AFR Oscillation -30 to +30 STFT when <5% throttle

[Dyyd]

I've been troubleshooting the same issue, here is a log of mine, I get a jerk on light throttle when the afrs spike from 14 to 19+

datazap.me | Surge1989 | Log 1708961582

datazap.me

I have a thread about it on another forum, guys are suggesting: clean vanos solenoids, walnut blast, new LP sensor, clean throttle body and tmap sensor so on and so forth

Sorry, I somehow managed to miss that you posted a log. Yes as carabuser mentioned this is a different issue.

Looking at the log, it is a 10 second log and the throttle is being pumped 5 times from 0 to 16. Is this intentional to induce the jerk? What happens if throttle is kept steady?

It seems your load req. goes up with time, even though throttle is relatively still. Looks tune related, as carabuser asked, does this happen on stock tune?

 

[surge89]

Reason I chimed in is if you look at his logs when his stfts go to 30 he also gets an afr spike and I seem to be getting the same thing stfts from -30 to +30 and then an afr spike from 14 to 21, on my car it causes a jerking sensation

My car has been doing it since stock with the cats...

 

[surge89]

Sorry, I somehow managed to miss that you posted a log. Yes as carabuser mentioned this is a different issue.

Looking at the log, it is a 10 second log and the throttle is being pumped 5 times from 0 to 16. Is this intentional to induce the jerk? What happens if throttle is kept steady?

It seems your load req. goes up with time, even though throttle is relatively still. Looks tune related, as carabuser asked, does this happen on stock tune?

Sorry I just saw your post, yeah the pumping is me trying to see if I can avoid the jerk by playing with the throttle and some of it is me inducing the jerk just to see the spike, Previous owner said he had same thing on the stock tune but now Im doubting it was the stock tune so I'll flash it when I finish the m3 rear end and report back

 

[mj6234]

I think you two have completely different issues, I don't see any commonality in the logs at all. Both are likely software related though.
When tuning catless cars I now make corrections to the exhaust pressure tables to reflect the lack of restriction in the primaries and also adjust the diagnostic routines such that they pass the catalyst checks, rather than crudely just disabling them. I also disable the catalyst heating and ageing functions.

Interesting. On higher boost cars (upgraded twins/single turbos), do you recommend rescaling those tables? Seems like if you have twins and are running 28psi, there could be 40psi+ of pressure at the O2 sensor. The stock scaling only seems to go up to 8psi or whatever. If I understand right, the higher the pressure in the exhaust skews the reading away from stoich, so could get overly rich readings - which is dangerous.

 

[carabuser]

Interesting. On higher boost cars (upgraded twins/single turbos), do you recommend rescaling those tables? Seems like if you have twins and are running 28psi, there could be 40psi+ of pressure at the O2 sensor. The stock scaling only seems to go up to 8psi or whatever. If I understand right, the higher the pressure in the exhaust skews the reading away from stoich, so could get overly rich readings - which is dangerous.

At 28psi you're already well outside of the realms of a well calibrated tune since you'd have boost scaling being involved and that means almost every single table in the DME will be inaccurate.

The public XDF only has a tiny amount of tables defined, but with boost scaling, any table that references torque, load, airflow, fuel mass, manifold or exhaust pressure will be wrong, and that's probably 50% of them.

 

[mj6234]

But even for stock turbo cars that run 20psi with stock load tables it seems like the skew could be a real issue.

I looked around and we use a LSU 4.9 sensor. I didnt look too hard for the actual data sheet, but found this that shows the pressure skew. Stock on the rich side is 0.905 compensation at 8.2psi.

The below chart shows something like 10.5% skew at 1.6 bar absolute on the rich end.

But at 15psi (2 bar absolute) it is more like 15%. At 22psi (2.5 bar absolute) seems like it would be at least 20%.

Wondering if people have been running leaner than thought and getting away with it (or maybe sometimes not).

Bosch LSU 4 Information

EDIT
Maybe it isnt as bad as I thought.

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