THE AIR FLOW
METER
Identify, Troubleshoot and Cure Air Flow Meter problems
What is an air flow meter(AFM); how would you recognize it and
what does it do?
The Air Flow Meter (AFM) is an important component in regulating fuel
delivery to the engine.
All modern petrol and diesel engines(about 1993 on) have an Air Flow Meter.
Engines with carburettors do not need an AFM because the carb itself regulates the amount of fuel
and air going into the engine.
How to find the air flow meter on you car
Look for the air intake opening, follow it to the air
filter and usually you will find the AFM either in the filter box or clipped into the pipework going to the
engine
What does the AFM look like?
Photo shows a typical plastic cylinder type of AFM....
......which has been dismantled from its pipework.
Most AFM have an electrical connexion into them. Check this plug is not corroded inside
What does
the AFM actually do?
The AFM tells the Engine Control Unit (ECU) how much air is flowing
into the engine;
this allows the ECU to control the amount of fuel delivered to the injectors.
Please click here to view air flow meter in stock
What are the different types of MAF used in modern cars and how do they
work?
The earlier type of AFM (eg Bosch Jetronic) used a vane or flap inside the meter body; as
air passed by it opened the flap.
A spring then returned the flap towards closed position when the engine speed slowed down.
Later types are called hot wire; air flow (over the wires) is measured by how
much current is required to keep the wires at a predetermined temperature.
Look inside and you can usually see two filaments; these have to be thin to measure accurately the
speed at which air is flowing into the engine.
Which companies make air flow meters? Are there
pattern copies on the market?
Original equipment fitted to European cars is made by companies like Bosch, Siemens and Hella and,
yes there are a lot of pattern copies on the market. Depending on budget you may prefer to fit a
genuine replacement.
How will you know if your MAF has failed? What effects
will failure have on the performance of your car?
The easiest indication is, of course the malfuntion light showing on your dashboard!
Generally the car will start but will run erratically and may even cut out, using more fuel and performing
poorly.
How easy is it to change the air flow meter
yourself?
Fortunately it's an easy job, requiring no special skills or
tools.
© by Andy Hewing B.Sc.
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