MAF cleaning

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warpc0il
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MAF cleaning

Post by warpc0il » Tue Feb 15, 2011 5:51 pm

What is the MAF?

The Mass Air Flow sensor is a device for measuring the amount of air flowing into the engine. A larger quantity of air entering the engine indicates acceleration or a high load situation, while a smaller quantity of air indicates deceleration or idle. The engine management unit receives the signals from the MAF sensor and judges the engine operating position and varies the amount of fuel injected to match the requirements.

The RX-8 MAF unit also includes an Intake Air Temperature (IAT) Sensor, this detects the temperature of intake air drawn into the engine. Air density changes depending on the intake air temperature, which changes the oxygen concentration of the intake air. Therefore, the intake air temperature sensor prevents unstable combustion due to deviation occurring in the air-fuel ratio.

Club Members can learn more about the Mazda Engine Management System by accessing the CBT here.

Why would I need to clean it?

Contamination of any sort will have a degrading effect on the function of the MAF and result in incorrect fuel mixture. The resulting symptoms can be any combination of:

- poor starting
- rough idle or stalling
- increased fuel consumption
- poor acceleration
- hunting on steady throttle
- hesitation on pull-away
- black smoke from exhaust.

How does it get dirty?

There are 4 main ways that the MAF can get contaminated.

1 - There will always be some small particles that make it through the air cleaner element and get drawn past the MAF; e.g. the particulates in diesel smoke. These can build-up over time and form a residue on the sensor wires. Cleaning or even checking the MAF is not part of the standard Service Schedule, though many believe it should be, and a quick clean every 10-20k miles (depending on your driving conditions) can make a big difference, especially if there is any experience of the issues listed above.
This applies to all RX-8s.

2 - Some aftermarket air filter elements attempt to trap smaller particles by having a slightly sticky surface. While this can be effective it can also have a downside. The stickiness is usually an oil-based compound that is pre-applied to new filters and can be re-applied, usually by aerosol, on the washable versions. Sometimes the factory application can be uneven and it is particularly difficult to manually apply evenly and to the correct coverage. Any excess compound will be drawn off the filter, into the intake air and can contaminate the MAF. This only applies to RX-8s with sticky filters and you should clean the MAF after 50-100 miles of fitting a new filter or servicing a used one. This does not apply to the OEM filter or normal "paper" aftermarket replacements.

3 - Overfilling the engine oil level will result in oil spray or even liquid oil being taken into the airbox from the engine breather. Some of this will then get drawn through the filter element, into the intake air and will contaminate the MAF. If you know or suspect the engine oil has been overfilled then open the airbox and inspect the inside surfaces and the air filter element for signs of oil. If there is any oil present you will need to wipe it clean, replace the filter, clean out the intake tube, the resonance chamber and the MAF. This applies to any vehicle that is known to have suffered an overfill or has a sudden onset of the above symptoms, as that may indicate an overfill. The exhaust smoke may be white or blue as the excess oil is burnt in the engine.

An engine that is slightly overfilled with oil might not exhibit a problem until you accelerate hard, which may be days after the last oil top-up. This is down to the sudden increase in intake vacuum under acceleration which pulls more oil vapour from the engine breather.

To avoid this problem, check to oil level as per the manual and aim to keep it one dot below the MAX mark.

4 - If you don't use a long funnel when filling or adding oil it's very easy for oil to run into the upper breather tube, as it connects to the filler pipe. The early cars are prone to this as the breather is attached just under the filler cap. From '06 the breather layout was changed slightly, with the attachment lower down. While this makes it less likely that you would pour directly into the end of the breather, the lower attachment means it's more likely to be an issue if oil is added quicker than it can drain into the sump. Either way, it can give all the symptoms of an overfill, including MAF contamination, while the oil level is (confusingly) below the MAX mark.

Just use a long funnel and take your time, to avoid this scenario.

It's also possible to fit an oil catch tank between the engine breather and the airbox, to capture any oil before it gets to the intake system.

Where is the MAF?

It's located between the airbox and the throttle-body.
MAF location.JPG
MAF location.JPG (83.3 KiB) Viewed 9960 times
Remove the engine cover and you'll see the large pipe running from the back of the airbox with the top of the MAF unit held by two screws.
Disconnect the cable loom, remove the screws and carefully pull out the unit.

What does the MAF look like?
MAF.jpg
MAF.jpg (60.73 KiB) Viewed 9974 times
You can see the bulb of the IAT, which is usually coloured orange/brown.
The MAF sensors are hidden up inside the tube section.

How do I clean it?
The working parts are all delicate and must be treated with care. Replacement MAF units are expensive.
You will need a suitable solvent to dissolve the contamination from the surfaces.
Brake and carburettor cleaners are not suitable and must not be used.
The safest option is a specialist spray such as CRC Industries Air Sensor Cleaner, available through motor factors and on eBay.

Alternatively you can use isopropyl alcohol (IPA) and some products sold as "electrical contact cleaner" may also be suitable but their ingredients vary by brand and many contain a small amount of oil to protect and lubricate the contacts, making them unsuitable for our purpose.

Obviously original WD-40 and the like are a no-no, though the WD-40 brand has now been expanded and includes a contact cleaner.

Whether you choose the dedicated product or an alternative, you need to saturate the working parts of the sensor to soften the dirt and wash it away. This is best achieved with multiple applications with 5-10 minutes in between to allow the chemicals to work. If you have a quantity of IPA then you could soak the unit overnight.

If the dirt is really solid you may try using a cotton bud to wipe the surfaces while wet with solvent. Take care and never be tempted to use anything harder or you will damage the fragile sensor wires. Always finish with a flush of clean solvent and allow to air dry. Don't use a hair dryer or hot air gun as the heat will damage the unit and the vapour is highly volatile and could cause a fire.

When replacing the MAF unit it may help to apply a small wipe of silicon grease or Vaseline to the O-ring to ensure an air-tight seal to avoid air leaks. Don't overtighten the screws or you may damage the threads or distort the mounting face.

Whilst this may all sound very complicated, it's an easy DIY job as long as you take your time and take care.

If it's been running with a dirty MAF you need to reset the ECU, since it will have learnt its fuelling incorrectly.

This should improve performance, economy and stop the stalling.

Follow the instructions here.
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Re: MAF cleaning

Post by SeanP » Wed Sep 10, 2014 2:13 pm

On balance, some very interesting reading from K&N about MAF sensors, and the "myths" of them becoming dirty...

Well, they are defending their "oiled" & cleanble life-time filters being the cause of gunking up MAF sensors... and like the Urban Myths team take their testing to the extreme to see just what it DOES take to make a MAF dirty and mis-read!

One of the many videos from the site:

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Re: MAF cleaning

Post by warpc0il » Sun Feb 25, 2018 9:44 pm

Just a reminder, when removing the MAF, don't drop the o-ring and remember to replace it when refitting.
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