Replacing a Hitachi LMM with a Bosch HFM5 on a 2.5 TDI engine

Hello everyone,

I have an EDC15 engine control unit and I would like to install a Bosch HFM5 mass airflow sensor from an Audi S3 8L. This sensor can handle 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 to 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 sensor is likely contaminated. "When air is blown into the system at idle, the voltage should be between approximately 1.3V and 4.2V (increasing with increasing airflow). If this 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: 12V. 3 = mass 4 = Reference voltage 5V. 5 = Signal

The Bosch HFM5 was used in the following engine control units (ECUs) with a 2.5 TDI engine. Can anyone provide any values for these ECUs? 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 within 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 anyway - 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 was different (70mm/80mm).
Please check this, otherwise the measurement results will be incorrect for the locus.

Best regards, Rainer.

If the original LMM (likely referring to a medical device or measurement) stops working at 900 mg/hub, then it's probably not designed to handle a higher value originally.
If you're going to do something, then 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 .

@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/hour..."

Okay .

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

Best regards,
Micha

The answer has 2 parts:
"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 installed on a 2.5 TDI engine, you don't know the engine's displacement (as it depends on exhaust backpressure), nor do you know the delta_p (pressure difference) in the charge air path. That's where a mass airflow sensor (MAF) comes in handy. Sometimes, 100 mbar less boost pressure is better for filling the engine 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 (air mass meter) measures in kg/h, while the EDC15 converts this to mg/h, depending on the engine speed. There is no known limit for mg/h that I am aware of (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 therefore it malfunctions.

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

Okay, so we've now installed a new Bosch S3 LMM (mass airflow sensor), 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

New Bosch LLM.
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 switches for adjusting blur via LD/LLT, nor 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 device is still installed; unfortunately, you'll have to tap into the wires.
You can see from the diagrams of each individual mass airflow sensor (MAF) whether the correct air mass is being measured, because in idle without EGR, 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, especially with gasoline engines. For example, Treadstone offers air deflectors for such modifications.

Regards,
Jan.

The original mass airflow sensor (MAF) outputs 5V when the air intake is at its maximum (full load). Therefore, the engine control unit (ECU) considers this value to be implausible and triggers a limp-home mode.

Idle voltage:
2.11 - 2.12 volts.

According to the performance curve, it produces 60.8 kg/h at 750 rpm, which is 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 an excessively high output voltage 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 amount of air mass.
It seems you're having trouble with the adaptation in the dataset; I suspect you're adjusting things in the wrong places.
Then you could use a thicker pipe, as suggested by the previous poster, but that might turn into a fiddly and complicated DIY project.

My suggestion would be to record air mass, RPM, and boost pressure, and then run a test with limited fuel injection and boost pressure while recording the data.
Then you manipulate the LMM sensor, for example, by partially blocking the air intake openings on either side of the sensor surface (using a shim or similar).

Now the mass airflow sensor (MAF) is reading "too low," but 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 MAF 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. By the way, Wiesel is 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.

Wenn Dein Lader anfängt zu pumpen, ERST versuchen mit weniger Ladedruck das in den Griff zu bekommen, danach kannst Du mit der VTG-Stellung und damit auch dem Abgasgegendruck spielen, um noch etwas mehr Luftmasse und evtl. möglichen Ladedruck heraus zu kitzeln. Das ist ein iterativer Vorgang und es wird einige Tage dauern, bis Ladedruck-KF und VTG-KF vernünftig aussehen. Am Trübungs-KF, egal ob per Luftmasse oder Ladedruck, kannst Du drehen wenn Du fertig} bist. IIt seems like the order of the steps in your workflow might be mixed up.

Best regards, Rainer.

Is there anything new?