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.

 

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..

 

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!

 

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

 

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?

 

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

 

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

 

Thanks very much Greg! It is no longer a mystery!

 

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

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

 

yusuke280 - 6/27/2005 9:44 AM

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,

If it ain't broken don't fix it.

The autos on these cars shift hard, especially from 1-2 shift. Especially when cold.

Don't replace MAF unless you have a problem with it.

There is no set interval to change it unless you like to waste money.

Transmission fluid change is usually around every 30k.

Sounds like the car is running like a normal Benz to me.


Since your parents never really drove it, the best thing you can do for it right now is to DRIVE IT. Take it on a long trip non stop and let it blow all the cobwebs out of the system. Set the cruise at 80 and drive non stop for a couple of hours. It'll be the best thing for a car that has been sitting.

 

FYI the MAF in a c230 is the "hot wire" as opposed to the "vane meter" type. It works by measuring the voltage required to heat a wire in the path of the airflow to a certain temperature and then calculates the density and flow rate of the air and adjusts the fuel/air mixture accordingly.

Recently I was pulling out of a parking lot when my car ('99 c230k) started bucking and died. it wouldn't restart no matter what i did for about 15 minutes. Then, all of a sudden, it cranked up no problem - but the engine light was on. I took it to the dealer and it was throwing a bad MAF fault code. As more of a motivation to do it yourself (which I will next time), it cost me over $700 to have the MAF replaced at the Mercedes dealership! At least I know it was done correctly and it has a warranty.

 

The labor on a MAF replacement takes about a minute. A screwdriver is typically used, but all can be done by hand, one clip, one clamp, one screw off wire conection, done.

 

i have a 1998 c230 w/ 140k miles, i have owned it for around two months and am not sure if the performance has gotten worse because i have just started driving it.. But, sometimes when im driving/pressing the gas. it starts to feel like i am barely holding down the break. There are the regular hard shits from 1st to 2nd.. but another thing i notices is when i am at a complete stop and accelerate it takes like 2 seconds for the car to get the idea that i am pressing the gas.. Another problem I have had is stalling or shaking when i come to a complete stop but i dont know if the MAF would control that or not.. basically i am wondering if any of these symptoms sound like problems with the MAF since it is a widespread problem.

 

I experience this? ANy thoughts?

 

TheMadMidget - 11/15/2005 9:14 AM

The labor on a MAF replacement takes about a minute. A screwdriver is typically used, but all can be done by hand, one clip, one clamp, one screw off wire conection, done.

Mine doesn't even require a screwdriver.

My 12 yr old son could do it in about 30 seconds.

700 bucks at the dealer......[!] Gimmie a break!

 

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?

I hope you were ablet to find the MFS by now. If not, on an 1997 C280 is is between the air filter and the intake maniford. As you look at the car, the air filer is to your left, just follow the output and you will see a small section that can be removed, maybe 4 inches long or so. You wil see a black cable that rides on top of the air intake duct and plugs into this. You can unscrew the entire section and use a cleaning solution. Also make sure to replace your air filter.

 

LOL, cleaning the dust off from old threads huh?

 

Hahaha, I love it. Actually, this is a good thread to have near the top, because it addresses what is quite possibly the only major and nearly universal problem that these cars have (bad MAF's and bad wiring harnesses).

 

Wiring Harness

what is the deal with the wire harnesses it is almost to the point it should be a recall. i have been told every service for the last 3 years (all different shops) that my wire harness is fragile and should be replaced. which there is no advantage to doing unless it is broke. my latest issue baffled my most recent repair shop and is currently boggling the minds of my local mbz dealer. i have 1997 c280 with 70,000 miles and under heavy acceleration from a stop the 5000 rpm rev limiter turnes on when the car is in drive. from what the 2 shops are telling me is that they have never seen this as an issue. the car runs fine if i keep it under 5000rpm but when it hits that it is really it stops accelerating begins to chug and will no longer shift.

 

what is the deal with the wire harnesses it is almost to the point it should be a recall. i have been told every service for the last 3 years (all different shops) that my wire harness is fragile and should be replaced. which there is no advantage to doing unless it is broke. my latest issue baffled my most recent repair shop and is currently boggling the minds of my local mbz dealer. i have 1997 c280 with 70,000 miles and under heavy acceleration from a stop the 5000 rpm rev limiter turnes on when the car is in drive. from what the 2 shops are telling me is that they have never seen this as an issue. the car runs fine if i keep it under 5000rpm but when it hits that it is really it stops accelerating begins to chug and will no longer shift.

A bad wiring harness can cause all sorts of poltergeists to appear in your car. Most reputable shops won't even start troubleshooting a problem until they know that the harness has been replaced.

Yes, Mercedes should have recalled the part, but they didn't and most likely never will. For a time, if your car had less than 100,000 miles many dealerships would cover anywhere from 50% to all of the cost of replacement, but these days I don't know of any that still do that. They much prefer you pay for the parts and labor (can be ~$2,000), or better yet sell you a new car.

 

cost

does anybody know how much it cost?

 

how much does it cost c280 99

 

One guy on ebay is selling them for $119 plus shipping. Expect $300ish for the par alone elsewhere. No experience with the guy though. For that price and with a decent feedback rating, I would be tempted.

My $.02,
Doug

 

Hey guys,


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).

Please comment on the wire positions. Are you referring to numbers 1 to 5 on the numbered connector pins?

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

Is the resistance to be measured between the two sides of the MAF wire or between 2 specific pins of the connector?
Which ones?
How to measure voltages with the MAF connected ? Do you mean mesuring them with it disconnected - in the MAF cable?
Thanks in advance. This is great guidance!
Jorge

 

I, too, wish somebody would comment on how to test while the MAF is connected. It doesn't look like you can pull the wiring cover back or that there are any access holes to the wires (unless I am missiong something). Maybe the original poster assumed the reader would have one of the semi-advanced scanning tools (SnapOn, Carsoft, etc.)? A basic OBD II scanner isn't going to be of much help.

FYI - Just in case anyone can tell us how to test, I will insert a diagram for the pinouts for the connector at the bottom of this post so that you will already have that piece of the puzzle

Here is a link to the entire document and to some more diagnostics:

http://www.x-desk.net/ximages/21302_pgsi0079en.pdf

Of course, until we know how to connect in to test things, it will still be a mystery!



Doug

 

MAF signal output testing

I, too, wish somebody would comment on how to test while the MAF is connected. It doesn't look like you can pull the wiring cover back or that there are any access holes to the wires (unless I am missiong something).

Has anybody tried putting a voltmeter across the MAF signal output wires at the ECU/fuel controller terminal where the wiring harness terminates into the large square plug on LHS of vehicle? Remove the black lid covering the computer. The corresponding wires are yellow/green and brown, coming off MAF plug pins 5 and 3 respectively. Insert DVM leads through top of plug onto wire terminals. I tried mine while engine running, got like 1.4V up to 2.0 odd volts at high RPMs. I thought this signal was supposed to reach a higher value like 4-5V DC. Sound like a failing MAF sensor? I've cleaned it, no change. Suggestions? Currently run the car with sensor disconnected for it runs best.

 

When I install my new MAF sensor should I disconnect the battery first so that the ECU makes adjustments for the new sensor?