OL for idle to compensate for reading rich with long tubes?

[turabo87]

Just finished tuning a 2018 Camaro SS for cold air intake and offroad long tube headers. Came out fantastic except for one thing I'm not happy about: STFT's reading about roughly about 10% rich around idle and light cruising (10% for MAF frequency by idle area and tapers to less than 2% for high load areas). I KNOW this is not accurate because of the long tubes and because that area of the MAF curve, those values are still stock while my mods are all increasing airflow and fuel demands, so I know for a FACT it's not rich. Anyway, problem is because the O2s falsely read rich, they're trimming about 10% fuel out and I feel a slight idle misfire every couple of seconds.

Was wondering from other experienced folks if my best bet might be just forcing idle to OL by forcing it to PE mode with 0% Pedal and 0%torque for that idle RPM with a PE target of 1.000. I've never had to resort to this on other tunes but contemplating it now (usually I compensate for this issue with changing the O2 switching voltages to 500mv instead of 450mv and works well, but not working well for this time.)

Or maybe there's a better solution?

[Ben Charles]

Why not dial in the airflow model??

[turabo87]

Airflow model as in VVE model or MAF curve? As in disable MAF, dial in VVE below 2-3k RPM? If it's MAF curve, I typically use the STFT %error method from primary O2s to reshape it. I did this (removed about 10% depending on area of MAF curve based on the STFT error recorded) and engine felt worse, which makes sense from an airflow perspective it was never rich. It was falsely reading rich from the long tubes.

[TriPinTaZ]

First, the cold air intake itself changes what the MAF reports to the ECU. So stock values are incorrect. The MAF needs to be rescaled to account for the cold air intake. Second, your O2's are now further downstream and the tune needs to be adjusted to account for the O2's being further away from the exhaust ports. Third, without a wideband nothing you have claimed to be fact is indeed fact. These changes are very simple to tune for and you do not need to rethink the wheel. You need to follow the tried and true guidelines.......that may vaguely exist by reading a lot of information on this forum.

[turabo87]

Ahh a fellow SF tuner! Absolutely agree with your thought process and comments. I rescale MAFs all the time, with narrow band data as well as wideband depending on application and accuracy of the sensors. However my (limited) experience with LT Camaro MAF curves has been so far consistent that the factory MAF curves are rich from factory, so I'm not surprised with the tight STFS's in the higher MAF values/higher airflow.

Apart from the slight switching voltage correction (500mv instead of 450mv), I don't see how much more I can "adjust the the tune to account for O2's being further away from exhaust ports". Narrow bands are design to read stoich and small deviations from stoich, so it's not like I can change the O2 switching voltage to a much higher value.

[Ben Charles]

Transport delay is a good start….

[turabo87]

Thanks Ben, will look into Transport delay.

[Dominatorstang]

https://forum.hptuners.com/showthrea...at-and-Catless

Changes made for long tube headers
Engine>Fuel>Oxygen Sensors>Integral Delay>Airflow Mode - bump up 15% for O2 sensors moving downstream a little

For me it was the above.

[turabo87]

https://forum.hptuners.com/showthrea...at-and-Catless



For me it was the above.

Thank you. Gonna give it a try.

[TriPinTaZ]

It doesn't hurt to reduce Proportional Airflow Mode 10-15% in addition to the Integral Delay.

Also keep in mind, MAF changes/rescaling is no longer JUST MAF changes. This changes torque calculations as well.

[turabo87]

Talking about transport delay settings, in your experiences what's a good data driven method to dial in delay? Assuming I have a wideband and can datalog the AFR swings, how can this be approached without just randomly subtracting the values? What about O2 switching points?

Case in point: Dialed in a Heads Cam NA C7 in Open loop for VVE and MAF, absolutely dialed in the AFR and rock solid with no swings. As soon as I turned on STFT's, the AFR was swinging pretty aggressively between stoich and lean 16-17AFR. I tried reducing the delay voltages by 5-10% and didn't notice much difference on the AFR swinging. Tried changing O2 lean/rich switching points to 500mv instead of 450mv, not much of an improvement either. Slight improvement but drivability still nowhere near as good as with OL. I've never had success with closed loop with big cam cars with long tubes.