TDI Throttle Body: Problems & Solutions

Hello VW enthusiasts,

'For days now, I've been thinking about getting a speed limiter installed in my TDI (because of my father, who always drives too fast, even when the engine is cold).'

It should definitely be an option to enable this, just like a 10-cent tuning. I asked about this a few days ago, but I haven't received an answer yet.

I would really appreciate any tips you might have, as they could help me keep my TDI running for a bit longer.

Best regards,

Hi Tim,

Try connecting a resistor in parallel with the RWG reference coil, specifically between pin 1 and pin 2, while the motor is running.
Start with 1 kOhm and then gradually decrease the value, just like with 10c tuning.

No idea if it will work, but theoretically, it might be possible.

Quote:

Because of my father, who always drives very fast, even when the car is cold.

Whether that will matter if you're pushing the machine to its absolute limit with a chip and 10c .

Deleted upon request.

diesel.gustav wrote:

... but he keeps adding more and more junk to his pump. And he probably doesn't yet know what happens when the control unit no longer recognizes or accepts the HDK signal due to a short circuit or interruption in one of the two circuits.

Hi Gustav,

what could possibly happen... except that the EDC might shut off the engine at the most inopportune moment.

Do you happen to know any more details about the HDK signal processing in the engine control unit?
It has already been reported that a 10c tuning (in parallel with the measuring coil) using antiparallel diodes in series with the resistor seems to selectively emphasize the higher RPM range, while a resistor without diodes provides a more even increase in power. This can lead to severe vibrations below 2000 RPM with aggressive tuning.

For both of these, we haven't yet found a truly convincing explanation.

Hello Ulf, Gustav,

During my attempt to replace the 10C Tuning Alpine box, I tried the following configurations:
- antiparallel 1N4148 diode + potentiometer
- 2 antiparallel 1N4148 diodes + potentiometer.

During the subsequent test runs, I observed that the injection quantity at full load remains approximately constant with increasing engine speed, while the control valve voltage increases under the same conditions.
This explains the greater performance gain in the higher RPM range, which was particularly noticeable with 2 antiparallel-connected diodes.
I am unsure why the RWG pressure is increasing, because with the same injection quantity, it should rather decrease with increasing engine speed due to the lower leakage losses in the pump .

@Gustav: Could it be that, due to a lower filling level of the pump element in the ESP (Exhaust Gas Recirculation system) at high engine speeds, the EDC (Electronic Diesel Control) compensates by using a stronger control signal to the mass airflow control valve? The engine speed at which the RWG (Rear Wheel Glide) voltage noticeably increased wasn't particularly high, roughly around 3000 rpm.

Best regards, Rainer.

Rainer K. wrote:

During the subsequent test drives, I noticed that the injection quantity at full load remains approximately the same with increasing engine speed, while the control valve voltage increases under the same conditions. This explains the greater performance gain in the higher RPM range, which was particularly noticeable with 2 antiparallel-connected diodes.

Hi Rainer,

That's funny... I always thought that the EDC considered the RWG signal as a direct measure of the control slide position and, therefore, the feed rate, which should thus be unchangeable in the software (except when adapting channel 1).

Quote:

@Gustav: Could it be that, due to a lower filling level of the pump element in the ESP at high speeds, the EDC (Electronic Diesel Control) compensates by using a stronger control signal to the mass flow meter?

What could cause a low filling level? Could the higher intake speed towards the high-pressure chamber "dilute" the diesel fuel, or could it create steam bubbles or something similar?

Hello Ulf, Tim,

Quote:

I always thought that the EDC considered the RWG signal as a direct measure of the slide position and, therefore, the conveying volume.

I thought so too!

Quote:

Where could a low filling level come from? Could the higher intake speed towards the high-pressure chamber cause the diesel to be "diluted" or create steam bubbles, etc.?

Have you ever drawn up a syringe before? Whether the effect plays a role at the mentioned speeds is, as I said, just speculation on my part; honestly, I personally find it unlikely. Maybe Gustav knows more about this...

@Tim: A 0C solution would be a cork, carefully carved to fit as a stop for the accelerator pedal.

Best regards, Rainer.

Deleted upon request.

Hi Gustav and Rainer,

So, as far as I understand it, the mystery surrounding the "discrepancy" in the VAGCOM readings for RWG voltage and fuel injection quantity remains unresolved for now.

It seems to me that the EDC not only evaluates the AC signal voltage at the RWG, but also the signal shape: The diodes, after all, clip the AC peaks.

Of course, the motor speed has no direct influence on this process.
If the EDC still reacts speed-selectively, then it seems to me, in the final analysis, that a "suspected" (but actually non-existent in the VP 37) filling deficit of the high-pressure chamber is being compensated for, because that would be, in my opinion, the only sensible explanation for the "strange" behavior of the EDC when diode-tuned compared to tuning only with a resistor.

Hello Gustav and Ulf,

Quote:

So, the mystery surrounding the "discrepancy" in the VAGCOM readings for RWG voltage and fuel injection quantity remains, as far as I understand it.

I realized that I didn't pay attention to the fuel temperature during the measurement...
I will re-record the measurements at a later date.

Best regards, Rainer.

Rainer K. wrote:

I realized that I didn't pay attention to the fuel temperature during the measurement... At the appropriate time, I will re-record the measurements.

Hi Rainer,

if the "puzzle" can be turned on and off using diode tuning, then the test regarding the diesel temperature becomes unnecessary .

Hi,

What would be the electronic extension of Rainer's cork?

Depending on the operating principle of the electronic gas pedal, a switchable resistor can be connected, for example, in series with the throttle potentiometer.
That should be enough to slow down the "heater daddy."

It's funny, my daddy always complains when I accelerate. But at least I wait until the engine is warm .

Hi Ulf,

Quote:

However, if the "puzzle" can be turned on and off using diode tuning, then the test related to diesel temperature may become unnecessary.

"However, it doesn't explain why the RWG voltage doesn't increase even when the injected fuel quantity remains constant. This should be independent of any diodes or other components."

It might be related to the pump characteristic curve that Gustav mentioned, and it's possible that my fuel warmed up faster in the ESP. The question is, which parameter has what influence?
Therefore, I would like to rule out the possibility of a changing fuel temperature, because otherwise my measurement might have been a coincidence.

Best regards, Rainer.

Roger wrote:

Depending on the mode of operation of the E-gas, a switchable resistor, for example, in series with the throttle potentiometer.

Hi Roger,

This could also backfire: the EDC expects the idle contact to switch within a specific (lower) range of pedal sensor voltage.
If this relationship suddenly no longer holds true due to electronic interference, the accelerator pedal is recognized as defective, and you may have to limp to the next workshop with an idle speed of 1200(?) rpm .

But with that, Tim's goal would be perfectly achieved .

Hello,
I had the same thought about the potentiometer on the accelerator pedal position sensor, but I was concerned that it might be recognized as a fault, as Ulf mentioned.

I tried 'throttling' using resistors (potentiometers) and came to the following results.

It took me approximately 8.6 seconds to go from 2000-4000 RPM with a 400 Ohm load, which, according to a dyno calculator, would be about 103 horsepower.

370 Ohm ~8.76 seconds. ~ 101 horsepower, although the engine produces significantly less power below 2000 RPM.

340 Ohm ~ 9.17 seconds ~ 97 horsepower, but with very little power available below 2000 RPM, so you have to give it a lot of gas just to get it moving. However, above 2000 RPM, the engine suddenly develops a lot of power, making it difficult to drive smoothly.