Thread: MAF resistance values

thanks Offtrack / SF for your helpful comments ...... I gotta say I'm feeling conflicted and confused now. Now that the MAP is presented as part of the equation (ie has a part to play with the fuelling in a EU2 TD5) maybe I should just replace both the MAF and MAP sensors if only because they're both likely to be original on my D2.

How do I test the MAP sensor...?

onebob

PS: My TD5 is de-EGR'd

The MAP/IAT is 2 in 1. MAP side is made by piezocrystals so resistance measuremets are futile, only the IAT side of it can be measured cos that's NTC, relevant check is with tetser to read live data and compare with a gauge reading...if it's so old better replace it with new without remorse

The MAP reading contains the AAP too which's reading must be extracted from the MAP to get the boost and that's important as well(boost = MAP - AAP, 100kPa = 1 bar/14.5psi )

Originally Posted by onebob

thanks Offtrack / SF for your helpful comments ...... I gotta say I'm feeling conflicted and confused now. Now that the MAP is presented as part of the equation (ie has a part to play with the fuelling in a EU2 TD5) maybe I should just replace both the MAF and MAP sensors if only because they're both likely to be original on my D2.

How do I test the MAP sensor...?

onebob

PS: My TD5 is de-EGR'd

Hi Bob,

Maybe try and track down someone one with a Nanocom/Hawkeye/Lynx/etc and see if you can record as quick road test. A sensor that is mis-reading should be fairly obvious and troubleshooting by replacing sensors one by one is going to get expensive quickly.

You can check the MAP by measuring the output voltage. The only sensible reading is at ambient unless you have some way of subjecting the sensor to a known pressure.

The relationship between pressure and voltage is basically high school math - line slope-intercept formula from the two data points on the MAP datasheet. The output varies by roughly 18mV per 1kPa change in pressure.



Perhaps it's SF english making his meaning unclear but I'd stress that the MAP reading does not contain the AAP value.
MAP is Manifold Absolute Pressure.
The Absolute means that it is referenced to a small vacuum chamber in the body of the sensor which acts as a 0kPa point.
The reading is therefore the pressure above 0kPa.

The MAP and AAP readings can be compared with each other with the engine off and should read approximately the same.
The AAP sensor has a different curve to the MAP so the voltages will not be the same.

FWIW the AAP sensor is located in the lid of the filter/airbox. Because it is located after the air filter it reflects the restriction of the intake and air filter and under heavy load measures well below ambient. AAP readings dropping by 5kPa or more under heavy boost are common.

Paul

Don't take it as a reaction please, just as a friendly discussion, i'm asking something to clarify this

...Perhaps it's SF english making his meaning unclear but I'd stress that the MAP reading does not contain the AAP value.
MAP is Manifold Absolute Pressure
The Absolute means that it is referenced to a small vacuum chamber in the body of the sensor which acts as a 0kPa point.....

what i meant was from the management's point of view not from a physical one

as we know nanocom(i give it as example cos many members have it) shows a "Turbo pressure" value when it's set to instrument mode... where is that value coming from then? or how does the ECU calculates boost? ...as one of the ECU's functions using the AAP reading is "To maintain manifold boost pressure" , or how is the "altitude compensation" achieved?... if RAVE is wrong again in this area i apologise

what i can admit is that maybe i can't explain well everything in english though i insist: for the Td5 engine management boost = MAP - AAP so in my acception there's nothing wrong with my statement

Originally Posted by sierrafery

Don't take it as a reaction please, just as a friendly discussion, i'm asking something to clarify thiswhat i meant was from the management's point of view not from a physical one

as we know nanocom(i give it as example cos many members have it) shows a "Turbo pressure" value when it's set to instrument mode... where is that value coming from then? or how does the ECU calculates boost? ...as one of the ECU's functions using the AAP reading is "To maintain manifold boost pressure" , or how is the "altitude compensation" achieved?... if RAVE is wrong again in this area i apologise

what i can admit is that maybe i can't explain well everything in english though i insist: for the Td5 engine management boost = MAP - AAP so in my acception there's nothing wrong with my statement

SF,

You are misreading what I said, yet again.

I'm probably being a bit pedantic. My point is both MAP and AAP are measurements made against an internal 0kPa reference so the readings are only of the pressure the sensor element is surrounded by compared with 0kPa. The MAP reading is not referenced directly to the ambient pressure or the AAP pressure. The MAP only "contains" the AAP in the sense that the AAP is subtracted from the MAP to find boost as the difference between the two readings.

The Nanocom instrument mode calculates the boost pressure by subtracting MAP and AAP readings from the ECU. The ECU does not provide that information in any diagnostic request. Nanocom also changes Kelvin to degrees Celsius, and makes other transformations to data to make it more user friendly.

The air mass in the cylinder is calculated using the Ideal Gas Law from absolute pressure (MAP) and absolute temperature (IAT).
This is the basis of the fuelling calculations done in the EU2 engine.

For boost limiting and WGM control the difference between MAP-AAP is used.

AAP is also used alone to provide an estimate of altitude for some adjustments to fuelling.

This is precisely what RAVE tells you:

The MAP/IAT sensors are combined in one unit located in the inlet manifold. It provides pressure and temperature information about the air in the inlet manifold to the ECM. The ECM compares the voltage signal to stored values and compensates fuel delivery as necessary. The ECM uses the signal from the MAP/IAT sensor for the following functions:

l To calculate the delivered fuel limits.
l To calculate the air mass in the cylinder.
l To calculate the air speed density.
l To calculate air temperature.

and

The ECM uses the signal from the AAP sensor for the following functions:
l To maintain manifold boost pressure.
l To reduce exhaust smoke emissions while driving at high altitude.
l Control of the EGR system.

cheers
Paul

On altitude compensation using the AAP, pressure obviously drops with altitude.
At sea level standard atmospheric pressure is 101.0kPa.
The highest paved road in Europe has an altitude of 2830metres where the atmospheric pressure would be roughly 73kPa. In Australia the Great Alpine road has the highest point at Mt. Hotham - a tiddler at 1830m, where the AAP should read roughly 81kPa.

If you are planning on doing high passes, the ROW maps are the best option. EU/AU maps have a minimum AAP of 65kPa or roughly 3500m. ROW maps change this to 50kPa, which equates to something like 5200m. That should be ok for Khardung La with maybe a little bit of extra smoke, but the handful of higher passes might be a problem.

Originally Posted by OffTrack

Bob,

You'll notice that the Paddock video shows the idle voltage, not peak voltage.
This is because - as they state - airflow is directly related to engine load.
You can't test the peak MAF reading by reving the engine in neutral because there is no load.

The other thing is that MAF's seem to generally over read rather than under read when they go out of spec. You tend to get higher idle airflow readings and higher peak readings, rather than lower.

The 1.88V reading at idle would mean the airflow is in the low 50's which is isn't too bad. An over reading MAF will idle at something closer to 2.1-2.2V / 70kg/Hr+.

Keep in mind that on EU2's the MAF is not directly used for fuelling. MAP/IAT readings are used to calculate the amount of air in the cylinders.
If you have the EGR still operational the MAF will influence fuelling because the EGR operates to reduce the amount of oxygen in the cylinders and this in turn influences the amount of fuel injected.

The EU3's are significantly different in that they use the MAF as the primary means of calculating fuelling. Unplugging the MAF on an EU3 forces the ECU to use the MAP/IAT and a much simpler fuelling strategy, so it's usually a good indicator of bad MAF performance (on EU3's).

cheers
Paul

My mum always said "'tis better to be late, than never" and so some two months on from your last posted comments I've managed to gather some voltage readings from the MAF with the TD5 under accelleration load and whilst relaxed driving. The highest reading was 4.32V at 3000RPM before the AT selected high gear and then lock up.

I'd welcome comments from the forum guru's regarding whether you think the MAF is dying or is still in reasonable health....

onebob

NB: I unboxed and installed a new RYCO Airbox Filter for this test..

https://youtu.be/EFFJ69g9xuA

Hi onebob, your thread has poked my interest button so iv'e started to look around.I'm definitely not a guru, but it appears to me that resistance only measurement could possibly only highlight shorts or open circuits within the D2's MAF, and to be honest it would appear to be a bit of a futile exercise, as the voltage measurement method VCC the voltage from (F2 I think) to GND and GND to VS (the colloquially know as 0 to 5 V signal the one you have displayed in your video) Interestingly F2 also feeds boost solenoid on the EU3 version.
Anyway I think to hopefully answer your question No The DVM in your video will not show an issue that could definitively say your MAF is on its way out.
First and foremost the what I am now lead to believe as the common failure mode of an analog MAF is what can be described as sluggish response to changes in airflow hysteresis if you will which is caused typically by carbon deposits on the wire, the result in which will be a delay in registering increased airflow which will ultimately will mess up the fueling via the injector pulse widths. Unfortunately the IAT sensor and the MAF sensor are used to work out what to do with the overall driving experience hence driving around will not actually tell you much when it comes to the MAF and IAT for the real picture you need to either have the capability to measure and record both IAT , MAF and RPM relative to time simplest way to do this is with a nanocom (although the nanocom has the logging resolution issue) or other such diagnostics tool and plot the aforementioned signals out. oh and 1.8 ~1.9 V is about the number you'd expect from a D2a's MAF at idle and as far as I can make out it is very unlikely that the MAF would ever get to full scale deflection at wide open throttle on a D2a.

regards