We talked about this before, but I now have a picture to make my question more clear. Any Bosch experts out there??

I removed my '98 E320 MAF sensor - There are apparently three parts to it other than the internal electronics. These are:

- External electronic part mounted on a u-shaped wire - Is this the thermistor for temperature measurement?

- Flow through cavity with shiny plate inside - Is this the hot film? There is also a drain hole on side.

- Dead-ended cavity near bottom - hard to tell, but there appears to be two wires one behind the other - perhaps connected to hot film? What is this for?????

The u shaped wire with thermistor is the air temp sensor. it has little if nothing to do with the fuel calculation. it is mostly used for timing and purge control.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The generic name for mass air flow meters is "hot wire aenemometer". The principal is that a variable current source heats a wire (or grid of wires) to a specified temperature, but the wire(s) is constantly cooled by the air flow. The difference in current required to keep the wire at the predetermined temperature between some non-zero air flow value and zero flow rate is proportional to the mass flow rate, so the wire current is an analog for the mass flow. This analog value is then digitized by the engine control electronics and used to calculate base fuel flow, which is then constantly adjusted by the O2 sensor and associated control system.

The system also needs to detect and correct for inlet air temperature since cool air will cool the wire(s) more than warm air.

Duke

Right ,
I do understand all that.

I can see the thermistor that measures the air temperature.

In this case I presume that the "hot wire" is not a "hot wire", but a hot film - the shiny plate inside the flow-thru passage (They probably went to this hot film design so that water droplets and solids would not impact the hot wire - they just flow on past it.)

My question still is - What is the purpose of the dead-end cavity with 2 vertical wires near the bottom of the sensor - see picture??