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Looks like there's something wrong with that data... That ecu psi number is crazy
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      10-06-2020, 02:13 AM   #9
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Quote:
Originally Posted by Knifeedge2k1 View Post
Looks like there's something wrong with that data... That ecu psi number is crazy
Yes, looks like that. I'll update to latest firmware and will do a new log.
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      10-06-2020, 05:25 AM   #10
Knifeedge2k1
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Coolio

Stay safe though

Not easy to be able to run up to 135mph
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      10-14-2020, 11:42 PM   #11
Knifeedge2k1
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Bump

Anyone running a JB4 with stock ECU flash on a 20i platform ?

If so can you please share your logs from a 4th gear (or higher) pull ?
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      11-10-2020, 02:02 AM   #12
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Quote:
Originally Posted by Knifeedge2k1 View Post
Bump

Anyone running a JB4 with stock ECU flash on a 20i platform ?

If so can you please share your logs from a 4th gear (or higher) pull ?
Don't have a chance to test 4th+ gears yet, but here is my logs for stock vs map1. As I understand there is a throttle downforce.
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      11-19-2020, 09:49 PM   #13
Knifeedge2k1
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I have a feeling yours is octane related

Mine doesn't throttle like that even in map 0

Or maybe it is accelerating WOT from a standstill thing
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      04-27-2021, 07:19 AM   #14
Knifeedge2k1
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Yeah I need to change my answer, my car DOES pull throttle even in map 0 now.

Timing keeps climbing so it's not octane/ping/pre-ig related.

I think it's just a weird hardwired thing in 20i engines.
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