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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > SOLVED: N54 Oscillating throttle position/surge at steady speed



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      05-26-2022, 02:48 AM   #45
rsalazart
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Quote:
Originally Posted by Wadger View Post
Good Afternoon All,

Just wanted to drop in a little update.
I have been problem free since my last input, after following the aforementioned procedure. Until now.

I can confidently say this is related to flashing the stock (mhd still installed) map. Or just due to flashing multiple times.
After flashing to the stock map before taking to my local indy for some work, the oscillation was back as previous.
Mostly noticed on slight declines in cruise control and at the same intensity as previous.

Hope this helps others with more knowledge understand the root cause in the software.

Cheers
How many times you switch between maps before the problem back again?
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      06-04-2022, 12:45 PM   #46
Wadger
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Apologies for delayed response.

I only flashed the once since I fixed problem previously.
I just flashed to stage 0 as I know I'd blown a seal in my rear turbo and wanted them to spin as little as possible for the journey to the garage.
But as soon as I got to the motorway on cruise control it was back with the oscillation...
As you can see in earlier posts, nearly everything has been replaced, no boost leaks, holds vacuum as well as pressure..

Reference the post regarding engine codes and reduced power, this must be somthing different entirely.

From my limited experience, I do beleive it is down to the throttle body, now being poorly managed by the DME due to the flashing issue.
I come to this conclusion, at the AFR readings were in reaction to the throttle position variations.
I would rule out wheel speeds sensors, as this would be present regardless of tune or number of times flashed..

Plus it occurs regardless of using cruise control, so that rules out cruise control being the issue. CC just maintains the parameters required to present the issue much better than manual throttle control.

Hope this helps.

Last edited by Wadger; 06-04-2022 at 12:52 PM..
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      06-04-2022, 01:37 PM   #47
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I too am having this issue. It's only at light throttle while at cruising speeds. Under WOT or while running through the gears ot runs great. It's only while driving at a continuous speed.

I may try flashing back to stock and then loading MHD again. Hoping it's not my cam ledges.
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      06-04-2022, 05:56 PM   #48
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Quote:
Originally Posted by Wadger View Post
Good Afternoon All,

Just wanted to drop in a little update.
I have been problem free since my last input, after following the aforementioned procedure. Until now.

I can confidently say this is related to flashing the stock (mhd still installed) map. Or just due to flashing multiple times.
After flashing to the stock map before taking to my local indy for some work, the oscillation was back as previous.
Mostly noticed on slight declines in cruise control and at the same intensity as previous.

Hope this helps others with more knowledge understand the root cause in the software.

Cheers
I don't remember if I publicly stated, but my car has been problem free since doing this too. Thank you again!
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      06-05-2022, 09:53 AM   #49
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It's 100% unrelated to flashing. This is just superstitious nonsense.

All the data im the binary file is checksum protected so if the contents of the flash don't match what was in the data exchange file then the car would not start.

Writing back to stock then writing the OTS maps repeatedly isn't fixing anything. The cause of the oscillations are because of the catalyst and O2 sensor diagnostic routines. I have given the fixes for these problems to Wedge so I expect this will be fixed in the OTS maps in the next revision.

This problem has been discussed in depth on other N54 forums and anyone running a custom tune is able to fix this themselves.
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      06-05-2022, 10:50 AM   #50
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Quote:
Originally Posted by CarAbuser View Post
It's 100% unrelated to flashing. This is just superstitious nonsense.

All the data im the binary file is checksum protected so if the contents of the flash don't match what was in the data exchange file then the car would not start.

Writing back to stock then writing the OTS maps repeatedly isn't fixing anything. The cause of the oscillations are because of the catalyst and O2 sensor diagnostic routines. I have given the fixes for these problems to Wedge so I expect this will be fixed in the OTS maps in the next revision.

This problem has been discussed in depth on other N54 forums and anyone running a custom tune is able to fix this themselves.
Juat wondering do the oscillations occur only on decattted cars and is there a reason why it doesn't occur in every car?

Many thanks for your input and help.
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      06-05-2022, 11:46 AM   #51
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Quote:
Originally Posted by Saif2018 View Post
Juat wondering do the oscillations occur only on decattted cars and is there a reason why it doesn't occur in every car?

Many thanks for your input and help.
Because on decatted cars the diagnosis fails and will keep running.

It can happen on catted cars that have bad O2 sensors or bad cats.

The diagnostic routine manipulates the lamba target and looks for a proportional change in both up and downstream O2 sensors. It also looks at the lag in response along with a change in readings between the up and downstream sensors to work out how healthy the cat is.

These tests only occur at cruising and sometimes idle conditions. Once the engine is put under load they stop.
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      06-05-2022, 12:41 PM   #52
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Quote:
Originally Posted by CarAbuser View Post
Because on decatted cars the diagnosis fails and will keep running.

It can happen on catted cars that have bad O2 sensors or bad cats.

The diagnostic routine manipulates the lamba target and looks for a proportional change in both up and downstream O2 sensors. It also looks at the lag in response along with a change in readings between the up and downstream sensors to work out how healthy the cat is.

These tests only occur at cruising and sometimes idle conditions. Once the engine is put under load they stop.
Many thanks you the explanation.
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      06-05-2022, 05:56 PM   #53
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Quote:
Originally Posted by CarAbuser View Post
Because on decatted cars the diagnosis fails and will keep running.

It can happen on catted cars that have bad O2 sensors or bad cats.

The diagnostic routine manipulates the lamba target and looks for a proportional change in both up and downstream O2 sensors. It also looks at the lag in response along with a change in readings between the up and downstream sensors to work out how healthy the cat is.

These tests only occur at cruising and sometimes idle conditions. Once the engine is put under load they stop.
Thanks for the input, looks like the rest of us were not aware of the test, makes sense

Can you advise the reason this would only present itself on certain occasions?
I assume it always does it, just the severity of the fluctuations change?
For example my issue was only noticeable(but maybe always present to a lesser degree) after flashing to stage 0,however I've experienced it on all stg2, stg2+ and stg0 maps regardless. And the only way I stopped it was doing the full write.

Finally getting hybrids fitted and getting a wedge tune, so this should be covered in the new tune, just interested to understand in a little more depth.

Thanks again for the detailed response, just what I was looking for.
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      06-05-2022, 06:20 PM   #54
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Quote:
Originally Posted by Wadger View Post
Thanks for the input, looks like the rest of us were not aware of the test, makes sense

Can you advise the reason this would only present itself on certain occasions?
I assume it always does it, just the severity of the fluctuations change?
For example my issue was only noticeable(but maybe always present to a lesser degree) after flashing to stage 0,however I've experienced it on all stg2, stg2+ and stg0 maps regardless. And the only way I stopped it was doing the full write.

Finally getting hybrids fitted and getting a wedge tune, so this should be covered in the new tune, just interested to understand in a little more depth.

Thanks again for the detailed response, just what I was looking for.
There's multiple diagnostics that cause it so the severity and conditions of activation will depend on which one is running. They each have different methods of manipulating the lambda.

They do also stop sometimes for a period of time which I assume is related to conditions that inhibit the starting of the routine. Most errors inhibit them and errors can periodically reset.
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