MAS Sensor?

[Dieselman]

Originally posted by Steve_Perry
If you think about how the MAS works in the petrol cars (I dunno if the diesels are the same) it's basically a heated wire wafting in the breeze of the air intake just after the air filter, the more air travelling into the engine the cooler the wire gets, resistance changes with temperature so a signal can be fed back to the ECU. S.

It's not quite like this.

The 12V heats the "hot film" to a set temperature which is measured by a thermistor. The amount of current required to keep the film at this temperature is measured via a comparator circuit. The greater the flow of air or the cooler the air the greater the current required to keep the film at the set temperature.

Thus the feedback voltage, (0-5v), increases with airflow, although not necessarily liniarly. Bear in mind also that different engines ingest different amounts of air, so MAFs have to have different characteristics.

Say my engine injests 3000cc of air for every two revolutions whereas a 2 litre injests 2000cc. (Not really true as ther is only about 80% cylinder filling without turbo / super charging the intake air.)

So if the same MAF were used and the output was 4.8v at 5,000 rpm for my car it would only be about 3.16v for a 2000cc engine.
As the same ECUs are used this wouldn't be too good.

 

[Dieselman]

Sym

Can you get the part no.

heres mine for comparison.

MB no.A000 94 12 48

Bosch no. 0281 002 152

Bosch element no. F00C 2G2 003.

another number. 865 293A


beware of prefixes and suffixes they make a difference to the output curve.

 

[sym]

Originally posted by Dieselman
Sym

Can you get the part no.

heres mine for comparison.

MB no.A000 94 12 48

Bosch no. 0281 002 152

Bosch element no. F00C 262 003.


beware osf prefixes and suffixes they make a difference to the output curve.

cheers - will get a definitive answer on this for you from my helpful MB technician contact ! watch this space . . . .

s.

 

[sym]

to add to this . . . looking back seems that yours is definitely different to Graham's . . i.e different Bosch part number . . .

so needs some further investigation !!

s.

 

[Steve_Perry]

Dieselman, thanks for the detailed explanation I love learning new stuff. So they keep the temperature constant and vary the current? Interesting Heh it's still a heated element though

To add to the part number debate I think my MAS is specific to the M112.910 engine (i.e. the 2.4L V6):

Part Number: A 112 094 00 48, Description: Air Mass Sensor, Price £201.10, Qty: 1, Value: £180.99

S.

 

[Dieselman]

Ah Steve that's the assembly part number, whats the number on the actual MAF inside the housing?

 

[sym]

Steve

To be more precise, all I know for definite at the moment is that the V280 part - comprising of housing and removable sensor (the same as VW VR6 engine apparently !) that costs £70 has been compared with the part from a 111.xxx Kompressor engine , and also a 113.xxx V8 engine, and they use the same Bosch sensor part number - what I don't have at the moment is exactly what Bosch part number that is !

No doubt the clever boffins at Bosch and MB will have made the 112 engine part different ... just for fun. . but lets see !

s.

 

[Dieselman]

Originally posted by sym
to add to this . . . looking back seems that yours is definitely different to Graham's . . i.e different Bosch part number . . .


s.

Ah. And also mine doesn't have the zener diode on the other side.

 

[Steve_Perry]

Originally posted by Dieselman
Ah Steve that's the assembly part number, whats the number on the actual MAF inside the housing?

I don't know I didn't get to keep the old duff part. Sorry. I try not to look at the current MAS let alone tinker with it

S.