1.9 TDI PD engine starts increasingly poorly

Hello,
Here's the translation:

"This is about the following vehicle:"
VW Bora.
1.9 TDI engine, code: ASZ, 131 horsepower.
Mileage: 270,000 km
Year of construction: 09/2001.

The car starts poorly regardless of the temperature. Sometimes it starts after about 5-7 seconds of cranking.
Sometimes it doesn't start at all, while the tachometer randomly jumps from 0 to 4000 rpm. Only turning the ignition off and on again, and then trying to start it again, will eventually get the car running. Afterward, the dashboard displays "Engine fault, workshop" and the glow plug indicator blinks. The error memory then always contains the following error code: "16989 - Control unit defective P0605 - 35-10 - ROM error - Intermittent".As soon as the vehicle is subjected to a higher engine speed (2500-3000 rpm), the blinking filament disappears.

VCDS is available.

Already checked / replaced:

- Diesel filter replaced, including the return valve (also known as a "Knackfrosch").
- Tandem pump checked (approximately 7 bar at 1500 rpm).
- MWB 13 data read and analyzed (target vs. actual values compared, all within the tolerance range. A log will be created and posted if necessary).
- Clear hose after the diesel filter (no air bubbles when the engine is running, only a few tiny air bubbles when starting).
- Starter motor and battery are approximately 2 years old.
- Timing belt replaced a week ago (due for replacement).
- Coolant temperature sensor replaced.
- The contact points on the battery and the transmission were cleaned and treated with terminal grease.
- The positive contact on the starter motor was cleaned and treated with contact grease.
- Checked the wiring harness from the starter motor to the fuel injector rail (on the left side of the engine) for any signs of abrasion.
- Fuel pump activated via VCDS. While "activation" is blinking, the glow plug indicator flashes in the instrument cluster, and the display shows "Engine fault - workshop". (No confirmation whether this is the correct behavior.)
- Edit: Also renewed were relay 109, as well as the fuel pump relay.

Unfortunately, the vehicle is still starting poorly.

Thank you in advance for any helpful contributions!

Sincerely,

Hello,

What voltage does the engine control unit (ECU) see when the ignition is on but the engine is off? Please refer to the measurement block for details.
What engine speed is reached during the (failed) start? Log the engine speed during startup.
What coolant temperature does the engine control unit (measuring block...) see, and is this value plausible?

Best regards, Rainer.

The battery voltage, with the ignition on and the engine off, is 12.31V at the control unit.
According to the log, the motor speed is constantly at 2961 rpm.
The coolant temperature seems reasonable; it was 45 degrees 30 minutes after I turned the engine off.


Best regards.

The engine speed reading is likely incorrect. During the starting attempt, the maximum speed that can be reached is probably >600 RPM, if anything at all. You mentioned that your tachometer is also exhibiting strange behavior...

I'd like to start investigating this. Was the error already present before the fuel pump replacement? (I assume from your post: yes). Are there any cables in the area of the sensors (or their ends at the control module) that are damaged or bent? This applies to the crankshaft and camshaft sensors.

hoi.hoi wrote:

The error memory always contains the following error: "16989 - Control unit defective P0605 - 35-10 - ROM error - Intermittent".

Before I tear apart the engine wiring harness and replace half of the peripheral hardware, my immediate goal (due to the rather specific error entry) would be to test a different MSG (Modular Service Gateway).

Today, I created a log file.
Overall, I logged 3 attempts to start, but only the third one was successful.
I have a relatively similar engine control unit (ECU) from another Bora with the ASZ engine available. However, would the WFS need to be reprogrammed?

The immobilizer needs to be reprogrammed. To do this, you need the vehicle-specific PIN code.

If it's only about starting the engine, you can leave the WFS (Warm-up Fuel System) disconnected.
The engine just turns off after a second.

Wiesel wrote:

If it's only about starting the engine, you can leave the WFS out. Der Motor geht halt nach einer Sekunde wieder aus.

Hello!

Tomorrow, I will install the aforementioned MSG and see what happens.
Can the donor MSG (Main System Module) simply be reinstalled into the donor Bora if the only thing that was done to it was to test its functionality by starting the problem vehicle?

Best regards.

Yes, as long as you don't change anything about the MSG. You can also test your own MSG on the donor Bora.
hg
Herbert.

Hello,
Replacing the engine control unit didn't improve the situation; the vehicle still starts poorly.
Before replacing the MSG (Modular Servo Gear), the fault memory was read again. The following errors were stored:

2 error codes found:

16989 - Control unit defective.
P0605 - 35-00 - ROM Error.
16705 - Motor speed sensor (G28)
P0321 - 35-00 - Implausible signal.

After the unsuccessful swap, the engine speed sensor was removed and cleaned. Unfortunately, this did not resolve the issue.

Best regards.

2001 Bora - isn't it similar to the Golf 4?

Look, see if there's a fuse box directly on the battery that's just corroding away.

Hello, yes, the vehicles are largely identical to each other. I had the fuse box open recently and was looking for any defective or corroded fuses.

Best regards.

I would like to check the on-board voltage during the starting process using an oscilloscope.
The diagnostic information during the startup process (log) is relevant to the Lokus. What function does "Relay 109" perform?

Relay 109, as far as I know, controls the power supply for the MSG, among other things. I can create another log if I know what specific information needs to be logged and how.

Best regards.

Quote:

Nach dem erfolglosen Tausch, wurde der Motordrehzahlgeber ausgebaut und gereinigt. Leider brachte auch dies keine Änderung der Problematik.

If I'm interpreting your last log correctly, the speed signal is either completely missing or is implausible. The control unit (STG) can be ruled out.

Then, the remaining possibilities are the crankshaft position sensor, the wiring harness, and/or the power supply to the engine control unit.

Personally, I would suggest adding a few auxiliary wires from the STG (Steuergerät - control unit) to the speed sensor.
First of all, I would replace the very old speed sensor, regardless of whether it is defective or not.