MAF Question | AEM
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azfiveoh
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MAF Question

Is anybody with a series 2 using a MAF?  If so, how well does the functionality work?  Thanks for any input.

Kurt
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I'm using it on my 97 Supra

I'm using it on my 97 Supra with a hotwire MAF.  It works really well.  The difficult thing will be getting proper values to use for your particular MAF sensor, though.  There are a couple of calibrations set up for MAF in the AEMTuner download for you to look at.  MAF Max/Min volts options and the MAF sensor cal table are the ones you'll need to have.  Load Max and Load Offset/Scalar simply convert the MAF g/rev reading into a "kPa" value.  Your fuel table will be in g/rev and the ign table will be in kPa.  In reality, both are in g/rev.  The calculation AEM uses to get to kPa load rows in the Ign table is ((MAF as Load/Load Max)*Load Scalar)+Load Offset.

If you can get the proper settings for your MAF, then it just takes a little math the set up your fuel table.  You'll set your load breakpoints based on how much air mass you expect the engine to take in.  In my case, 3L naturally aspirated 6cyl, it might see something around 1.9g/rev at peak VE WOT on a very cold day.  Maybe 0.5g/rev at idle.  So set the breakpoints according to the airflow your motor will see.  

To set the values in your fuel table, you'll need to determine g/ms of fuel you get from your injectors.  For example, 1,000cc injectors would flow about 0.0125917g/ms of E10, assuming 0.75g/cc density.  Once you know this, the calculation for the numbers to put in your fuel map is going to be:   ( ( (airmass / (#cyl / 2) / (fuel stoich a/f) ) / (fuel flow g/ms)) / target lambda

So, for example: 3L 6cyl, E10, 1,000cc injectors, load row 1.60, desired lambda 0.85..    1.6/(6/2) = 0.5333      0.5333/14.13= 0.037745      0.037745/0.0125917= 2.9976   2.9976/0.85= 3.5266    So, for all rpm points on the 1.6g/rev load row you'd put 3.53.  Set this up in a spreadsheet and you can change the g/rev load row value and desired lambda and populate your fuel map very quickly.

I set up my fuel map with just doing this math and the car started and idled/drove great with AFR very close to what I wanted.  This was due to the MAF cal table being in the ballpark, though!  Once you've set your fuel map based on your desired lambda target, you simply tune the MAF cal table until you're getting that desired target.

azfiveoh
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This is fantastic information

This is fantastic information, thank you!

I've got a series 2 wired up into a 92 mustang and am also using a hot wire MAF.  The car makes almost 1100rwhp and I've got a MAF scaled to just slightly above that number.  The challege I had with the series 1 was setting up the MAF cal table at the lower end of the scale.  There wasn't enough resoltion in the scaling and the numbers ran on top of one another. The manufacturer of the MAF provideds a 30 point transfer funcation and I also had them bench cal the meter at the breakpoints in the AEM cal table.  Because of the lack of resolution I could never get the car working with the MAF on the series 1.

Any thoughts on how I might address the issue with the cal table and how to best estimate the g/rev for max power and at idle?

Again, thanks for the extremely helpful and educational reply!

Kurt
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Yeah, that's the unfortante

Yeah, that's the unfortante thing with a 8bit table.  Can you post your maf calibration?  What range of the maf voltage are you seeing at idle and part throttle cruise?  For reference, the lowest voltage values I'm seeing with my maf are on engine braking in gear down to 1500rpm or so.  It'll be around 1.45-1.5v.  At idle, it's around 1.6v.  2000rpm at 15% throttle cruise it's around 2.5v.  It's about 2.7v at 3000rpm.  Light load voltage range for me is 1.5-2.7v.  Your range will almost certainly be less.  Once you know all this you may be able to work around the resolution issue.  If you can simply have increasing g/sec settings in that voltage range then you should be able to tune the fuel map cell by cell and get acceptable results.  So, in my case, I'd set the 1.4v breakpoint to zero, 1.6v would be 1 to 2 steps up, 1.7 1-2 more, etc.  Just do this for the problem area up to the point where the correct maf cal info is correct.  The problem is having the same g/sec value between breakpoints which will give you the same g/rev output at each rpm point even if there is actually more or less airflow.  The final g/rev resolution that you will get from the MAF as Load channel is 0.02g/rev.  Having increasing values along each voltage breakpoint will give you something useful to work with.  You'll just have to adjust your fuel map breakpoints for the small range in that area.

Having said all that, I'd suggest you just go with speed density fueling for forced induction application!! lol

azfiveoh
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Joined: 01/07/2015 - 07:39
I'd be happy to post my

I'd be happy to post my calibration file, I just don't how to attach the file.  The table below shows voltage and correspond flow in kg/hr

FlowVolts
4.5110
9.183.16
15.897.31
26.152.47
39.244.62
57.569.78
81.084.94
108.4831.09
144.1211.15
184.1991.4
234.7881.56
294.2351.72
358.7181.87
437.5982.03
521.7282.18
623.1102.34
737.3332.5
856.8342.65
998.3612.81
1144.982.96
1317.0713.12
1506.2343.28
1699.8733.43
1924.6643.59
2153.33.74
2417.1363.9
2702.4814.06
2990.3544.21
3320.0324.37
3651.1274.52
4028.6924.68
4432.3794.84
4835.424.99

I've never been able to get the car to start on the MAF.  I played with a few parameter and the car would just crank like it wasn't getting any fuel or spark.  I eventually gave up, went back to speed density.

When I scale the range for the top end the bottom end does not have the resolution and two or three voltage points end up being the same number.  Something I haven't tried is using the stock 5.0 mustang cal table.  This meter is designed to work with a factory computer in an 89-93 mustang and therefore I'm wondering if by rescaling the MAF table I may be introducing a problem.

My gripe with speed density is that the car drives like a speed density car.  There are some aftermarket companies, like SCT and PMAS, that make large flow air flow meters and the cars they are turning out drive really well at light loads and transitions while still making gobs of power.

It is a forced induction application.  I'd like to experiment with the air meter and see how the car responds.  I've got a pretty good tune in it now for speed density but you can tell you're driving a speed density car.

Thanks, again, for your help!

Kurt
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Good feedback!  That's

Good feedback!  That's something I immediately noticed as well with drivability.  Speed density works fine but switching to maf made it behave a lot better.  AFR is always instantly right at target and rock steady.

Cranking fuel comes from initial pulse and cranking fuel tables.  Maf reading is only used above crank exit rpm. 

Kurt
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Here's something you can try.

Here's something you can try.  Converting your table from kg/hr to g/s gives something close to the table below.  With a 498g/s range, you won't be able to enter the entire calibration.  473g/s at 3.4v is the highest that you'll read within the correct scaled range of your MAF sensor.  If we assume 1.8hp per cfm of air, then the 473g/s range of the MAF table would give something up to around 1400hp.  So, assuming you're within that range, you should be operating in a 0-3.4v rane of the sensor and the points above 3.4v won't ever be reached so it won't matter that the MAF table can't account for the full range of your sensor.  If you are exceeding that range, then you can start to play with the numbers a little and scale it all down some.  This would give a % lower g/rev value but would be easily accounted for and you could include more of the MAF calibration into the table.  I'm guessing with a 5L engine, you'd see 0.6g/rev to 2g/rev normally from idle to part throttle driving around.  You could spread that over half or more of the lower load breakpoints.  For the higher load range, each load row really just functions as an AFR target, so you don't really need a whole lot of them if it's the same target for a large load range.  For the lower load range where the coarse resolution is the problem, you'd want some more points so you can tune cell to cell in the fuel map.  

azfiveoh
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Joined: 01/07/2015 - 07:39
Great information, thanks!

Great information, thanks!

On the dyno the car is maxed out at 1085rwhp so the range you've shown will work quite well as it will ensure the meter does not max out while not being too far out of the scope of reason in terms of max flow through the meter.  My current load breakpoint setup for the SD map is exactly as you've described for the MAF breakpoints.  I have a 5.8L engine and the resolution at the lower load rows is fine due to that being the drivability area.  Anything venturing into the positive MAP area essentially acts as an AFR target so the spacing is pretty coarse.  It works quite well for optimizing the load cell.

I'll finish up the spreadsheet and start messing around with some values in a test cal to see if I can get the car to fire and idle normally.

Thanks for all the help, I'm excited to have another go at trying to get the car running on the MAF!