MAF calibration

[Gelf VXR]

Out of interest, what are the average adjustments being needed when calibrating the MAF, for example I am seeing roughly -11% across the Hz range, is this normal?

I'm starting to suspect the injectors that came with the L76 complete intake manifold are smaller the 42lb hr? I use LS3/LS7 injector tables. Its an LS2.

I should check the fuel pressure too

[joecar]

I sometimes see 10-15%.

[Gelf VXR]

Its odd this doesn't get highlighted that much, its quite a drop, is the factory calibrated MAF really that far off, or is it the injector data?

Strange I did find the EROD 2010 LS7 tune file has much lower injector flow base, looks close to stock LS2 injector flow base data actually.

[statesman]

Its odd this doesn't get highlighted that much, its quite a drop, is the factory calibrated MAF really that far off, or is it the injector data?

Most likely the injector data.

[Gelf VXR]

Logic suggests that the MAF and base injector flow rate should be correct from the factory, after all the development they have done, any issue with the fuel trims must be with the hardware or the rest of the tune, imho we should leave both the MAF and injector flow as stock as load, traction control, spark, MPG etc. are dependent on these calibrations. It seems that GM make corrections across different platforms to the B1210 MANVAC/VOLTS calibration, when I tried different B1210 map from the one I was using the trims trended towards zero from quite negative.

I'm logging volts and baro/MANVAC to make changes to B1210 only, although you can not apply BEN or trims directly, I'm trying scaling this map up or down to achieve zero trims on this map. And I'm calibrating VE dynair to stock MAF airflow. See how I get on.

[LastCall]

Has the MaF been moved at all? That can affect the measured airflow.

[Gelf VXR]

Has the MaF been moved at all? That can affect the measured airflow.

No, it's a stock intake and filter


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[5.7ute]

Back in 2009 I came up with a method of calculating offsets assuming the airmass calculation was correct. Never tried it though. I have added it to the bottom of this post to see if my thoughts might help.


From what I have seen so far in the IBPW calculation I believe we can dial in the voltage offset adder with a known good tune on stock injectors. As long as our IFR table is correct for the injector, and we are commanding a decent pulsewidth away from the default pulsewidth & small pulse adjust tables where IFR is linear.
First we make a calc. pid called CALC.IPW
CALC.IPW = ({GM.CYLAIR_DMA}/{GM.AFR}/{GM.INJFLOW})*1000 for a maf set up or
CALC.IPW = ({GM.DYNCYLAIR_DMA}/{GM.AFR}/{GM.INJFLOW})*1000 for speed density.
If GM.INJFLOW is not supported like on our holden platform a custom pid using the lookup() function can be used.
This gives us the part of the pulsewidth that the PCM calculates for fuel minus the offsets & adders. (This pid is also used for other calculations I have been working on so I have kept it seperate from the rest of the equation.)
Then we need to make the pid to calculate the error in the offset. If the offset is too small for the injector, not enough pulsewidth is added & a lean condition will result. The necessary amount to be added is easily calculated by the equation
correction= CALC.IPW -(({GM.CYLAIR_DMA}/{WO2.AFR}/{GM.INJFLOW})*1000) .
This correction can then be added to the {B3701} table.
Note: since we are assuming that cylinder airmass is already correct, this method will not work unless the VE table/ maf curve were tuned previously with a known, accurate set of values.

[statesman]

Logic suggests that the MAF and base injector flow rate should be correct from the factory

Good luck with that. :laugh:


when I tried different B1210 map from the one I was using the trims trended towards zero from quite negative.

Lowering B1210 will lean out the fueling, but so will raising the IFR or lowering the MAF curve... so which of those tables really needs to be adjusted? If your actual fueling in PE doesn't match the commanded fueling for PE, then you've probably adjusted the wrong table.

[Chevy366]

I would think the MAF is a like a calibrated instrument, calibrated to detect a range of air flow derived from a static environment and known air flow rate values.

[Gelf VXR]

Lowering B1210 will lean out the fueling, but so will raising the IFR or lowering the MAF curve... so which of those tables really needs to be adjusted?.

That was the point I was making, adjusting the MAF or base IFR will affect other calculations for load, TC, spark etc


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[Chevy366]

All you are doing is moving a point on the scale, the calibration scale didn't change just the point on the scale within the calibration scale.

[statesman]

That was the point I was making, adjusting the MAF or base IFR will affect other calculations for load, TC, spark etc

No, only adjusting the MAF will alter those calculations. Adjusting the IFR will alter the amount of fuel supplied but will not alter the calculations for load, spark, etc.

[joecar]

I would think the MAF is a like a calibrated instrument, calibrated to detect a range of air flow derived from a static environment and known air flow rate values.The MAF table is like the VE table... the factory may or may have not spent sufficient resources on either, possibly depending on the vehicle.

[joecar]

That was the point I was making, adjusting the MAF or base IFR will affect other calculations for load, TC, spark etc

+1 what statesman said...

IFR and OLFA and PE tables affect fueling only.

MAF and VE affect airmass, load, spark, TC, torque calculations/lookups (and transmission line pressure calculation).


Fueling and airmass/load are dealt with separately.

[Chevy366]

Aren't MAF and VE based on a static air pump volume? Unless you alter that air pump volume in some way the MAF and VE remain the same since the air pump volume hasn't changed. If MAF and VE have such a drastic effect on other parameters maybe we should leave them alone. Then again, maybe all they do is gauge air pump volume.

[joecar]

I would think the MAF is a like a calibrated instrument, calibrated to detect a range of air flow derived from a static environment and known air flow rate values.

Aren't MAF and VE based on a static air pump volume? Unless you alter that air pump volume in some way the MAF and VE remain the same since the air pump volume hasn't changed. If MAF and VE have such a drastic effect on other parameters maybe we should leave them alone. Then again, maybe all they do is gauge air pump volume.What I'm saying is that like any of the other tables, GM does not always calibrate the VE and/or MAF tables correctly and/or completely.

i.e. don't trust MAF table as being gospel correct from the factory... use a wideband to check it, you will be surprised.

[ScarabEpic22]

Remember guys, GM has LTFT and STFTs for a reason, to compensate for variation. MAF and/or VE/VVE may be correct for 10 of their test engines, yet engine production, environment, and so forth all contribute to variation.

You need to calibrate BOTH MAF and VE/VVE when tuning.

[Gelf VXR]

+1 what statesman said...

IFR and OLFA and PE tables affect fueling only.

MAF and VE affect airmass, load, spark, TC, torque calculations/lookups (and transmission line pressure calculation).


Fueling and airmass/load are dealt with separately.

Yes I agree, as in what I said altering either the base IPW or MAF will have knock on affect on MPG calculations in case of IFR or load, spark and torque in case of MAF.

[Gelf VXR]

i.e. don't trust MAF table as being gospel correct from the factory... use a wideband to check it, you will be surprised.

I wouldn't agree that the MAF is incorrect just because the WB indicates the AFR is not the same as commanded, the AFR is wrong for some reason, but we can calibrate the MAF to the inconsistency to achieve the commanded AFR, is this best practice thou?

If we look at the terminology "fuel trims", the ECU trims the fuel not the MAF which leaves all the dependent calculations alone, adjust the MAF and those calcs might now be incorrect, however if as I am trying, tune the injector flow correction modifier table B1210 (and it does vary across platforms where as base IFR does not for the same injector), MAF airmass, load, spark, TC, torque calculations/lookups are unaffected :)

[Gelf VXR]

More than one way to skin a cat.

since I put the MAF back to stock and played with B1210, I'm sure throttle response improved

[statesman]

the AFR is wrong for some reason, but we can calibrate the MAF to the inconsistency to achieve the commanded AFR, is this best practice thou?

It's accepted as best practice... even though it's not.