Hello to all,

I post my message here to have feedback of specialist of the M112 engine.
I own a SLK 32 AMG.

Issue I have is a suddenly decreasing of the power after 5200rpm.
With log and my dashboard, I see my mass air flow decreasing from 292g/s to 220g/s.
- My MAP stays around 244kpa
- My IAT is around 55degreesC
- My throttle has been changed

So, my question is how is calculated the mass air flow ?

Thank you for your help,
Julio

Julio,

I think you have M112K Engine, which does not have "MAF",

calculate MAS should be through "MAP" sensor, and sensing the MAS tmp. via "IAT" sensor isn't..?!!?

ZAYED,,

Did you diagnose the car, codes will help..!

ZAYED,,

Hello Zayed,

You're right M112K.

Yes, no MAF in this engine and I would like to know the calculation of the mass air flow.

I saw MAF in real time in my dashboar, so the engine is able to calculate it. I guess with MAP, IAT and throttle body position. But is there any other sensors to calculate ?

I have no code...

Thanks,
Julio

You also need the pressure in front of the Throttle body that is inferred from the Barometric pressure minus loss through the intake system.

Then, it's calibrated through the volumetric efficiency of your engine, so, no, you don't have an easy way to calculate your MAF without knowing the how it has been calibrated or knowing the VE of your engine.

What is your engine load -value in full throttle? At least Star diagnostic is able to display it.

I maybe have little bit same problem...

If you’re asking about your engine’s theoretical airflow, assuming you’re running at sea level, 90% volumetric efficiency, with 14.5 psi of boost, at 6220 RPM (that is your redline, right?) your engine is moving 627 CFM. You’re probably closer to 85% volumetric efficiency, which would set you at 589.

BTW, you'll always need to know RPM to guess air flow (and without a MAF, it's a guess). Intake manifold pressure, throttle position and air temperature alone won't do it. Here's an example of why - If an engine is at wide open throttle with 2 atmospheres of pressure in the intake manifold, at 2000 RPM, it's moving a lot less air than if it's at 6000 RPM under the same conditions. Yet the pressure, throttle position and air temperatures are both the same.

I have this kind of issue, my ecu is showing ~130% engine load in full throttle and over 5000rpm. And then my AFR starts to bounce up and down.

I know my ecu maps what uses the load value, there is only 112% max value. So im out of maps/charts, correct?
If i clamp my boost to be less, then my load value stays below 112%(below chart max value) and engine runs great.

So this issue must be about ecu maps/charts, or have to change something what calculates engine load value, air mass flow etc.

Am I on the right path?

Hello Guys,


Thank you for your answer.

To give you more precisions :

- 2nd gear : WOT. >No problem of power. Mass flow goes to 333g/s at 6000rpm
-3rd gear : WOT >: mass air flow goes to 297g/s at 5000rpm. After issue power and suddenly MAF goes down to 230g/s until the rev
-4th gear : idem
-5th gear : idem

What can affect the mass air flow calculation ?
IAT new, crank sensor new, throttle body new, 02 sensors new…


Can the pedal sensor be affect like this one - always ate the same rpm ?
Is there any other sensors to watch on the air loop ?

Thank you for any ideas to help me to solve this problem.

Regards,
Jules