Thread: First run of new evo-logged Air flow circuit HIGH

Originally Posted by mturri

Have a few more on the shelf that haven't had the time to test, on the project list though.

Would be interesting to see what PhillipA's seemingly hypertrofic MAF resistivity readings are...

Cheers
Matt

Hi Matt,

We've seen a few brand new VDO Siemens that read 21 Mohm out of the box and work perfectly.

My MAF is reading 15.4M Ohm on pins 1-3 and 2-3 but will still register 645 kg/h at full load.

I'm inclined to think that your classification "dodgy" is perhaps kicking in too early and down to 15M Ohm at least the MAF should still be perfectly functional. Describing a 19.34 MOhm reading as dodgy seems a little odd when a new VDO unit reads 21MOhm. This figure was seen by myself , and by another member who checked on 3 meters including a calibrated meter at his workplace.

I'd also be interested in seeing resistance readings from Philips superMAF. Maybe we can organise something?

cheers
Paul

Originally Posted by OffTrack

I'm inclined to think that your classification "dodgy" is perhaps kicking in too early and down to 15M Ohm at least the MAF should still be perfectly functional. Describing a 19.34 MOhm reading as dodgy seems a little odd when a new VDO unit reads 21MOhm. This figure was seen by myself , and by another member who checked on 3 meters including a calibrated meter at his workplace.

Point taken. Have removed the subjective bits. The point being illustrated is the apparent correlation between the decrease in 1-3 & 2-3 resistivity values and 'MAF wear'.

Cheers
Matt

Originally Posted by mturri

Point taken. Have removed the subjective bits. The point being illustrated is the apparent correlation between the decrease in 1-3 & 2-3 resistivity values and 'MAF wear'.

Cheers
Matt

Hi Matt,

The MAF wear is interesting, and would be good to get a better idea of the acceptable limits.

It's pretty astounding the difference cleaning makes:

MAF before cleaning:

1-2 16.75 kΩ
1-3 2.405MΩ
2-3 14.35MΩ

MAF after cleaning

1-2 16.73kΩ
1-3 15.41MΩ
2-3 15.50MΩ

2-3 seems far less sensitive to contamination of the elements than the other two, and 1-2 is apparently unaffected.
The discrepancy between 1-3 and 2-3 seems a good way of identifying a dirty MAF.

cheers
Paul

before I go further , which do you consider 1?
Towards Front of car or rear.
Regards Philip A

Originally Posted by PhilipA

before I go further , which do you consider 1?
Towards Front of car or rear.

Should be rear...

I worked it out by multi meter and looking for 16.7Kohm, logically pin 2 is centre so it was a 50/50 chance: from there p

My new VDO MAF tested in the mid 20 Mohms across pins 1-3 and 2-3.

Cheers

Steve

Just noticed the symbols between the numbers.

au is Silver element
sn is Tin element

I'm wondering how much influence ambient temps have on the resistance readings? The resistance should increase as the temperature rises, so you'd expect to see some variance in resistance with a 20-30°C ambient temp change.

cheers
Paul

Thought I might post a link up a very basic tutorial on how a Hot film MAF works (altough this converts the analogue signal to digital.
http://training.avme.net/admin/Upload/SSP/4864_358%20Hot%20film%20Air%20mass%20meter%20HFM%2 06.pdf

Resistance testing has so limited use. It will never show a good MAF sensor and will not find alot of bad ones and unlikly a contaminated one. Just to many variables. It's like testing your hot water thermostat with a multimeter at the power board outside your house. Too much inbetween.
Ambient temp is one variable. Another is your multimeter, the way it measures resistance, the direction of current flow working on the internal cicuitry.
Contamination causes problems as it basically wraps the thermistor and element in a blanket therefore reducing the cooling effect of airflow. The microcontroller sees this as reduced air flow and reacts accordingly. This is why a resistance test is unlikly to show a contaminated sensor.

Live data is will give some info on what the state of your MAF sensor is. A scope also helps - on a diesel there is less feed back but it's still good for a reaction test.

Looking at the live data. The one thing that looks strange to me, not nessisarily the problem, but something I would keep in the back of my mind. Is this vehicle appears to gain altitude faster than a fighter jet around the point the fault occurs. The baro figures are all over the place.
As I said, just something I would keep in the back of my mind.

HTH