AFR going rich post shift - N54 DCT

Asbjorn

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So ever since I started tuning my car with GC lites and BQ, I have had an issue where either bank #1, #2 or both goes rich post shift. So instead of having an afr of 11.x, it goes to 10.x. Whichever bank is doing it sees a flat lining STFT. It never happens if I just do a 3rd gear WOT pull. It only happens post shift. Sometimes the rail pressure even drops to around 1500psi as seen here:

https://datazap.me/u/asbjoern/22b-competition-water-injection-6?log=1&data=3-20-21

Here's a continuous log with some examples of the riching out post shift.



The problem with this is that it causes power to hesitate slightly, and if I do 20 pulls on track, maybe 1 or 2 of them will also feel like the car misfires post shift. No codes though. I typically lift off immediately when I feel something is not right. My tuner says a bank going too rich can cause misfires.

I have pulled the plugs, and they looked fine, so leaky injectors are ruled out. Adaptations have been reset many times. Injectors are as old as the GC lites and are index 12. Same with primary O2 sensors. The secondary O2s were swapped earlier this year and did not change anything. The HPFP was replaced under warranty eight years ago. The LFPF I replaced last year (OEM Z4). The post shift stft flatlining was there both before and after the LFPF replacement. I have never done a leak-down test on the engine, but the cylinder pressures have been tested a month ago or so, and looked fine. This is the last comment I have gotten from my tuner three weeks ago ago:

"Something causing you bank to go rich, so the o2 senors (both banks) comes to mind now"

Could it really be that the primary O2 sensors have been bad from when they were installed from new two years ago?

Could a boost leak after the tmap be causing it?
 

doublespaces

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This one shows Bank 1 going lean for a moment, perhaps confirming the misfire you're feeling which is sending uncombusted air across the O2 sensor.
31757


Do you have the M-Boost MHD upgrade? Perhaps ask BQ if he can help you tune around this issue, it may help you isolate the problem.
 

Asbjorn

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Yes I have M boost. This issue was there both before and after swapping tmap and buying M boost.

Thanks for pointing out the afr peak, I will try and find it and send it to my tuner. But basically he wants me to replace o2 sensors if a reset doesn't do the trick. I have seen logs from two other Z4 dct customers of his, and they dont have this issue it seems. I would just have thought that if bad o2s causes flatlining stft post shift, that it was well know already. Maybe it is a dct thing...
 

Asbjorn

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Replaced both primary O2 sensors, and replaced all the old index 12 injectors with new ones. The problem is still there every second or third log, and is on-off post shift. Here's alog that looks okay

 

Asbjorn

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Here's a log where one of the banks go rich post shift. Sometimes it happens on bank one, sometimes on bank two, sometimes on both. Post shift it may stay rich for some time, then come back to normal. Then I do another shift, and it might happen again. Sometimes it takes two WOT shifts before it happens. Turning WI on or off doesn't seem to make a difference. My tuner says I need to check my DME injector mosfets, but Im pretty sure that a burned mosfet would fail all of the time.

 

doublespaces

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Have you considered trying another tuner since this seems to happen when you switched? It's probably a lot cheaper to rule that out than replace hard parts over and over. There's a lot of good tuners but they ALL make mistakes or have unexplainable things happen for which they can only blame your car.
 

Asbjorn

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Have you considered trying another tuner since this seems to happen when you switched? It's probably a lot cheaper to rule that out than replace hard parts over and over. There's a lot of good tuners but they ALL make mistakes or have unexplainable things happen for which they can only blame your car.

At this point there aren't really any hardware left to swap. I have 100% confidence in BQ though. If it is indeed a tuning issue we will find out. The few times he has been wrong, we have learned together. Like he said DCIs would be better for my car, and logging showed they weren't. Most people would have made that "mistake" imho.
 

Asbjorn

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Just did a log on stock map as well. Here we see the same problem with stft flatlining post shift on stock map. My next step of action is to replace the dme injector mosfets (MSD81). And just to confirm. If I start in 2nd, it happens when shifting to 3rd. If I start in 3rd it happens when shifting into 4th. It doesn't happen each time, and it is not isolated to one bank, and it is on then off.



Any alternative suggestions would be highly appreciated. Already USD 2000 deep into this repair... :sweatsmile: @RSL @R.G. @V8bait @Chris@VargasTurboTech @jyamona
 

RSL

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I've seen post shift flat line trims like that on mine before, but never on a stock rom and primarily from cat protect. Temps seemed to effect mine, more likely to hit it when it was hot. I assume it was environmental offsets.

Yours goes super rich on the tuned rom when it stops trimming because the 20-25% it was pulling goes to 0% when it stops and all that extra fuel is no longer removed. That might be separately causing an issue after the fact.

Might keep the stock rom in, reset adaptations on it and see if anything clears up/comes back over the next couple of days/pulls. It sure looks like you might have a lazy injector in bank 1 though, after the swap. Bank 1 takes its time to full lean off the pedal on both the tuned and stock roms.

You've got a least a year on those cats now, right? Have you inspected them since they went back in?
 
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Asbjorn

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I've seen post shift flat line trims like that on mine before, but never on a stock rom and primarily from cat protect. Temps seemed to effect mine, more likely to hit it when it was hot. I assume it was environmental offsets.

Yours goes super rich on the tuned rom when it stops trimming because the 20-25% it was pulling goes to 0% when it stops and all that extra fuel is no longer removed. That might be separately causing an issue after the fact.

Might keep the stock rom in, reset adaptations on it and see if anything clears up/comes back over the next couple of days/pulls. It sure looks like you might have a lazy injector in bank 1 though, after the swap. Bank 1 takes its time to full lean off the pedal on both the tuned and stock roms.

You've got a least a year on those cats now, right? Have you inspected them since they went back in?

Awesome inputs as always. This got me researching:

Regarding the warm vs cold theory: Did six logs today: First two were ok, then third and fourth were not, then fifth were ok, then sixth were not. So no correlation between hot and cold. But typically the car is OK during the first two logs after a good reset. This was true both before and after the injector and o2 sensor change.

Regaring the down-pipe theory, then the problem was there also with the stock down-pipes, and when they were fairly new. I bought at set of new OEM down pipes last year and have logs that show the same problem. Now running 200cell hi-flow down-pipes.

Here both banks stft go zero post shift with old injectors and WI

Here it does the same, both banks, with 6 new injectors and WI

I have never seen both banks flat-line without WI.

Those logs are all with WI, and afr on both banks returns to 234 very slowly. Same here on map 22c (three logs with WI). Sometimes 1 is faster, sometimes 2 is faster:

Then with no WI on the same day, afr on bank 2 returns to 234 much quicker. Bank 1 never returns to 234 (three logs):

Same on stock map with no WI with new injectors and o2 sensors:

Then did a complete reset of all adaptations except batteri today, no WI, afr on bank 1 never returns to 234, stft only flatlines on bank 1 post shift and only 50% of the time:

Now back to the old injectors and o2 sensors, here's how afr returned with a short burst of WI, both banks are slow to return,

Here's how afr returned without WI on same HW, same day, both banks return fairly quickly.

With the new hardware, I cannot get bank 1 afr to return to 234 no matter how I lift off the throttle on stock map, no matter which gear, down hill or up hill. Here is one example:

I am also realizing that on stock map, I can only get bank 1 to go zero post shift. Done 10 logs, and it always happens on bank 1. With 22c and WI, it happens on both banks:

https://datazap.me/u/asbjoern/22c-competition-wi?log=0&data=3-13-14-21-23-24 (bank 2)
https://datazap.me/u/asbjoern/22c-competition-wi?log=2&data=3-21-23-24 (bank 1)

With 22c and no WI, I only have one log where stft flatlines on bank 2, while afr returns to 234 on bank 2, but never on bank 1:
https://datazap.me/u/asbjoern/22c-competition-no-wi?log=0&data=3-21-23-24

On high boost map, stft flatlining causes rich condition, on stock map it causes lean condition, so not sure if injector leak can explain both, but it does look like the new injectors on bank 1-3 might be leaking more than the old, in which case I need to try and return them.

TL;DR / Summary: Done 10 or so logs on stock map with no WI. (Edit: just did 4 more). Flatlining only seems to ever happen on bank 1 with stock map. Also afr never returns to 234 on bank 1, no matter what I do, or which map I run with the new injectors. With high boost, both banks sometimes flatline seperately post shift with the new injectors. Them flatlining together only happens with WI.
 
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RSL

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I forgot you added WI. I've never used it, but it would obviously be another potential source. Do you spray straight through shifts? If you're spraying in the IC, there's a delay between shutting off and water left in the intake tract making it to the cylinders.

Increased burble/overrun might cause AFR slow to return after letting off. Have you changed any of those settings?

There may be multiple things going on that produce somewhat similar effects. At least for diagnosing, I'd leave stock rom and WI off to eliminate tune/WI as sources.

If you installed remanned injectors for the swap and still have the old bank 2 injectors laying around, might consider tossing those in bank 1 to test since they seem like known good injectors.
 

Asbjorn

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So a quick update on my issue where stfts would sometimes flatline post shift, causing either rich or lean afr depending on map.

First of all, it turned out @RSL was right - one of the brand new index 12 injectors I installed was indeed lazy.

After reinstalling one of the old index 12s in cyl 1, the afrs now have no problem returning to 234 on lift off. For once I was lucky and only had to touch one injector.

As for the stfts flatlining post shift - we never learned what caused the problem. Only that WI makes it worse.

It wasn't injector related.
It wasn't o2 sensor related.
It wasn't fuel mode related.
We didn't find anything wrong with the DME.
Doing a complete and full reflash as well as adaptations reset wasn't a permanent solution either.

After doing all the HW-related "repairs", the issue would still happen on bank 1 with MHD stage 0, and on bank 2 with the old BQ map. As the problem existed with the MHD map, I contacted them, and they confirmed they had never seen the issue before. Their tuner did comment that I might have a tuning related issue causing the fuel mode to change post shift. This was however never confirmed.

So I have agreed with my tuner to work around the problem in the tune instead. This means BQ is tuning the stfts to sit closer to zero. So if they flatline post shift in the future, they won't cause too rich/lean a condition.

Below is the latest map revision, and BQ is still working on fine-tuning the map. The main challenge with this solution is that stfts are dependent on many factors, and I might end up having to run different maps depending on the season. Time will tell.

So although we never found the root cause for my stfts flatlining post shift, I am marking the issue as solved through tuning. A huge thanks to @RSL for the help and support through PMs.

 

carabuser

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Have you tried logging the Fuel Mode and Torque Limit channels? They can be useful in narrowing down issues like this on a DCT.

If you want a Z4 DCT log to compare values to this is my latest, this is just a custom map: https://datazap.me/u/rich/v124

One observation of those logs you posted is that the wastegate PID looks quite unstable. Your WGDC after PID is all over the place.
 

Asbjorn

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Have you tried logging the Fuel Mode and Torque Limit channels? They can be useful in narrowing down issues like this on a DCT.

If you want a Z4 DCT log to compare values to this is my latest, this is just a custom map: https://datazap.me/u/rich/v124

One observation of those logs you posted is that the wastegate PID looks quite unstable. Your WGDC after PID is all over the place.

Both fuel mode and tq limiter channels can be selected in the log above. Normally I log both, unless I turn dsc off and need an extra channel. Here's a clean 3rd gear log.

 

carabuser

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de and tq limiter channels can be selected in the log above. Normally I log both, unless I turn dsc off and need an extra channel. Here's a clean 3rd gear log.

That log looks much better.
Do you not have any logs of the problem occurring with those channels selected?
 

carabuser

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It hasn't happened yet on the latest maps. Here's an older one with the channels you mentioned.


I really expected to see fuel mode 6 pop up but everything looks OK.

There's all sorts of convoluted tables relating to cat regeneration and preservation in the DME. I spent the last 2 days going back through the old MSD80 damos looking for useful tables and I was shocked at how much of it is devoted to background diagnostic tasks.
 
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Asbjorn

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I really expected to see fuel mode 6 pop up but everything looks OK.

There's all sorts of convoluted tables relating to cat regeneration and preservation in the DME. I spent the last 2 days going back through the old MSD80 damos looking for useful tables and I was shocked at how much of it is devoted to background diagnostic tasks.

I did see mode 6 on the stg 0 map, but never on the BQ maps.