Short term fuel trim swings

Hi,

First of all, great courses and content! I have a Bmw e46 turbo build that is following me along this course. Today I took the car for a couple of quick log runs to evaluate the fuel trims and I can see that the STFT "swings" during the RPM run. I'm wondering if this amount of swing trim is resonable? I have attached a graph from MegaLogViewerHD.

I remember Andre saying that "ecu will swing the AFR for effective catalytic converter operation". In my case the delta of the swing is around 6-11%. It also logged one peak of +19% trim which looks a bit odd. During idle the trims are within +/- 5%.

Some background on the setup

- Chargepipe is not connected (breathing atmo)

- Stock injectors + stock fuel maps

- Audi RS4 MAF using correct diameter piping, scaled to values from MS4X wiki

- GTS450 fuel pump with external FPR adjusted to stock base pressure of 3.5 bar

- Single stock o2 sensor in downpipe (probably really old...)

- Cat delete

- Long term fuel trims disabled

- Individual cylinder trims disabled

I want to get to grips with these trims before I install the larger injectors, or else I will be in the unadvisable position where I have both changed the MAF and the injectors. I have ordered a new o2 sensor for my peace of mind, it can be well over its lifespan and I dont want to question it in the future.

Thanks for any inputs :)

Edit: I did apply left foot breaking for all but the end in this log.

That all looks quite erratic. I'd try narrowing things down by stopping fuel trimming to see if injector pulse is still erratic due to airflow being erratic, and then dive into the root cause. If your fuel on time is being calculated based on erratic airflow values, your injector time and fuel trims are going to be erratic as well.

Thanks Mike! MAF was the problem. Voltage output was somehow way to high, calculated load was off the map axis because of this. Swapped it toady and just form a quick look at live data it now seems to be sorted.