MAF and predetermined values

[DeeTurbo]

Hi,

I was wondering when the MAF gets old and contaminated I'm guessing the MAF values are high and the ECU over fuels?

But when you disconnect the MAF are the predetermined values set higher, lower or about right?

What sort of values on PP2000 show that a MAF is good or past its best?

Sorry for all the questions but it's been on my mind. I hope someone can answer them and other people find the answer helpful to.

[lolsteve]

Thought generally MAF tend to under rear resulting in the lower power. Unplugging defaults to 550mg/s (I think) which is like midway?

[DeeTurbo]

The reason I thought over fueling is that I've seen cars get smoky on a faulty MAF.

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[Ruan]

When the airmass sensor registers a fault (fboSLMM=1), there is a default airmass map inside the ECU which determines the value used as the current airmass per cylinder stroke (for anyone reading along at home - armM_List) and thus used in the smoke limiter axis. IME it depends on the software version as to the values in this map - 206 is different to 306 and iirc I've seen differing values between 306 variants. The maps axes for the default airmass maps (in the case of the HDi90...) are Engine Speed in RPM (Y Axis - along the top) and Atmospheric Pressure in millibar (X Axis - up the side) and outputting the mass of air in each cylinder stroke (mg/str).



So in answer to your question - as standard, the "default" airmass values used will allow full fuel up to the maximum torque limiter value, hence why unplugging it will cause the management to provide full fuel, even if there are boost leaks or even if the turbo isn't spooled, it has no idea. The MAF sensor can fail in so many ways, positive or negative - usually negative however. There are many, many things that can set an airmass sensor fault - if you want to see what values are being derived, unplug your MAF and watch on PP2k - it will show you the default airmass value being used at present, however from PP2k it's often difficult to notice when the default airmass map is in use or it's actually using the airmass sensor - only thing that will tell you is whether there's a fault code set for the MAF sensor.

Essay over.

[bashbarnard]

As there is a thread up about this. Due to the failing process is it possible to get a dip in mpgs first as lus is going down


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[DeeTurbo]

Ruan, thank you for taking the time to write that, it helps a lot.

I was on the understanding that most MAF's miss read from contamination, build up of "stuff" on the hotwire element.

What would make the MAF under read?

[JTaylor2005]

The MAF sensor would under-read with contamination. The dirt on the hot wire means it doesn't cool correctly as it's covered in dirt. This makes it think less air is flowing through than there really is.

This thread posted by Pro-Steve (HDI Tuning) is a good read here
https://www.theywhoshallnotbenamed/forum...st-the-MAF

Snippet of checking the air flow rates on a good maf.

"What values should you see in PP2000:

Without a remap you should see approximately 850-900mg/r at full load in third gear around 3000 RPM. With a stage one, air flow will be a bit higher due to the extra turbine drive, you'll see over 900 mg/r, nearer 950 mg/r max. With a stage 2 you should see something like 1200 mg/r max depending on how much you've wound the boost up. If you see massive figures like 1400 mg/r you've likely got a boost leak, this results from the turbo having no restriction so it can suck loads of air through the MAF.

Whilst I'm at it, I may as well let you know what to expect on idle with no load. With EGR: 250-300 mg/r. With EGR unplugged 450-500 mg/r. If you have lower than 250 then it's possible your EGR is jammed open.

As a lot of people use other diagnostics systems which give readings in g/second or kg/hour here's some simple calculations:

To convert from grams per second to mg/ rotation: ((MAF reading in g/s) x 60000 ) / (2 x (Engine speed in RPM)) = air mass in milligrams per intake per cylinder

To convert from kilograms per hour to mg/ rotation: ((MAF reading in kg/hr) x 1000000 ) / (60 x2 x (Engine speed in RPM)) = air mass in milligrams per intake per cylinder."

[DeeTurbo]

Thanks, that's some great information.

[Ruan]

Just as a side note to save any confusion, remember it's not mg/rev - rather mg/stroke.

mg/rev does work on a 4cylinder engine (4stroke, 4 cylinder per revolution of the crank there would be one induction stroke) - however this doesn't calculate out for a 5 or 6 cylinder. The ECU knows how many cylinders the engine has, the current mass flow rate and the engine speed - therefore it can derive how much air is being delivered per stroke.

[dr_jekyll]

When the airmass sensor registers a fault (fboSLMM=1), there is a default airmass map inside the ECU which determines the value used as the current airmass per cylinder stroke (for anyone reading along at home - armM_List) and thus used in the smoke limiter axis. IME it depends on the software version as to the values in this map - 206 is different to 306 and iirc I've seen differing values between 306 variants. The maps axes for the default airmass maps (in the case of the HDi90...) are Engine Speed in RPM (Y Axis - along the top) and Atmospheric Pressure in millibar (X Axis - up the side) and outputting the mass of air in each cylinder stroke (mg/str).



So in answer to your question - as standard, the "default" airmass values used will allow full fuel up to the maximum torque limiter value, hence why unplugging it will cause the management to provide full fuel, even if there are boost leaks or even if the turbo isn't spooled, it has no idea. The MAF sensor can fail in so many ways, positive or negative - usually negative however. There are many, many things that can set an airmass sensor fault - if you want to see what values are being derived, unplug your MAF and watch on PP2k - it will show you the default airmass value being used at present, however from PP2k it's often difficult to notice when the default airmass map is in use or it's actually using the airmass sensor - only thing that will tell you is whether there's a fault code set for the MAF sensor.

Essay over.

Sorry just read this thread (mildly late)

With a healthy maf will the ecu potential fuel higher then with the maf unplugged or just give a much more efficent atomisation?
Just wondering as notice a huge difference with mine unplugged but alway wondered if a new maf sensor would exceed the feel of the car over when i unplug the maf?

If that makes sense. Cheers

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[Ruan]

It totally depends how the calibration has been done in the remap.

I can only tell you what would happen on a stock file as it depends on software version and how mrwBRA_KF (MAF Limitation or "Smoke Map") has been calibrated. There's so many different ways of calibrating the MAF limitation map that it's difficult to say definitively yes or no - also no reason to say that arwLMVGWKF (default airmass map above) hasn't been re-calibrated to account for a larger turbocharger and higher MAF values when the MAF sensor is in fault.

In this particular scenario - if your software version uses the values that I've shown above - theoretically with a new MAF sensor, the value used in mrwBRA_KF would be higher - whether that allows more fuel is difficult to say because that depends how the limitation map is calibrated. This won't give any "more efficient atomisation" which will improve power remotely noticeably - this is all down to limitation of the injection quantity (and therefore smoke...) depending on how much air is passing through the MAF sensor. With the MAF unplugged, there's corrections made by the ECU which will improve economy (MAF sensor also has a inlet temperature sensor...) which is also used to make small corrections to timing and quantity here and there which certainly help economy/emissions.

There shouldn't be a situation where your car goes better with the MAF sensor unplugged - if it does, that's 99% likely because the MAF sensor is broken and you need a new one.

[dr_jekyll]

It totally depends how the calibration has been done in the remap.

I can only tell you what would happen on a stock file as it depends on software version and how mrwBRA_KF (MAF Limitation or "Smoke Map") has been calibrated. There's so many different ways of calibrating the MAF limitation map that it's difficult to say definitively yes or no - also no reason to say that arwLMVGWKF (default airmass map above) hasn't been re-calibrated to account for a larger turbocharger and higher MAF values when the MAF sensor is in fault.

In this particular scenario - if your software version uses the values that I've shown above - theoretically with a new MAF sensor, the value used in mrwBRA_KF would be higher - whether that allows more fuel is difficult to say because that depends how the limitation map is calibrated. This won't give any "more efficient atomisation" which will improve power remotely noticeably - this is all down to limitation of the injection quantity (and therefore smoke...) depending on how much air is passing through the MAF sensor. With the MAF unplugged, there's corrections made by the ECU which will improve economy (MAF sensor also has a inlet temperature sensor...) which is also used to make small corrections to timing and quantity here and there which certainly help economy/emissions.

There shouldn't be a situation where your car goes better with the MAF sensor unplugged - if it does, that's 99% likely because the MAF sensor is broken and you need a new one.

Cheers for that and taking the time to explaine that fella. Managed to get my head around that. Deffo sounds like im needing a new maf going by that information then as she goes like a rocket unplugged

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