2.5TDI: Replace Hitachi LMM with Bosch HFM5

Hello everyone,

I have an EDC15 engine control unit here that I'd like to modify to use a Bosch HFM5 mass airflow sensor from an Audi S3 8L. This sensor is capable of handling flow rates exceeding 1050 kg/h. The currently installed Hitachi mass airflow sensor fails at 900 kg/h, resulting in a limp-home mode due to a "signal range" error.

Quote:

> I once measured the connector of the mass airflow sensor. Pin 1: 5.05V, 5.06V. Pin 2: 12.22V, 13.88V Pin 3, ground. Pin 4: 0.06V, 1.66V Pin 5: 1.31V, 1.91V The first value indicates ignition on, engine off. The second value is the engine speed at idle.

"On the LMM, it says:"
059 906 461G
Hitachi AFH70-25F

Quote:

Bosch HFM5 Ignition on (no airflow) 0.98 - 1.02 V - If the reading is outside this range, the hot film is contaminated. "When air is blown into the system at idle, the voltage should be between approximately 1.3 V and 4.2 V (with increasing airflow). If the value does not change, the membrane is likely ruptured." NTC: Setpoint at 18°C, resistance value 2.4 - 2.7 kOhms. 1 = Intake air temperature sensor. 2 = Supply voltage 12 V. 3 = mass 4 = Reference voltage 5 V. 5 = Signal

The Bosch HFM5 was used in the following engine control units (ECUs) with a 2.5 TDI engine. Can anyone provide values for these? In my opinion, it should be sufficient to swap pin 1 and pin 4 – or am I missing something?

(I know where the characteristic curve is located in the EDC15...)

P.S.: Through my own research while creating the poster, I may have already answered the question myself - but I'm still posting it - maybe it will help someone.

Okay, you probably already have the respective specifications. Hopefully, they are correct, because I seem to vaguely remember that the diameter of the pipe where the mass flow meter is inserted might have been different (70mm/80mm).
Please check this, otherwise the measurement results will be incorrect for the locus.

Best regards, Rainer.

If the original LMM, at 900 mg/hub, "gives up," then it's probably not originally intended to have a higher value, is it?
If you're going to do something, do it right.
hg
Herbert.

Hallo Rainer, danke für den Hinweis. I'll take a look.

I meant kg/h and I thought I had written that. The Hitachi also shows more than 900 in mg/h.

@Herbert:
"Who's talking about original hardware? It should be clear that the standard loader doesn't even come close to reaching its full potential of 900 kg/h..."

Okay .

@Frog: Just a silly question... since you're already messing around with the EDC15, why don't you switch the "opacity" setting to boost pressure?
The 900mg is sufficient for controlling the EGR valve.

Best regards,
Micha

The answer has 2 parts:
1. The signal range error still occurs and triggers a fail-safe mode. Disabling the error is not a solution.

"Calculating air mass based on temperature and pressure only works for a known system. If you have a GTB2262vkrl turbocharger on a 2.5 TDI engine, you don't know the engine's displacement (as it depends on the exhaust back pressure), nor do you know the pressure difference (delta_p) in the charge air system. That's where a mass airflow sensor (MAF) comes in handy. Sometimes, 100 mbar less boost pressure is better for engine filling than more boost pressure."

We're talking about almost 300 horsepower. And no, the fuel injection pump is not a standard part .
And again, it's about an air mass flow rate of 900 kg/h. The LMM (mass airflow sensor) measures in kg/h, while the EDC15 converts it to mg/h, depending on the engine speed. There is no known limit for mg/h (except for diagnostic/correction maps, which can be expanded).
However, the EDC15 cannot process sensor values from the mass airflow sensor (MAF) that are greater than 5V, and that is why it is sparking.

I will hopefully get back to you with the problem solved .

Okay, so we've now installed a new Bosch S3 LMM, and the characteristic curve has changed.
Now, the following error message appears, and the LMM values are incorrect.

So habe jetzt die LMM vor mir liegen auf dem Tisch. Und habe mal Widerstandswerte gemessen... Strange.

Hitachi LLM.
Pin 5 (signal) & Pin 1 (5V) = 0.010
Pin 5 (signal) & Pin 3 (ground) = 0.002.

Bosch LLM (legacy).
Pin 5 (signal) & Pin 4 (5V) = 0.359
Pin 5 (signal) & Pin 3 (ground) = 0.355

Bosch LLM, new.
Pin 5 (signal) & Pin 4 (5V) = 0.363
Pin 5 (signal) & Pin 3 (ground) = 0.358

The Hitachi LMM and the Bosch HFM appear to be electrically incompatible .

Unfortunately, I can't find the settings for adjusting blur via LD/LLT, nor can I locate the corresponding lookup tables. This isn't a problem with the 512KB EDC15 setups.

If anyone has any more information, any advice is welcome.

Hi,

"Um, Mr. Tuner, you won't get very far with resistance measurements in this case. The mass airflow sensors output a certain voltage as an output signal, and differences in internal resistance are likely to be insignificant given the existing circuitry."

Is there no measurement block in the control unit where you can see the raw voltage of the MAF sensor signal?
If in doubt, measure with a multimeter while the component is installed; unfortunately, you'll have to tap into the wires.
You can see from the diagrams of each LMM (lambda-controlled mass airflow sensor) whether the correct air mass is being measured, because in idle without EGR (exhaust gas recirculation), it should be a fixed value (approximately 480 mg/H).

Best regards, Rainer.

Hello,

Is there anything wrong with putting the original sensor into a larger housing? I've seen this done before with gasoline engines. For example, Treadstone offers air separators for such modifications.

Regards,
Jan.

The original mass airflow sensor (MAF) outputs 5V when the air mass being drawn in is at its maximum (full scale). Therefore, the engine control unit (ECU) interprets this as implausible and triggers a limp-home mode.

Idle voltage:
2.11-2.12v

According to the performance curve, the output is 60.8 kg/h at 750 rpm, which translates to approximately 440-450 mg/h. That's strange...

Where does the error message come from, if it should actually be able to perform meaningful analysis?

Hi,

At a 5V operating voltage for the mass airflow sensor, the maximum output value is limited to just below 5V. The engine control unit also expects this, and therefore interprets a voltage above this level as a "short circuit to 5V."
I would not change the corresponding threshold voltage. One option is to use a mass flow meter that can measure a larger mass of air.
It seems you're having trouble with the adaptation in the dataset; I suspect you're adjusting the parameters in the wrong places.
Then, as suggested by the previous poster, you could use a thicker pipe, but this might end up being a fiddly and complicated job.

My suggestion would be to log air mass, RPM, and boost pressure, and to run a log with a limited fuel injection amount and boost pressure.
Then you manipulate the LMM sensor, for example, by partially blocking the air intake openings on the sensor surface on the left and right sides (using a cover or similar).

Now, the mass airflow sensor (MAF) is "reading too low." However, you can use the log file you previously created, along with some test drives, to calibrate your data and diagnostic information to the new sensor.
For example, you can adjust the axis of the (rpm, air mass) characteristic curve and simultaneously modify the conversion factor for diagnostic purposes. While this method might not be as precise as using a suitable mass airflow sensor with adjusted data, it's unlikely to matter much if the characteristic curve becomes slightly non-linear in some areas.

I would definitely only adjust the VTG control using the corresponding characteristic map and avoid cross-references with the mass airflow sensor (MAF) map. Otherwise, the entire control behavior will quickly become undefined (rand(x).

And yes, you can do it the way Wiesel suggested, no, of course, you should NOT make the VTG control dependent on the air mass. Wiesel is actually very knowledgeable. Just get rid of the error message/emergency mode, make sure your loader is properly controlled without turbidity limitation, and then set the turbidity to a reasonable level.

If your turbocharger starts to surge, FIRST try to resolve it by reducing the boost pressure. Afterwards, you can adjust the VTG position and, consequently, the exhaust back pressure to extract a little more air mass and potentially more boost. This is an iterative process, and it will take several days for the boost control (KF) and VTG control (KF) to look reasonable. At the lambda control (KF), regardless of whether it's through air mass or boost pressure, you can adjust it when you are finished}}. However, it seems to me that the order of the steps is mixed up in your case?

Best regards, Rainer.

Is there anything new?