Dynamic testing of MAF - PeachParts Mercedes-Benz Forum

erubin · #1 09-14-2007, 04:01 AM

2000 430clk.
Got CEL P0170 and P0173. Likely suspect is the MAF. MB provided the following test. Place car in 3rd gear. Accelerate at WOT and record the MAF when engine hits 4000 RPM. For this car the MAF should show somewhere around 525kg/hr (from memory, don't remember exact figure). I measured 400kg/hr. car lacks power at WOT. Will replace the MAF because it failed the test. Idle is perfect (smooth) so vacuum leak is unlikely.

Before deciding to replace the MAF always try disconnecting and reconnecting the MAf (with engine off). Sometimes the contacts develop an oxidation layer that falses the readings. Reconnecting can "clean" the contacts. In my case it made no difference and I still read about 400kg/hr.

JimF · #2 09-14-2007, 10:29 AM

Try cleaning it . . check out MENU#4a . .

Arthur Dalton · #3 09-14-2007, 12:05 PM

....and check your air filter. too.

erubin · #4 09-14-2007, 01:28 PM

Air filter is new. Cleaning the MAF is a good idea but I've heard that the problem usually comes back if only a cleaning is done. I'm doing this for someone and don't want them coming back in a few weeks with same complaint. Have you had experience with cleaning and lasting results. Do you clean with aerosol, such as brake cleaner or do you use a swab and alcohol?

Arthur Dalton · #5 09-14-2007, 01:31 PM

I use CRC MAF cleaner ..aerosol.
Works great and fast/easy to use..

erubin · #6 09-14-2007, 05:29 PM

I cleaned the MAF with CRC electrical contact cleaner which is the same formulation as CRC's MAF cleaner. Results were negative. I then tried cleaning it with alcohol on a swab and got modest to no improvement. I replaced the MAF with a new Bosch unit and car is fixed! I'm measuring about 550kg/hr at 4000 RPM, 3rd gear WOT. This is what it should be.

btw, I've "fixed" a few Toyotas throwing lean codes by spraying the MAF but doesn't seem to work as well with these MB Bosch film type MAFs, at least in my limited sample group.

JimF · #7 09-14-2007, 07:08 PM

Quote:

Originally Posted by erubin

BTW, I've "fixed" a few Toyotas throwing lean codes by spraying the MAF but doesn't seem to work as well with these MB Bosch film type MAFs, at least in my limited sample group.

Same here . . in the three or so 'film' type that I've done, they didn't "stay" fixed but cleaning the older hot wire type works perfectly.

Eraser-X · #8 01-09-2008, 03:27 PM

I know this is an old thread but I am having an odd issue and want to rule my MAF out as a cause. I have a 02 E55 and I am getting -18% fuel trims (less then 1% difference left to right) with my new MAF module.

I have post my original question in this thread but I am not getting any answers

Fuel trim and fuel pressure questions/problems

Thanks

erubin · #9 01-10-2008, 05:09 AM

Attach your OBDII scanner and read the air mass flow measurements generated by the sensor at WOT in 3rd gear and at 4000 RPM. You'll have to shift the car into 3rd. You have to catch your reading at 4000RPM so you may want a helper to read the scanner just when you hit 4000RPM so that you can remain concentrated on the road while accelerating on the highway. You want to see a MAF reading that is about 550kg/hr or more. Convert 550kg/hr as needed to match your OBDII scanner's mass flow units. For example multiply 550 by 2.2 and divide by 3600 to get it into lbs/sec. That's all the help I can give you.

BTW, don't do this during rush hour! you need an open highway.

Just realized you have a different car so you need to get the spec for your engine. Any MB tech with access to MB specs should be able to give you this. I have a friend at the dealership who gave me this for the car I was working on.

gmercoleza · #10 01-10-2008, 07:35 AM

Quote:

Originally Posted by erubin

Attach your OBDII scanner and read the air mass flow measurements generated by the sensor at WOT in 3rd gear and at 4000 RPM. You'll have to shift the car into 3rd. You have to catch your reading at 4000RPM so you may want a helper to read the scanner just when you hit 4000RPM so that you can remain concentrated on the road while accelerating on the highway. You want to see a MAF reading that is about 550kg/hr or more. Convert 550kg/hr as needed to match your OBDII scanner's mass flow units. For example multiply 550 by 2.2 and divide by 3600 to get it into lbs/sec. That's all the help I can give you.

BTW, don't do this during rush hour! you need an open highway.

Just realized you have a different car so you need to get the spec for your engine. Any MB tech with access to MB specs should be able to give you this. I have a friend at the dealership who gave me this for the car I was working on.

Sorry to threadjack, but are you saying a standard OBDII scanner will give MAF readings? I don't recall reading that in my scanner's manual. I thought only SDS could provide adaptation values and you had to use a multimeter in conjunction with MAF manufacturer documentation?

erubin · #11 01-10-2008, 12:47 PM

I have a generic Actron OBDII scanner. I can read live data like trim, O2 signal, coolant temp, MAF etc. It's not a fancy scanner but it does have live data capabilities. I assume the previous poster can see it too since he mentioned trim values. Maybe some OBDII scanners are so cheap that all you can do is read the code and nothing else?

Eraser-X · #12 01-10-2008, 08:39 PM

Thanks for the quick reply I also have a Actron scanner the CP9145. I was really hoping for someone to be able to get me the spec for my car since I can not seem to find it in the WIS. I have also swapped the MAF with a couple of others and the only that one is reading the -18 to -20% so I am pretty sure it is bad. Now to see if GermanStar will warranty it.

Once again thanks for the quick reply

erubin · #13 01-12-2008, 02:36 AM

it's really too bad that no one on this site has read this and can give you the MAF spec value in mass/time at a specific RPM at a particular shift point. I do not believe that this spec is available in the FSM. I got it from a MB tech (friend) at a dealer that had access to this readily available technical info. With that info you could test your MAF. The trim values don't tell you the MAF real time measurements.

Is your car accelerating OK. Does it have full power. Why does changing the MAF change your trim values. Are you reseting the trim values each time you retest?

Eraser-X · #14 01-12-2008, 10:48 AM

When using the MAF that shows the -18 to -20% the car does not shift well or have a linear power band. So I was concerned right away and was just hoping for more information to give Germanstar for the return of the defective part.

Thanks

Eraser-X · #15 02-05-2008, 04:50 PM

Well guys got my hands on another MAF and was able to verify that it was a BAD MAF that was causing the issues. GermanStar took care of replacing the bad MAF very quickly and without any unneeded hassles.

I was not able to get the information I was looking for to complete the dynamic but I will keep looking for it and post it once I find it.