Td5 D2 engine - MAF Sensor (2)

With a new MAF on its way, I decided to delve more into the construction and workings of the MAF sensor using the removed example.

I started to think about removing the actual sensor from the MAF body. This will no doubt end in the destruction of the unit but I am so curious as to how it is assembled. Just as curious to discover the meaning of the mirrored surface on the sensor base.

Read that in operation, one of the wires can get heated to +200°C above the ambient temp, so there is probably some strong insulation going on here... The sensor wires are supplied with 12v so in theory I guess (without seeing inside) the wire itself gets 12v and therefore is going to have to be pretty thin to achieve the resistance value to get to 200°C. Add together all the duty cycles running hot and cold, the thermal expansion pressure and the engine/suspension vibration... Tough time in a harsh environment.  Respect the MAF  !!

Attention turned to the two wire elements. The resistance readings I obtained would suggest that their circuit was broken. I probed the mountings of each wire for continuity and there was none. Perhaps these wires were already snapped.?

The wires are very fragile and their delicate mounting seem flimsy. I guess this is to do with their resistance properties. I'm beginning to see why they are so expensive. The manufacturing tolerances must be high and that in turn raises the quality control, the expected lifespan and the end cost.

All of the blogs that talk of cleaning the MAF clearly state how delicate the two sensor wires are and to avoid any contact with them. In theory, any 'dirt' particles can only come downstream from the air filter carried on the air stream and to settle on the tiny heated wires is a big ask. I guess the big concern would be residues burnt onto the surface of the wires altering the thermal cooling of the wires and thereby leading to 'altered ' readings.

I started to think that the wires themselves through their heating action are probably self cleaning and should be left alone if there is no visible debris on them.

The cleaning method is to use aerosol contact cleaner, carb cleaner or even WD40.  Even the force of the spray can sometimes break the wire. Evaporating cleaners work best. They need to dissolve any dirt then wash it away and evaporate. I decided to use Meths and some electrical switch cleaner. .

Initially I thought of making a 'bath' of meths that I could sink the whole sensor into (at least up to the wires), but on reflection abandoned that idea. The only visible dirt I could see was on the end guards and caught on the fine wire mesh behind the 'leading' guard. Photos were taken before the cleaning began..

I resorted to pricking out the dirt from the wire mesh using a thin wire poked through to dislodge it. The internal surfaces of the sensor were wiped down with a cotton bud soaked in meths. There was not much dirt in there at all. I wiped the sensor mount carefully and avoided the actual wires. There was a little yellow spot on the sensor mount body that dissolved away with the meths.. I assumed it to be some kind of manufactured colour code?

At this point I had a clean but none functioning sensor. Attention now turned to the wires themselves.

It was impossible to see any breaks in the wires so I decided to physically touch them with a probe and sure enough the first wire tested flexed away from one of its mounts confirming a break and the lack of continuity and the infinite resistance. The second wire, well see below...

This wire just disintegrated before I could visually see any separation from the terminals. Luckily I had placed a piece of plain white paper inside the sensor to act as a non-distracting background. The paper caught the wire fragments and revealed the golden colour of the 'wire'.  This made me wonder if the wires are actually gold, considering the electrical non-tarnishing qualities of the metal. ?

Alas, not gold! I mean if studied real close it is possible to see that the 'gold' colouring is indeed some kind of non-conducting coating on the surface of an exceptionally fine wire. 

Research on Rave and on the net speak of a 'film coated wire' at the heart of the sensor. 

I then set out to get continuity between the wire mounts by using bare wire and test leads...

I was quickly able to confirm continuity between all the sensor-wire 'poles', but I could not get any continuity to any of the 3 pins on the connector. I was getting ready to break-in to the sensor body when the postman brought me this. ...

.. the new MAF sensor.