Engine Stalls When Clutch Is Pressed

Hi there,
Problem description: My engine (1Z) stalled twice in quick succession while I was rolling and had the clutch depressed (possibly also during disengagement). It restarted both times, but in one case only after several attempts.
I have checked:
- Error memory of the control module (MSG): no entries found.
- Measurement block 6, value 2 (switch): The bit for the clutch pedal switch changes normally, the bits for the brake pedal switches change normally, with a slight difference.
- Measurement block 2, value for accelerator pedal position: behaving normally.
- All values for temperatures, air parameters, and injection are completely normal.
- Measurement block 12, value 3 (supply voltage): provides different values, with the ignition on, in the range of 10.5 V to 11.8 V.
- Battery voltage is okay (12.5V, 14.2V at idle).
- Cables connected to the battery are secure, as are those connected to the alternator.
- Mass connectors between the motor and body: are securely connected.
- Connection to the shut-off valve: is secure.
- Surge protection relay (J249):
The contacts of the open relay close unevenly under finger pressure, and the connection between terminals 30 and 87a exhibits a delayed response with some residual resistance (in Ohms).
With the relay plugged in, there is a voltage of 12.2V at contact 87 and contact 87a when the ignition is on.
Tapping the relay with the handle of a screwdriver has no effect.

The most likely culprit is primarily the clutch pedal switch, followed by relay J249. However, the behavior observed during testing doesn't provide much clarity. My diagnostic tool isn't reporting any error messages for the pedal switch.
The voltage values in MWB 12 are a bit surprising to me, but my RLF doesn't provide any information on that.
Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
Herbert.

Hello Herbert,
I don't have the wiring diagram for the Audi A4 here right now.
Has he already installed relay 109 (or something with the same function)?
"Regarding this (at least with the MSA15), it measures something internally."
Voltage at MWB 12.
The fluctuating values are consistent with contact issues.

Best regards,
Micha

Mechanisch ist alles OK, zB. KW-wheel?
Does the engine speed drop when you depress the clutch pedal while the car is stationary and in gear?
One possible candidate would be the pilot bearing, which gradually reduces the engine's speed.

Hello,

Is the mass airflow sensor (MAF) okay?

Best regards, Rainer.

Hi,
Thank you for your responses; I will address them in order.
- The J249 module has the function of the "J109," meaning that it activates the fuel injection system based on a signal from another component (MSG).
- Mechanically, everything is okay. - The drive pinion is tight, the driven gear is tight, and the electronic zoom potentiometer (EZP) is stable at the last set value.
- The engine speed remains constant without dropping when the clutch is engaged. Are you referring to the pilot bearing as the needle bearing on the crankshaft, near the transmission?
- All mass connections and power supplies to the MSG are low impedance (less than 0.2 Ohms) within the resolution of the DMM.
Sure, here's the translation:

"Best regards," or "Sincerely," (depending on the context).
Herbert.

Hi there,
At the very least, to understand the mysterious value for the read-out supply voltage, I will next...
- Inspect the main power cables and 12V lines leading to the MSG individually under load (using a test lamp).
- Check the target battery voltage at the connectors for:
Mass airflow sensor (Contact #7); Turbocharger boost control valve (N75) (#2), fuel injection timing control unit (N108) (#3), exhaust gas recirculation system (N18) (#2); mass air flow meter (#3).

Does the fuel shut-off valve require battery voltage to function?

Ideally, a test box would be installed between the main system gateway (MSG) and the connector.
hg
Herbert.

Hi there,
Last weekend, I did some more thorough searching.
It was quite noticeable that the supply voltage value in module MWB 12 kept changing. Perhaps I should have been more explicit and said that the value jumped from one "ignition" event to the next.
In any case, the same was observed when measuring the voltage at terminal 15. Therefore, the ignition switch was the likely culprit. After replacing it, the voltage at terminal 15 remains constant, as does the voltage output from the MSG (Main Control Unit) in module 12.
The latter remains consistently low, at 10.5V when the ignition is turned on and approximately 11.8V with the engine running (whereas it measures 12.5V or 14.2V directly at the battery).
Next, the voltage at the MSG connector was measured under load. I used a 55W H3 lamp as the load, which draws approximately 4.5A, corresponding to the current draw of the MSG. With this setup, I measured 11.5V across all possible 12V/ground wire combinations at the MSG connector, with 12V present at terminal 15 or 30 relative to the ground point for the MSG wiring harness.
The "lost" 0.5 V are distributed across further measurements, with portions appearing on the ground connection to the MSG connector (0.2 V) and on the 12V connection (0.27 V).
The ground connection consists of, in addition to the wire, a crimped branch in the MSG cable harness, the crimped contact in the MSG connector, and during testing, the contact between the MSG terminal and the test probe instead of the MSG connector's contact. The 12V connection also included the connector contacts between the relay holder and J249 (where I made the connection).
Given the age of the vehicle, I consider the voltage drop and corresponding connection resistance to be normal. What is missing is an explanation for the difference between the voltage measured at the connector and the voltage value reported by the MSG (Main System Gateway). I suspect aging effects (components, solder joints).
Sure, here's the translation:

"Best regards," or "Sincerely," (depending on the context).
Herbert.

Herbert wrote:

What is missing is an explanation for the difference between the voltage at the plug and the voltage value reported by the MSG. I suspect aging effects (components, solder joints).

Moreover, the MSG is not a remotely accurate voltmeter.
Regarding the EDC15, the conversion parameters between the ADC and the diagnostic format seem more like a rough guess than a carefully calculated value, and the software is not even individually adjusted to the hardware tolerances of the ADC – and I don't think that's different with the MSA12.
So, you're essentially comparing your measuring device (what tolerances does it even have?) to the rudimentary estimation feature of a Bosch engine control unit. In approximately one case out of every thousand years, you might get identical readings.
If you have time, please check the maintenance workbooks (MWB) of all your stations (StGe) for the onboard voltage, and be amazed by the discrepancies between the values that each station "measures" .

Has the problem (the engine cutting out) been fixed with the new ignition switch?

Quote:

Is the problem (engine stalling) with the new ignition switch fixed?

As mentioned earlier, the engine stalled twice in quick succession, and the cause is unknown. Replacing the ignition switch may have only addressed a secondary issue.
It is already clear that a 20-year-old MSA 12 MSG does not provide 0.1 V measurement accuracy. However, based on the design and EOL component tolerances, it should at least be such that the input/output function works for the J249 and the glow plug heater. Further discussion about measurement accuracy is pointless.
Sure, here's the translation:

"Best regards," or "Sincerely," (depending on the context).
Herbert.

Thank you for the feedback!

The engine still runs with a battery voltage of only 10 volts. At least, that's what the EDC15 indicates; it needs a minimum of 7V to function. It's also unlikely to be the clutch switch, especially in TDI models, because when shifting gears without depressing the clutch, the engine has enough inertia to keep running even without any "warning." You might expect a drop of about 50 rpm in this case.

(Both tested)

Can you definitively verify a complete disengagement of the clutch? Otherwise, the ignition switch explains it quite well: when the engine control unit (ECU) loses power from the ignition circuit, the engine shuts off and only restarts when the power returns. However, I'm puzzled as to why this happened while you were releasing the clutch. Were both hands on the steering wheel at that time? Perhaps you moved or jolted the steering column more than usual when extending your leg.

Sure, here is the translation of the text from German to English:

"Hello."

The clutch is working properly; otherwise, it would manifest itself differently. I already mentioned something about the ignition switch above.
Let's close this thread for now with your gratefully accepted comments. I will post again if new information becomes available.
Sure, here's the translation:

"Best regards," or "Sincerely," (depending on the context).
Herbert.