2012 CTSV Maf scaling, open loop issues.

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June 22nd, 2012
ditosmotors

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2012 CTSV Maf scaling, open loop issues.

Im kinda strugling here on what is normally a pretty easy task. Im trying to scale the MAF sensor but puting this thing into closed loop and asking it to command lambda 1.0 doesn't seem to be working. I've done all I can to put it into open loop and set everything up so it will only command lambda 1. The problem I get is the longer this thing runs the richer the fuel mixture gets. When I start logging what the air fuel is at the diffrent MAF points the number keeps changing. When I first check say 3000 hz at idle its reads .98 then after going up through the maf to around 5500 hz and back down to 3000 hz it will now read .88. If I do correct the Maf for that rich of a condition when I put it back into closed loop the fuel trims start correcting for an overly lean condition. The commanded af ratio in the datalogs show commanded 1.0 but there must be something else going on that I'm missing.

The vehicle has LPE heads, GT9 cam, 2.55 pulley, air raid intake, corsa mufflers.
June 27th, 2012
Highlander

Why do you want to do that?

Honestly... tuning these cars in open loop to then go into closed loop is not a good idea... You will never get it exact.
Best thing to do is use STFT and LTFT to do the part throttle tuning... Then do the WOT (open loop) tuning as usual. You will get consistent results and the car will not be bouncing around. After that, apply some math to the curve and refit/redo... It will work out wonderfully.

The GT9 cam is a very simple cam to tune.
June 27th, 2012
ditosmotors

Quote:

Originally Posted by Highlander

Why do you want to do that?

Honestly... tuning these cars in open loop to then go into closed loop is not a good idea... You will never get it exact.
Best thing to do is use STFT and LTFT to do the part throttle tuning... Then do the WOT (open loop) tuning as usual. You will get consistent results and the car will not be bouncing around. After that, apply some math to the curve and refit/redo... It will work out wonderfully.

The GT9 cam is a very simple cam to tune.

I did end up using the fuel trims to get the maf correct. I just wanted too understand why I can't get this thing to run a consistent commanded air fuel ratio in open loop. I didn't know if there were some normalizers I was missing or what. I had tried tuning one of these a while back by putting it into open loop, commanding lambda 1 but after all that work, when I put it back into closed loop the fuel trims corrected positive 25%. So I've been using the fuel trim method since then. I would like to understand why I can't do it the other way. I figured some one out there is using a wide band to tune the idle, part throttle and cruise areas.
June 27th, 2012
Highlander

There are a bunch of tables that need to be changed to 1.0 in order for it to work. There are a couple that are inj temp based and inlet valve temp based... There are quite a few. I've done it, but in the end, you will get Fuel trims in the -7 -8 range if you do it via the wideband. It's not always exact as the sensors have some sort of variation (stock sensors and widebands) between each other. Once in closed loop it appears there are other multipliers making fuel out of whack. Remember we do NOT have access to all the tables. If you do the fuel trim method and then wideband for wide open throttle carefully you should end up with a perfect MAF curve.