Why isn't the engine smoking so much?

Hello,

Today, I experimented extensively with replacing the mass airflow sensor (MAF) using a diode and logged data.
What was already foreseeable based on the quantity restrictions (Block was confirmed by Block 1:
At full throttle, the fuel injection volume is practically equivalent to the torque curve.
The soot limit is effectively disabled: The air mass reading constantly displays 1275 mg/hub, which is the highest value that can be represented with 8 bits at a resolution of 5 mg.

The strange thing about it is:
Even with full acceleration in 4th gear from just under 1200 rpm, where there was initially very little turbo boost pressure, no soot development whatsoever was visible in the rearview mirror, despite an injection amount of 38-42 mg (which may have been further increased by the 216 injectors!).

And that's despite the fact that you can clearly feel how the power builds up with the increasing boost pressure every time you accelerate, indicating that an initial lack of air is limiting the torque, even though the fuel injection quantity is practically at its maximum.

But wouldn't such an operating condition cause a complete blackout behind the TDI for minutes... (it was almost completely windless)?

Even with further similar attempts, and upon careful examination in the rearview mirror, nothing resembling soot could be detected.
The engine power is normal, so a lack of fuel cannot be the explanation for the "lack of soot."

Okay, no observations were made by a following vehicle – not even the "knife test" at night, which involves checking if anything is wavering in the beam of the following vehicle's headlights.

But this observation not only surprised me, but also seriously confused me.

Who can help me understand this riddle?

P.S.:
Despite using a diode instead of an MAF sensor and having the EGR system disabled, the AFN error memory remains clear.
And of course, all the attempts were made outside of public transportation areas...

Could you please display the voltage of the RWG instead of the MG values?

It's not that we think the EDC is making fun of us here.

If I start with a 10-cent throttle input, there's definitely some tactical camouflage involved. WITH HFM and WITHOUT AGR...

On the other hand, the electronic fuel injection (ECU) operates within a defined map. Regardless of what the high-frequency module (HFM) reports, at low engine speeds and without any boost pressure, the fuel won't be released.
At 1200 RPM, I have 30mg of fuel being injected within the torque limit and 27mg in the air mass measurement. So, there's not much difference between the two.

CU Gremlin.

Hello Ulf,

'The amount of fuel injected is determined based on the air mass calculated from factors such as boost pressure, engine speed, driver demand, and several correction maps. If everything else in the vehicle is within normal operating parameters, why should it produce excessive soot? The Mass Air Flow (MAF) sensor signal is used to calculate the Exhaust Gas Recirculation (EGR) rate and serves as an additional safety measure to limit smoke if there's a significant discrepancy between the calculated air mass and the measured air mass. However, this doesn't automatically mean that the car must produce soot when the smoke limiting function is disabled.'
You could save yourself the calculation! It might be a little more than that, but your observation from the rearview mirror is perhaps a bit too inaccurate .

Best regards,
Accelerator pedal.

Gremlin wrote:

Could you please log the voltage of the RWG instead of the mg values? not that the EDC is making a fool of us here.

Hi Ralf,
I already have that; block 1 includes the RWG voltage.

(rpm / mg / Volt):
1155 / 35 / 2.7
1596 / 39 / 3.06
1911 / 42 / 3.26
2499 / 41.4 / 3.5
3024 / 40.8 / 3.68

I think that sounds plausible if you translate it into a pump characteristic curve.

gaspedaluser wrote:

The amount of fuel injected is determined based on the air mass calculated from factors such as boost pressure, engine speed, driver demand, and several correction maps. If everything else about the vehicle is within the normal range, why should it produce excessive soot? The Mass Air Flow (MAF) sensor signal is used to calculate the Exhaust Gas Recirculation (EGR) rate and serves as an additional safety measure to limit smoke if there is a significant difference between the calculated air mass and the measured air mass. However, this does not automatically mean that the car must produce soot when the smoke limiter is disabled.

Hi.

"It seems the boost pressure isn't coming on properly, because if it were, the amount [of something] shouldn't exceed over 30mg when you press the accelerator, but the boost pressure is still almost zero."

From what air-fuel ratio does a TDI engine start to produce noticeable soot?

Let's assume, in the "worst-case scenario," we have 500 mg of air and approximately 38 mg of diesel (due to the larger nozzles), which results in a ratio of 1:13.2.

Hello,


'It seems the boost pressure isn't coming on properly, because if it were, the amount

The values are taken from a characteristic map. Not all areas need to be defined using the same criteria. In the area where there is still no significant boost pressure, a larger amount of fuel will likely be released relative to the air intake. Otherwise, you would have extremely poor acceleration. However, this can be clearly seen in the rearview mirror.


Let's assume, in the 'worst-case scenario,' we have 500 mg of air and approximately 38 mg of diesel (due to the larger nozzles), which results in a ratio of 1:13.2.

Why not? A lambda value of 0.9 seems possible for dynamic processes to me.

Best regards,

Hello again,

This morning, I made a few more attempts, but without any real-time data logging.
The low-hanging sun behind them allowed them to see the smoke clouds almost as clearly as they would in darkness, illuminated by the headlights of the vehicle following them.

Attempt 1:
"The LMM (mass airflow sensor) has been replaced with a diode (as previously described). Now, when accelerating hard from low RPMs, a haze was visible in the rearview mirror for as long as it took for the turbocharger to build up boost."
In previous attempts, something similar likely happened, but the higher position of the sun in the sky prevented the soot from being noticed.

Attempt 2:
Disconnected the hose from the VTG unit, which meant that (almost) no boost pressure was generated. This resulted in a significant loss of power (finally), and also produced the expected thick cloud of black smoke as long as acceleration continued.
The maximum charging pressure in the test, approximately 0.2 bar, was only reached at 3,000 rpm.

Attempt 3:
The VTG (Variable Turbine Geometry) and LMM (Lambda Measuring Module) have been reactivated. Now, even at full throttle with the engine running at 1100 rpm in direct sunlight, no more traces of black smoke could be seen.

Experiment 2 has proven that boost pressure (at least in the case of the AFN engine) does not play an immediate role in calculating the fuel injection amount.
As soon as the LMM signal indicates sufficient air is present}, the corresponding fuel injection amount is released during acceleration, even if the boost pressure is practically zero.

If the engine control unit (ECU) were to directly use the boost pressure for calculating fuel injection amounts, it should have reacted to the "faulty" variable geometry turbocharger (VTG) by reducing the fuel injection amount accordingly and suppressing black smoke emissions.

This observation aligns with the air mass injection limit set by VAGCOM when replacing the MAF sensor with a diode: even without boost pressure (in overrun mode), the air mass limit is around 40 mg.

The boost pressure control system essentially operates "alongside" the fuel injection calculation – acting more like a tool to provide sufficient airflow so that the fuel injection quantity requested by the accelerator pedal can be released.

Hello Ulf,

Ask me before you make wild measurements!

The amount of fuel injected is primarily limited by the torque map! However, as you correctly pointed out, if the air mass is too low, resulting in an injection quantity calculated from the torque that would lead to smoke emissions, the smoke limiting map intervenes. This map has engine speed on the x-axis, injection quantity on the y-axis, and the permissible injection quantity on the z-axis.
The boost pressure primarily therefore has no influence on the fuel injection quantity, but only on the air mass! Of course, if I don't have the desired boost pressure (Attempt 2), I also don't have enough air mass, and the fuel injection quantity is limited. So, the boost pressure secondarily does have an influence, but it doesn't enter as a value into the control unit for calculating the fuel injection quantity!

Determining the smoke density field requires numerous measurements using an opacity meter, and it is not easily calculated on a computer due to the influence of dynamic factors.

Best regards, Ben.

Ben1972 wrote:

. . .hits the smoke reduction map. This map has engine speed on the x-axis, injection quantity on the y-axis, and the allowed injection quantity on the z-axis.

Hi Ben,

Is this a new version of the software?
I'm only familiar with it using the axes of engine speed, allowable fuel injection amount, and air mass.

Otherwise, thank you for your confirmation .

Laugh, that was a Freudian slip; I meant x: DRZ, y: LM, and z: ME.