Calibrating MAF

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zaclaw
Posts: 42
Joined: June 9th, 2017, 9:29 pm
Location: South Carolina, United States

Calibrating MAF

Post by zaclaw »

I just installed a new exhaust and deleted the rear converter. The stock downpipe is still there but the front converter is hollow. I desperately need to get my MAF calibrated. Fuel trims were a little off before, but now the difference is much more significant. I've spent time reading through guides but some things seem a little unclear, such as plotting the data for the MAF intervals to align with the scale in VT. Any assistance would be appreciated. I attached logs (.csv) and the tune I am currently using.

Current mods are in my signature. Currently my BPV is set to full recirculation to avoid rich spikes during logging. BCS DC is zeroed out, running spring pressure only. I'm not looking to get it perfect necessarily the first time, just to get it more safe and accurate.

https://www.dropbox.com/s/whecy1ic65s7u ... 9.zip?dl=0
https://www.dropbox.com/s/bz6r3jz2zk4t0 ... vtune?dl=0
2007 Mazda CX-7 AWD Grand Touring - Electric Blue Mica
CST4 turbo, CS 3.5bar MAP, CS Stage II SRI w/ TIP, dual port BOV/BPV, 3 port EBCS, 3" TBE w/ Magnaflow muffler, KYB Excel-G shocks, deleted catalytic converters
Disabled EGR, 2nd O2, VTCS
mituc
VersaTuner guru
Posts: 1324
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: Calibrating MAF

Post by mituc »

It doesn't matter what you do on the exhaust side as long as you did not damage the primary O2 sensor. If everything is sealed properly and all the sensors are working fine, as long as you do not change the MAF housing it doesn't matter what you do to the car: change exhaust, change TMIC, change turbo, and so on.
How the engine may draw unmettered air or maybe there's an exhaust leak before the primary O2 sensor which would also explain why the ECU keeps adding fuel in your case, especially in the last two partitions of the LTFT tables (>50g/s).
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
zaclaw
Posts: 42
Joined: June 9th, 2017, 9:29 pm
Location: South Carolina, United States

Re: Calibrating MAF

Post by zaclaw »

Ok thanks for the input. I didn’t hear anything indicative of an exhaust leak prior to the 3” install. The stock downpipe is still installed because I cannot find a 3” for the CX-7. I’m going to get it on the lift tomorrow and check for exhaust leaks before the primary sensor just in case. I was able to compile the data for a coarse calibration using STFT+LTFT calculations, but the slope on the graph is not much different from the last calibration. Which makes some sense I guess, having a stock-sized MAF housing. With the calibration flashed, fuel trims do seem a bit more stable but still have spikes under load.
2007 Mazda CX-7 AWD Grand Touring - Electric Blue Mica
CST4 turbo, CS 3.5bar MAP, CS Stage II SRI w/ TIP, dual port BOV/BPV, 3 port EBCS, 3" TBE w/ Magnaflow muffler, KYB Excel-G shocks, deleted catalytic converters
Disabled EGR, 2nd O2, VTCS
zaclaw
Posts: 42
Joined: June 9th, 2017, 9:29 pm
Location: South Carolina, United States

Calibrating MAF

Post by zaclaw »

Thanks, I did find a leak at the TIP. The clamps on the turbo were loose. Tightened them up but still saw over 20% STFT. Took a log Saturday, I’ll post here shortly. It appears that the high STFT occurs around the open loop transition point of 1.25 load. There was one occurrence where it trimmed high but did not hit 1.25, but close, like 1.222. I had flashed some changes to the tune and only had about 40 miles or so on it. AFRs were mostly close to target. It was adding fuel in some areas with higher load when AFR was already richer than commanded.

I’m a little unclear what the logic is behind how the ECU uses STFT and LTFT. I always thought STFT is used for closed loop and LTFT is used for open loop. I understand the STFT are still visible even if not used in open loop. What does the ECU do when transitioning to open loop and LTFTs are not yet learned?

I put a lot more miles on this same flash yesterday and with my WiFi OBD2 and Torque app I was seeing live data where the fuel trims looked quite good. No STFT spikes, low LTFTs. Dual Port BOV/BPV is causing -25% when letting off accelerator. Yesterday’s observations may not be accurate due to the resolution of the PID wirelessly (cheap adapter) so I will log with VT.
2007 Mazda CX-7 AWD Grand Touring - Electric Blue Mica
CST4 turbo, CS 3.5bar MAP, CS Stage II SRI w/ TIP, dual port BOV/BPV, 3 port EBCS, 3" TBE w/ Magnaflow muffler, KYB Excel-G shocks, deleted catalytic converters
Disabled EGR, 2nd O2, VTCS
mituc
VersaTuner guru
Posts: 1324
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: Calibrating MAF

Post by mituc »

Every time after you fix a leak either reflash your tune or disconnect the battery negative terminal to reset all the fuel trims learned while the problem was there.

Take a log and we will look at it.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
zaclaw
Posts: 42
Joined: June 9th, 2017, 9:29 pm
Location: South Carolina, United States

Re: Calibrating MAF

Post by zaclaw »

mituc wrote:Every time after you fix a leak either reflash your tune or disconnect the battery negative terminal to reset all the fuel trims learned while the problem was there.

Take a log and we will look at it.
I reflashed Friday night after fixing the leak. This log was taken Saturday afternoon with about 40 miles or so after reflash, I’m guessing before LTFTs were completely learned. Cells are color formatted for load>1.25, KR>2, STFT>10. I will upload tune shortly as it is different than before.


https://www.dropbox.com/s/hsrd5edclgia9 ... .xlsx?dl=0
2007 Mazda CX-7 AWD Grand Touring - Electric Blue Mica
CST4 turbo, CS 3.5bar MAP, CS Stage II SRI w/ TIP, dual port BOV/BPV, 3 port EBCS, 3" TBE w/ Magnaflow muffler, KYB Excel-G shocks, deleted catalytic converters
Disabled EGR, 2nd O2, VTCS
mituc
VersaTuner guru
Posts: 1324
Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: Calibrating MAF

Post by mituc »

Well it doesn't look bad at all.
For the sake of efficiency and predictability you should go to 100% recirc though.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
zaclaw
Posts: 42
Joined: June 9th, 2017, 9:29 pm
Location: South Carolina, United States

Re: Calibrating MAF

Post by zaclaw »

2007 Mazda CX-7 AWD Grand Touring - Electric Blue Mica
CST4 turbo, CS 3.5bar MAP, CS Stage II SRI w/ TIP, dual port BOV/BPV, 3 port EBCS, 3" TBE w/ Magnaflow muffler, KYB Excel-G shocks, deleted catalytic converters
Disabled EGR, 2nd O2, VTCS
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