I figured out my problem, now how do I fix it? A/F OSCILLATION

[Robbieroflcopter]

Greetings!

For those that have helped with my previous threads. Thank you! I've got the cold start/idle issues resolved. Overall, I'm very happy with how the truck runs now! The one caveat: when at low, steady-state throttle positions (2-8%) the truck will "surge" a little. I've figured out that this is due to the AFR swinging fairly wildly (down to 12, sometimes up to 18). It only does this at this throttle setting. Idle AFR is consistent as are all other throttle positions. After tons of logging, tune changes and a swap to SD I've figured out that it is due to oscillation in my MAF. In those throttle positions the MAF output will swing up and down by 20-30% consistently. More throttle: MAF output is smooth. Less throttle: MAF output is smooth. In SD it runs perfectly at those throttle settings. No I'm not going to run SD just now- I am building a tune for it but there is a bunch of other weird drivability shit I'd have to work on.

My question: Is there a way to smooth or filter the MAF output? Ideally at one throttle setting with no other changes it should be reading the same and not swinging around, correct? I'm running the engine manufacturer's suggested intake and MAF sensor. I'm guessing it is the intake not flowing air smoothly at these throttle settings that causes this? I've also tried other new MAFS and they do the same thing. Is there a way filter these changes, turn down the sample rate or otherwise mollify how sensitive the sensor output is?

Thanks again guys!

[Samboino]

I am by no means an expert, but I've been told by a reputable gen 3 tuner that aftermarket intakes will cause that issue with the MAF reading, he swears by only using the stock airbox if not running SD. My truck had the same surging problem and I went back to a stock airbox and it's much better.

[SiriusC1024]

Tune file and log?

[Alvin]

The intake setup and how the MAF is mounted matters a lot here.

Also if it's got a decent size cam it will do this too. There is nothing you can really do about it. SD makes a better choice for a lot of applications.

[Robbieroflcopter]

Tune file and log?

I'll have to go through them and locate one where I specifically logged this. It's been a while. I've been troubleshooting based on what I saw back then. Everything from thinking it was errant fuel trims to an intake leak. I'm convinced it's due to the MAF signal (it doesn't do it in SD) and will resort to getting one of the honeycomb inserts for the intake if there isn't a software fix. I was hoping there was a way to slow the sample rate down or average the output or something.

[Robbieroflcopter]

That's what I'm thinking. The intake is pretty short and the MAF is mounted just inches from the filter. Here's the intake they recommended: https://www.ebay.com/itm/39490415227...RoC2NoQAvD_BwE

I've been reading alot about this issue with C6 corvettes and apparently the hardware based answer is a honeycomb screen to straighten the airflow. If there isn't a software fix I'll try that I spose.

[Robbieroflcopter]

I am by no means an expert, but I've been told by a reputable gen 3 tuner that aftermarket intakes will cause that issue with the MAF reading, he swears by only using the stock airbox if not running SD. My truck had the same surging problem and I went back to a stock airbox and it's much better.

It's not really possible to go back to the stock airbox here. Intake is in a different spot and rotated or I would have tried that. Also, the new engine is not compatible with my old MAF.

[SiriusC1024]

I've been reading alot about this issue with C6 corvettes and apparently the hardware based answer is a honeycomb screen to straighten the airflow. If there isn't a software fix I'll try that I spose.

Of course there should be a screen. Software solution is SD.

[edcmat-l1]

Intake reversion. You can't tune it out. Only affects the MAF. Run it in speed density. Don't be skeered.

[Robbieroflcopter]

Tune file and log?

So an example of the oscillation in A/F is in the 08312023 log. At the 06:28 mark you can see steady-state throttle with fairly big spikes in A/F change. You don't see that in the other log where I'm running SD. I included my new non-SD tune that I usually run (I'm happy with it except for the oscillation) and my new SD tune that I'm working on (it needs a ton of help for idling for some reason).

[Robbieroflcopter]

Of course there should be a screen. Software solution is SD.

Got a sheet of this, I think I'll stack and align two pieces a couple inches before the MAF.

https://www.ebay.com/itm/15601076566...IAAOSwrzlkHsho

[gtstorey]

My guess is 1/4” honeycomb is too big to do much good. There is honeycomb sold meant for this use and it’s a lot smaller.

[edcmat-l1]

The honeycomb in MAF sensors were designed to straighten the air ENTERING the MAF. They weren't designed or meant to prevent reversion.

[Robbieroflcopter]

My guess is 1/4? honeycomb is too big to do much good. There is honeycomb sold meant for this use and it?s a lot smaller.

I saw that they sell some slightly smaller stuff (3/16) but I figured if I do a full inch of this prior to the MAF it should have the air fairly well sorted out. I'm guessing it's not going to take too much based on how close the MAF is to the filter. It's probably swirling all over in that tube after it has just left the much larger filter area. We'll see I guess.

[Alvin]

I had a piece of screen someone added to a tube come loose and lodge into the throttle body on a procharged C7 when those cars were new.

Sat on the rev limiter while I held the ignition button to turn the car off. However many seconds it takes to shut down felt like eternity.

[SiriusC1024]

The MAF signal looks rough. Another thing is the fuel trims are pretty far off. Later in the log CL-Fault. This doesn't happen in SD?

[Robbieroflcopter]

The MAF signal looks rough. Another thing is the fuel trims are pretty far off. Later in the log CL-Fault. This doesn't happen in SD?

Nope, the A/F is rock solid in SD at those same throttle positions. Almost always stays with a point. As opposed to 4 or 5 point swings with the MAF turned on. The fuel trims try and correct for the MAF as it does the oscillation thing. They swing wildly. Initially I thought the fuel trim was the problem so I disabled closed loop and it still did it.

[edcmat-l1]

The MAF signal looks rough. Another thing is the fuel trims are pretty far off. Later in the log CL-Fault. This doesn't happen in SD?

The rough MAF signal you're seeing is the sensor reacting to the air going in different directions. There's nothing wrong with the sensor. It's reporting exactly what it's seeing.

[SiriusC1024]

The rough MAF signal you're seeing is the sensor reacting to the air going in different directions. There's nothing wrong with the sensor. It's reporting exactly what it's seeing.

That's right, and it was what I was getting at. Seems to me as evidence that a screen will probably help. Reversion shouldn't be happening up above 1200rpm, yet the signal is still rough.

[SiriusC1024]

Nope, the A/F is rock solid in SD at those same throttle positions. Almost always stays with a point. As opposed to 4 or 5 point swings with the MAF turned on. The fuel trims try and correct for the MAF as it does the oscillation thing. They swing wildly. Initially I thought the fuel trim was the problem so I disabled closed loop and it still did it.

Is there a reason you don't want SD? It'd be so much simpler.