Mass Air Flow Sensor? (What is it??) - Mercedes-Benz Forum
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#1 (permalink) Old 06-27-2005, 06:44 AM
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Mass Air Flow Sensor? (What is it??)

Hey guys, I'm new to the forum and a new Merc driver.. Sorry for asking such a question, but it seems that everyone has the same problem.

I have a 95' C220 and it has only (30000 KM) on it.. yes, its like a new car.. my parents never drove it..

so what exactly is the Mass Air Flow Sensor?

And btw, does any of the W202 drivers experience "bad" automatic gear changing ? especially from gear 1 to 2. You feel the "bump" in between when they change gear. It seems better gear changing when the mode is on economy.

Thanks,
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#2 (permalink) Old 06-28-2005, 10:42 PM
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RE: Mass Air Flow Sensor? (What is it??)

I've just had mine replaced on my C280. My understanding is that it does what it says on the tin i.e. it calculates the mass of the air entering the cylinders and then tells the computer how much fuel to inject to ensure proper combustion. I think what was happening with mine was that it wasn't measuring the air properly and as a result it was telling the car to inject too much fuel. As a result it was running erratically / too rich which caused it to back fire under hard acceleration.
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#3 (permalink) Old 06-29-2005, 09:13 AM
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RE: Mass Air Flow Sensor? (What is it??)

hey, thanks lots of your information. btw, how'd you know when you know its time to change the MAF? or is there a specific "KM/Miles" you have to run then you know its the time?

mine's still low low 30000KM ( yes its crazy for a 95' car eh? )
but yea..
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#4 (permalink) Old 06-29-2005, 12:26 PM
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RE: Mass Air Flow Sensor? (What is it??)

I don't know about a specific mileage. I noticed that my car wasn't performing particularly well over the past few months and wrote to the forum about it. Someone mentioned that the MAF might be to blame.

Anyway, when I took my car in for a service (non-MB garage) they hooked up their laptop to the engine's computer and it told them that the sensor was right on it's performance limits (i.e. about to wear out). Any MB garage should be able to perform this check - I'm not sure how many non-MB garages have the equipment / know how to do this.

I believe that in certain circumstances, if it is left to get worse it can do crazy things like telling the engine management system to dump a stack of fuel into the the cyclinders!
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#5 (permalink) Old 08-27-2005, 11:17 PM
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RE: Mass Air Flow Sensor? (What is it??)

The hard shifts that you are currently experiencing are most likely caused by a bad mass air flow sensor. i.e. you go to acc. quickly the computer senses the incorrect air flow makes the fuel ratio too rich. then car trys to out drive itself (as if you were taking it to red line when in all actuality you are nowhere near it) then it goes to shift hard to carry the power into second gear hence the hard shift
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#6 (permalink) Old 09-02-2005, 09:48 PM
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RE: Mass Air Flow Sensor? (What is it??)

I have read over and over that this is an easy thing to replace, however I have yet to be able to find out where it is actually located. A few people have said they would email me a picture or something, but they never come through.

I would really like to replace mine as I have 155k miles on a 95 C280 and have the hard shift.

Any guidence, pic, drawing around that might be able to point some of us less handy under the hood?
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#7 (permalink) Old 09-02-2005, 11:35 PM
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RE: Mass Air Flow Sensor? (What is it??)

Welcome to the forum.

FYI, the MAF is always located in the intake stream between the manifold and the air filter. I attached a picture of the one common to the C220. Armed with the pic and knowing where to look you shouldn't have any trouble locating it.

They are pricey little dogs on any vehicle, but look on line for the best pricing if you're going to change it. Personally I've had great luck with www.autohausaz.com and autopartswarehouse.com, both offer free shipping once you hit $50.

You didn't mention miles but hard shifts can suggest a fluid change is in order. It's supposed to be a "lifetime" fill, but most folks seem to change it out, some argue about every 30K, average seems to be around 60-80K. However, the other post is correct, if the MAF sensor is tossing off inaccurate readings, the computer's attempt to compensate can alter shift points, etc.

Good luck and enjoy the ride,
Greg
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#8 (permalink) Old 09-03-2005, 03:21 AM
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RE: Mass Air Flow Sensor? (What is it??)

Hey guys,

I thought I would drop by and give you a DIY test for
that component.

Just the blah,blahs as follows;
One wire supplies power,a second for the ground and
a third for the signal.The other two are for the burn
off cycle when you shut your engine down(power and ground).

Test; function;
Start the engine and let it idle.The signal wire will
have a voltage between 0.25 and 4.75 volts.At idle the voltage should be low and as you increase the rpm's,the voltage increases.If this does not occur,
check for 12 volts between the sensor and ground.If cool do a resistance test and the readings should not be above 1000 ohms and if any higher replace.

Hope this little test saves you some money in the future[8D]Take it easy!Bye

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#9 (permalink) Old 09-09-2005, 04:55 PM
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RE: Mass Air Flow Sensor? (What is it??)

Thanks very much Greg! It is no longer a mystery!
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#10 (permalink) Old 09-10-2005, 11:32 PM
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RE: Mass Air Flow Sensor? (What is it??)

Quote:
mercedesc280car - 8/28/2005 2:17 AM

The hard shifts that you are currently experiencing are most likely caused by a bad mass air flow sensor. i.e. you go to acc. quickly the computer senses the incorrect air flow makes the fuel ratio too rich. then car trys to out drive itself (as if you were taking it to red line when in all actuality you are nowhere near it) then it goes to shift hard to carry the power into second gear hence the hard shift
Quote:
gregs210 - 9/3/2005 2:35 AM

You didn't mention miles but hard shifts can suggest a fluid change is in order. It's supposed to be a "lifetime" fill, but most folks seem to change it out, some argue about every 30K, average seems to be around 60-80K. However, the other post is correct, if the MAF sensor is tossing off inaccurate readings, the computer's attempt to compensate can alter shift points, etc.

Good luck and enjoy the ride,
Greg
Actually, try searching on this. Hard shifts are the tranny's way of warming up. Its quite normal on 95ish models.

You may have a problem if it is always hard, then you could try what the guys suggested
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