Dyrexion

iTrader: (11)

ok yeah, then the main problems the lack of tep/pressure sensors.

Ted B

iTrader: (6)

A Ford MAF is a hotwire unit that meters air based upon the reduction of resistance of the hotwire, which is created by airflow, and reports a voltage. It has no pressure sensor, and the IAT sits elsewhere in the airbox. It works fine in any configuration. Ambient pressure is sensed by an external MAP (BAP).

A GM MAF looks (at a glance) like a hotwire unit, but reports in Hz (like a KV), so I'm unclear as to how it really works (I don't own a GM). Are you certain there is a pressure sensor inside that MAF? Either way, given the Ford example, it should not matter.

If the GM unit is indeed a KV item, that tells me that our MAF should work in blow through. However, if the scaling is well off due to the large pressure difference (which makes sense), than it is probably a moot point.

l2r99gst

iTrader: (2)

I think you may be confusing the fact that if a MAF reports in HZ it is a karmen vortex mas.

Only Mitsu uses Karmen Vortex MASes. Ford , as you mentioned in a hotwire MAF. GM is also a hotwire MAF.

A mitsubishi Karmen MAF works very differently than a hotwire type of maf sensor. The Mitsu Karmen MAF is actually counting the number of air vortices that are produced by the airflow as it passes an obstruction. Those vortices are what are measured and counted as a HZ number. The pressure and baro sensors in the mas housing are then used along with the maf scaling tables, etc, to produce a mass airflow.

The hotwire type mafs don't need temp or pressure sensors because they are mass airflow sensors already, which intrinsically has temperature and pressure already calculated. The Karmen mas is a volume airflow sensor, based on a calibration table, so that is why it needs it's own temp and pressure sensor installed in the mas housing.

Ted B

iTrader: (6)

I understand how a KV MAF works, although I was somehow unware of the BAP being inside (I know the IAT is there).

Then you are confirming that a GM unit is in fact a hotwire MAF (which is what it looks like to me). Everything else makes sense. What I do find strange however is that a GM MAF gives a signal reported in Hz, like a KV unit, but is still a hotwire item.

l2r99gst

iTrader: (2)

Here's a good animation that shows what our mitsu mas is actually measuring. It is measuring the karman vortices produced by the obstruction in the airflow:

l2r99gst

iTrader: (2)

Yes, the baro sensor and temp sensor are in the mas housing and yes, the GM is indeed a hotwire maf.

The fact that is reports in hz makes it easier to use directly with maf translators and maybe even directly ported to our ECU. Since the signal already is a mass airflow, though, the temp and baro are usually locked at an arbitraty value where the ECU won't be pulling timing or compensating for anything.

JohnBradley

iTrader: (30)

So this is why they end up so dependent on weather variables for a set tune. The fact that air density alters with temp and humidity, I can tune it on a cold wet day (not very fun) and have it end up a full point leaner by summer. On the MAFT Pro car we used the sensors and inputs from the stock MAF to continue to make correction, where on my car its being left as a set value because I was trying to see the total amount of variance from winter to summer.

l2r99gst

iTrader: (2)

You know, I have seen a few people say this and I am curious as to why. I used to run a blow through GM MAF when the MAF translator first came out years ago. I never seemed to have an issue from summer to winter, but I rarely tracked the car, so maybe I just wasn't looking.

In theory, though, the tune shouldn't change with changing temps due to weather. Since the GM maf is already measuring a mass airflow, it is incorporating whatever the temperature is at that time. Denser air (colder temps) will produce more molecules hitting the wire, and thus a higher reported mass airflow. The locked temp and baro and just because our ECU needs to see values. The Hz is fed into the ECU, already as a mass airflow basically, but the ECU will still use the locked baro and temp values for it's calculation.

But, since the Hz should be higher in colder temps and lower in hotter temps, it shouldn't matter. I'm wondering if there is something else going on in your case from winter to summer. Or maybe some other routines or tables that are being affected. Maybe mrfred can let us know what he has found since he has done a lot of disassembling in the area of the airflow and fueling routines.

Ted B

iTrader: (6)

But that doesn't explain why GM has it configured to report in Hz and not V. Hz indicates oscillation. Ford MAFs are all calibrated using a device known in the industry as a 'tuning fork' (an oscillatory device), so perhaps that is an indicator.



If no real time pressure and temperature values are available, an accurate air mass calculation cannot be made. Both are critical values in calculating air mass. The further the actual environmental conditions deviate from the 'locked' values the further the air mass *estimation* will deviate from the actual.

l2r99gst

iTrader: (2)

No, not true.

The hotwire mafs don't need a temp or pressure sensors in them because they are directly measuring the mass airflow. Our Mitsu mas does not directly measure mass airflow...it only measures volumetric airflow and therefore the mass airflow needs to be calculated and that's why the temp are pressure are needed.

The temp and pressure are not needed in the hotwire mafs because the actual function of the measuring is measuring the air mass directly. Since air mass already includes temp and pressure, they aren't needed. The more molecules (air mass) that hit the wire, the more voltage or current is needed to keep the wire at a specific temp. If the pressure goes up or the temperature goes down, the air mass is going up. But, the air will be denser and more molecules will hit the wire. So, this temp or pressure change is already incorporated into the measurement by the hotwire maf.

In simple terms, we all know the PV=nRT equation. The hotwire MAF is measuring n. It doesn't need to know the P and T because if measuring n directly, the changes to P and/or T are already in n.

Ted B

iTrader: (6)

I'm sorry, but that is wrong. I've reprogrammed Ford EEC-IV systems since around 1994, and those vehicles have an external IAT and BAP which are used only for the mass air calculation. If what you said was correct, they wouldn't need them. But it is incorrect. GM ostensibly includes both sensors inside the MAF, and they serve the same purpose. The hotwire sensor itself provides only one piece of the puzzle.

The hotwire assembly measures voltage potential across a (hot) wire of known resistance that is calibrated in voltage vs. kg/hr at a standard temperature and pressure. If you've seen a mass air calibration chart, you know what I am talking about. The ECU routinely takes samples from the IAT and to a much lesser extent, the BAP. The values from IAT and BAP are applied to correction tables, which serves as a multiplier to the mass air meter's transfer function.

In PV=nRT

n = MAF
P = BAP
T = IAT


If the air is colder, less airflow is needed to see a given voltage. If air pressure is greater, less airflow is needed to see a given voltage.

JohnBradley

iTrader: (30)

So for instance in my application where I have the GM IAT reporting a set value to the ECU to mimic a MAFT application, it is only feeding off the MAP data and calculating in this case from 69.3*F. The stock ECU is totally out of the loop on this one, as the MAFT Pro is converting the MAP voltage to something it can use in terms of Hz which I trim to roughly simulate the same load based on pressure logs I had from prior to the install. The GM IAT is functioning as far as the Pro is concerned but making no correction there either.

I am thinking about this right then?

l2r99gst

iTrader: (2)

I can't comment on the Ford sensors or ECUs at all, since I have never used them or looked into them. My comments are in regards to the GM sensors.

The GM sensors do directly measure the mass airflow. Whether the GM ECUs use corrections or not, I can't tell you that either. But the reason why the GM MAF translator works in our ECU, for example, with a fixed IAT and baro signal is because of the fact that the Hz reading coming from the GM sensor is changing with respect to T and P already. It's already in a mass airflow form. The locked T and P values are simply to keep our Mitsu ECU happy. It still goes through it's calculation for mass airflow, but since the Hz is now changing with respect to T and P, the locked values don't matter, as long as the sensor is calibrated once.

In our Mitsu mas, the Hz isn't changing with temperature. The Mitsu Hz is simply a calibration curve of L/Hz vs Hz. So, the Hz reading from our mas gives a volumetric airflow, which then needs the baro and temp sensor data to calculate the mass airflow.

So, in simpler terms the Hz from the GM sensor is mass corrected already and the Hz reading from the Mtisu mas is not. For the GM maf, it doesn't matter if the temperature or pressure changes...the Hz reading will have that change already incorporated in the Hz value.

Ted B

iTrader: (6)

It is quite simple. If there is no temperature input at all (apparently the case), the accuracy of the tune will deviate as the ambient temp deviates from the ambient temp at the time the car was tuned. This is an apparent shortcoming of this setup.


They absolutely do, which is why GM includes internal pressure and temp sensors. I just did a bit of research on the GMs, and confirmed that GM's oscillating inductance 'cold wire' assembly measures CFM by itself, which equates to a given kg/hr value for one given standard temperature and pressure. Ford's meters accomplish exactly the same thing, as to Mitsus (albeit both via different means). Deviations in either ambient temp or press cause a drift in the accuracy of the reported value, which is why those sensors are present. The ECU constantly makes use of those internal pressure and temp sensors to make the necessary corrections to the mass air value.

If the sensors are disabled or ignored, temperature and pressure are assumed, and therefore there is no means of atmospheric correction.

l2r99gst

iTrader: (2)

It's been years since I have really looked into this, but I believe the temp sensors and pressure sensors are used for a couple of other purposes, like VE measurements and for checking maf operations (to see if it is in error or not). Another thing I remember is that some ECUs that use the hotwire maf heat the wire to 100C above ambient temps.

The temp and baro are not used in the mass air calcuation that I know of. The mass air is being measured directly.


That's not exactly how I understand the function of a hotwire MAF. My understanding is that platinum wire, which is heated via a current, is placed in the airstream, at a set temperature. The resistance of the wire decreases as it's temperature decreases. The mass of air hitting the wire cools it off, and in turn lowers the resistance, which allows more current to pass through the wire to heat it back up to it's set temperature again. That amount of current used to maintain the wire's intial set temperature is directly proportional to the mass airflow. Depending on the ECU or electronics, that current is changed to be output as voltage or frequency.