Air Mass Meter
2008-08-26

     It is necessary to maintain an exact air/fuel ratio in order to comply with the required vehicle emission limits prescribed by the law. To achieve this, you need to ensure that you have properly working fuel injection system components that would provide your car with an accurate airflow and fuel flow. Among the indispensable parts that comprise your entire fuel injection system is the air mass meter. This car component can be usually seen adjacent to the air filter assembly inside your engine compartment. Also known as an air flow meter, the air mass meter serves a basic role of regulating the airflow that is being delivered to the air intake system in your internal combustion engine. 

     In an Air Mass Meter with a Torquer drive, the rotor of the drive motor is seated directly on the shaft of the throttle butterfly. In order to achieve permanent axial retention of the shaft in combination with simplicity of an assembly, the rotor is press-fitted on to the shaft, then a retaining washer is provided between the throttle butterfly and the rotor. The retaining washer is fixed axially on the shaft or on a throttle housing and engaging with a defined axial play in a gap on the other element. The two axial, housing-side contact surfaces of the retaining washer being formed by a fastening plate screwed to the housing and by a stop provided on the housing. The narrow axial retention device allows rotor-side arrangement for simpler assembly in combination with a short and rigid throttle-butterfly shaft.  

    As an air consumption mass measurement system, the air mass meter works through the principle of hot meter anemometer principle. It does this by sending an electronic signal to the onboard computer of your car as a response to the amount of fluid flow in your engine. Gasoline engine cars can either be equipped with a hot wire or a vane meter type of air mass meter. A hot wire determines the air mass into the engine by heating an electrical wire that has been suspended in the air stream. On the other hand, a vane meter sensor features a spring loaded arm that is used to measure the air volume in the intake air stream of your engine. Just make sure that you keep contaminants on the electrodes inside this fuel injection component. A contaminated air mass meter would result to poor idle or hesitation in acceleration. When your stock air mass meter needs replacement, it would be wise to consider some specifications like fluid temperature range, operating pressure, accuracy and mass flow rate range. 

     Well, if you imagine that everytime your car is driven the vane or electrical wire inside is having air passed over it. Although this air has been filtered via the panel filter within the airbox, there will still be minute particles of dust and pollen etc. that will build up over time and reduce the air mass meters efficiency. Eventually it will stop working and this usually results in a significant affect on your cars power and its fuel economy.

     It is not a part that will last forever, and although there are people that state that you can clean the internal parts, it is probably better in the long run if you just get it changed when it finally does stop working. Here are some tips for you: 

What can go wrong with the air mass meter ?        There was an intermittent fault on my VW Sharan (turbo diesel) whereby on occasion after a long run or having a lot of people in it, the power would disappear and the turbo was virtually non-responsive. After a while or if I switched the ignition off, the problem would go away but it kept doing this for about 6 months. I had a search around on the internet and looked in many online forums and found that the most likely cause was the air mass meter was on its way out. I had the option of giving a clean to see if this would get rid of the problem, but because of the miles this car has done I decided that this would be a waste of time and would get round to replacing it at some point or to get it changed when it finally gave up for good (whichever situation would come first).        With my VW Sharan when the air mass meter did not give any signal out to the ECU, the car would switch itself into 'limp mode'. This 'limp mode' was the cause of the lose of power and it was the ECU (cars computer) running in a mode that would minimise any damage to the engine

How to change your air mass meter?       On the VW Sharan, the air mass meter is situated on the left of the engine bay behind the airbox. It is bolted onto the airbox at one end with 2 x 8mm allen bolts and clamped at the other end onto a plastic air pipe with a clamping ring.     

1. Unplug the wiring from the meter by squeezing the clips wings inwards and pulling up. Do not pull it by the wires.

2. We will start off by removing the plastic pipe at the back of the air mass meter. When you push the the 2 clamping ring wings towards each other, the diameter of the clamp increases allowing you to push the pipe off the end of the meter. With your right hand take your pliers and put them over clamping ring wings, push the pliers together and as the ring opens, separate the pipe from the meter with your left hand. You can leave the clamping ring in place around the loosened pipe.        

3. The next thing to do is to unclip the top off the airbox and turn it over. This will be easy now you have removed that plastic pipe, and noe of the other pipes on the airbox will need to be removed. Turning over the airbox lid at this point will make it easier to remove the 2 x 8mm allen bolts holding the meter. There are 2 clips holding the airbox lid in place, one at the front and one at the back. Locate one of the clips, put your hand down there and feel the bottom of the clip. If you pull the bottom of the clip upwards, it will release the top of the clip. Push the top of the released clip away from the airbox lid and repeat with the other clip.      

4. Now you should have easier access to both of the bolts holding the air mass meter. Undo the 2 x 8mm allen bolts using your 8mm allen key. Once removed make sure you put them in a safe place. The meter should now separate from the airbox, make sure that you retrieve the large 'o' ring from the outside of that end and fit it to the new air mass meter.           

5. Fitting the new air mass meter is a direct reversal of what you have just done ; a. fit the old 'o' ring onto the new air mass meter b. bolt the meter back onto the lid of the airbox c. clip the airbox lid back on to the airbox, making sure that the panel filter is seated correctly d. Connect the plastic pipe back onto the other end of the air mass meter, making sure that the clamping ring is securely in place e. reconnect the wiring plug onto the top of the meter