What if you MAF reading in g/s?

Benz2021

Member
Joined
Sep 26, 2021
Messages
11
Reaction score
3
Your Mercedes
C class w203
Hello to you all,

I wanted to understand what is the usual reading of a MAF sensor on your car? There seems to be no data on this anywhere. Most people have OBD readers that can tell you what it is with live data. This should help anyone trying to determine if their MAF is bad (like me ).

Mine is below.

MAF READING
11.4 g/s at idle
W203 220 CDI OM646
 

mioba

Senior Member
Joined
Feb 19, 2006
Messages
8,263
Reaction score
4,976
Location
Nottingham and Köln
Your Mercedes
W124/E200, W220/S320CDI, W205/C200, W251/R350CDI 4Matic
bit confused. any reading will depend on the unit you use.

you can measure in inches, or cm etc etc

The reading unit can be changed surely in the instrument you are using.
 
OP
B

Benz2021

Member
Joined
Sep 26, 2021
Messages
11
Reaction score
3
Your Mercedes
C class w203
  • Thread Starter
  • Thread starter
  • #3
Sorry I believe the units is measured in grams/second on most tools so assuming the reading is in g/s what is the number on your car? I have read where it says at idle it should only be a few g/s. I have attached a screen shot of my OBD app to help.
 

Attachments

  • Screenshot_20220212-183311_Video Player.jpg
    Screenshot_20220212-183311_Video Player.jpg
    107.3 KB · Views: 6

alexanderfoti

MBO Forum Supporter
Authorised Forum Supporter
Joined
Mar 25, 2010
Messages
15,376
Reaction score
6,770
Location
Tonbridge
Your Mercedes
W221 S65 AMG - W204 C63 AMG + Various other MB's
That is about right for idle speed
 

bladecrazy

Senior Member
Joined
Jun 2, 2020
Messages
500
Reaction score
464
Location
bolton
Your Mercedes
tesla model 3 performance /honda cd175/w123 300d gertrude.
I thought it should be around 2gs at idle , my wifes c220 was around 2gs at idle and would rise with revs.
 

alexanderfoti

MBO Forum Supporter
Authorised Forum Supporter
Joined
Mar 25, 2010
Messages
15,376
Reaction score
6,770
Location
Tonbridge
Your Mercedes
W221 S65 AMG - W204 C63 AMG + Various other MB's
It will change depending on whether the egr is open or closed. Is there a problem that you are trying to track down?
 

bladecrazy

Senior Member
Joined
Jun 2, 2020
Messages
500
Reaction score
464
Location
bolton
Your Mercedes
tesla model 3 performance /honda cd175/w123 300d gertrude.
also my mb11 reads the maf in gs.
 
OP
B

Benz2021

Member
Joined
Sep 26, 2021
Messages
11
Reaction score
3
Your Mercedes
C class w203
  • Thread Starter
  • Thread starter
  • #8
I have a boost issue. Specifically high boost I have another thread going about it (W203 220 CDI LIMP MODE SUSPECT TURBO ACTUATOR) and I'm thinking maybe the MAF is the problem?

Bladecrazy this is what I'm thinking. Someone said before it should be around what the litre of the engine is. I.E. 2 litre is 2g/s 3 litre 3g/s
 

Doug1234

Senior Member
Joined
Jun 28, 2009
Messages
948
Reaction score
263
Location
Bedfordshire uk
Your Mercedes
1997 w210 e300td
Surely engine breather feeding into inlet can affect these readings though
 

bladecrazy

Senior Member
Joined
Jun 2, 2020
Messages
500
Reaction score
464
Location
bolton
Your Mercedes
tesla model 3 performance /honda cd175/w123 300d gertrude.
is the car smokey? if you have a reading its generally not the maf maybe something along the intake system.
 

M80

Senior Member
Joined
Jan 21, 2006
Messages
6,099
Reaction score
2,878
Location
Derbyshire
Your Mercedes
2014 639 Viano- 651, 5sp Auto. 2009 S211- 646, 5sp Auto.
This is where Star diagnosis wins.
Live reading will show as within parameters or not, the Torque app doesn't know.

Torque is v handy, and can even show many fault codes. Are there any codes on the fault page?

Your location might be handy for when you're looking for a local Indie.
 
OP
B

Benz2021

Member
Joined
Sep 26, 2021
Messages
11
Reaction score
3
Your Mercedes
C class w203
  • Thread Starter
  • Thread starter
  • #12
So car isn't smokey and faults are in in the other thread with extensive trouble shooting performed. I have found videos on you tube (admittedly not of merc) but all MAF readings seem to be alot lower (the litre of the engine seems to be the rule of thumb of grams/second) so my 11 g/s is much higher.

I have change the air filter (first thing I did when I got it) I think I'll monitor my MAF reading this week and if it gets worse (it was 24 g/s before cleaning it) I think ill change it.

Location is Bromley.
 

supernoodle

Senior Member
Joined
Sep 7, 2021
Messages
421
Reaction score
353
Your Mercedes
E220 2005 2.1D
2 to 3g/s must be for a petrol. They are fundamentally different to a diesel. Petrols throttle, Diesels don't (yes there are exceptions)

You can calculate an approx figure

Volume of theoretical air per second in cm3 is

Cyl vol[cm3] x RPM x no. of cyl/ (2 x 60)

Convert that volume to a mass assuming

Density of air @15degC in g/cm3 is 1.225 x10^-3

For a 2 litre at 800 rpm

500 x 800 x 4 / (2 x 60) = 13333.33 cm3/s

Multiply by density

1.225 x 10^-3 x 133333.33 = 16.33 g/s

That's theoretical, so assuming the engine has a volumetric efficiency of 90% gives

16.33 x 0.9 = 14.7 g/s

As mentioned, EGR will reduce this. So if active maybe reduce this by upto 50%.
You really need to make sure EGR is closed when checking.

Different air temps will change this too.
Also doesn't account for boost, so only good for idle. But it shows 2-3 g/s can't be correct.
 

Doug1234

Senior Member
Joined
Jun 28, 2009
Messages
948
Reaction score
263
Location
Bedfordshire uk
Your Mercedes
1997 w210 e300td
Plugged my icarsoft into my 0m642 3.0 crd in Jeep and got 13.9-14.4 at a tick over of 600rpm at 16deg c intake temp (8c outside) with engine half warm …. This only has a single maf and the one air filter box.
 

bladecrazy

Senior Member
Joined
Jun 2, 2020
Messages
500
Reaction score
464
Location
bolton
Your Mercedes
tesla model 3 performance /honda cd175/w123 300d gertrude.
petrol and diesel must be different, looks like diesels run at a higher gs than petrols.
 

LostKiwi

Senior Member
Joined
Aug 25, 2006
Messages
31,521
Reaction score
21,968
Location
Midlands / Charente-Maritime
Your Mercedes
'93 500SL-32, '01 W210 Estate E240 (RIP), 02 R230 SL500, 04 Smart Roadster Coupe, 11 R350CDi
petrol and diesel must be different, looks like diesels run at a higher gs than petrols.
As mentioned by supernoodle a petrol engine has a throttle plate limiting air flow.
A diesel usually (but there are exceptions) doesn't so is trying to get a full cylinder fill of air on every induction stroke.
This is why petrol engines have manifold vacuum and diesels don't (ignoring turbo chargers).

Diesel engines control engine speed by varying the fuel injected. Petrol engines control engine speed by varying air input and adjusting fuel to match.

Because of this air drawn in will vary only with rpm on a diesel (and the effects of EGR and PCV). On a petrol it will vary by both throttle position and rpm.
 

WE HAVE NOW MOVED: 8 Hazel Road, Woolston, SO19 7GB
Service, Repairs and remapping service
Any queries, please do not hesitate to contactEmail@mbsofsouthampton.co.ukor alternatively you can phone Colin or Dave on 02380 445820, out of hours numbers are 07787913313 or 07907631681.
Top Bottom