Passat TDI Starting Problems: Troubleshooting Guide

Hello fellow mechanics.

Hatte heute morgen grosse Probleme, meinen TDI bei -13 Grad anzuschmeissen. Vorglühzeit war 5 Sekunden und danach musste ich 3 Sekunden orgeln, bis der Motor angesprungen ist. Aus dem Auspuff hat sich eine grosse blau-schwarze Wolke verabschiedet und in den ersten 10 Sekunden war der Leerlauf unregelmässig. Nach 100 Meter wollte ich dezent Gas geben, aber der Motor hatte zwischen 2000 und 2500 Umdrehungen pro Minute extreme Ruckler. Im Leerlauf konnte ich den Motor problemlos von 2000 bis 3000 Umdrehungen pro Minute hochdrehen. Als es dann leicht bergauf ging, hoppelte der Passat wie ein Känguruh ab 2000 Umdrehungen pro Minute. Als die Kühlwassertemperatur den Kaltbereich verlassen hat, war wieder alles normal. Ich habe den Passat laufen lassen und gleich das LAptop mit VAG-Com angehängt und den Fehlerspeicher ausgelesen und verschiedene Messwertblöcke überprüft. Keine Fehler im System und auch die anderen Werte lagen im grünen Bereich. Daraufhin habe ich in der Werkstatt mal den Dieselfilter entwässert und warte jetzt auf den nächsten kalten Morgen, um das Startverhalten erneut zu testen. KaCould it be that at these sub-zero temperatures, the diesel becomes thick, which can cause these problems?

Winter greetings.

hb2000

Hello,

Okay, so if you have the correct winter diesel in your tank, it shouldn't be possible for this to happen at -13 degrees Celsius. However, my engine also stalled yesterday. My colleague's engine did too. We probably both got bad diesel from the same gas station .

Best regards, Christian.

@hb2000:

This could also indicate a very high compression ratio and/or leaks in the fuel supply system.
At these low temperatures, the viscosity increases extremely. Consequently, the pressure loss across the differential pressure sensor increases significantly, meaning that even a small leak in the fuel line may only become apparent under these extreme conditions.
And if the pump cannot build up sufficient internal pressure, then the injection timing control will not function properly.

Regards,
Alex.

Best regards.

I should actually have winter diesel in my tank, as it has been available at the gas station since October, and I always fill up at the same station.
Perhaps draining the diesel filter helped, as a small amount of water (5ml) came out before diesel started flowing from the filter.

Regards,

hb2000

It sounds more like one or more spark plugs have failed, and your engine isn't reaching the required ignition temperature in one cylinder!

However, the glow plugs switch off again after a few hundred meters - The engine was still misfiring until I left the cold area, which was likely due to the coolant. Of course, the glow plugs might not be in the best condition either, given the car has 160,000 kilometers. I think it was probably water in the diesel fuel, as the fuel filter has already been replaced 60,000 kilometers ago.

"Okay, so far it's consumed 5ml of water in 60,000 km, and otherwise it's been running on pure diesel. Go ahead and replace the fuel filter (you can find them for about 1/3 of the price at a well-stocked auto parts store compared to VW). Then, turn the filter upside down and let everything drain into a safe container for disposal. Let me know what you find. We've discussed this before, and I did this after about 30,000 km because I often refuel at less reputable gas stations. I found all sorts of things in there. Since then, I've also installed a regular fuel pre-filter, as mentioned in a technical article about extending the fuel filter's service interval."

Okay, so if you let the stuff that comes out of the filter sit for about an hour, and the container is transparent, then you can (at least I could) clearly see the separation layer, so there was quite a bit of water in it.

It probably wouldn't run for too long. You could also prepare to replace the glow plugs during that process. Maybe test the glow plugs first, but I think there's likely to be a faulty one.
"In my ASZ engine, everything is still in good condition at 46,000 km. In our ALH engine, two glow plugs were defective at around 60,000 km."

matthiasTDI96 wrote:

Maybe we should test the candles first... In my ASZ engine, everything is still in good condition at 46,000 km. In our ALH engine, two injectors were defective at approximately 60,000 km.

I can definitely understand why.
Our ALH-Ibiza engine roughly takes about 5 times longer to reach operating temperature compared to the AFN or ASZ engines.

For that, in the spring, the glow plug fuse regularly breaks , and at the beginning of winter, I have to repair it...

I remember you saying that before, Ulf... I think we might have a similar issue here in the spring.

I don't have an AFN at all - It's the good old AJM with all its quirks...

Yes, but your AJM is old enough to get new spark plugs.

Do you think I should buy my colleague some new spark plugs...

And the glow plug heater for the coolant is probably also going to need to be replaced...

And somehow, I also suspect the thermostat, that it's opening the cooling circuit much too early, because the car isn't getting properly warm at all.
And of course, there are still a few more parts that could be replaced, because 160,000 km is already half a car's lifespan, and it simply leaves its mark on the vehicle.

No, that's not what I meant.
First, check them, then replace them. But I'm just going to assume that one of the spark plugs is faulty.
You can also check the thermostat, but you would have to remove it, and I'm not sure if it's worth it. However, I can reassure you that in my car, it doesn't produce much heat below 0°C anyway. That's why I have a supplemental heater.

This morning, I had a lot of trouble starting my TDI in -13 degrees Celsius. The preheating time was 5 seconds, and then I had to crank the engine for 3 seconds before it started. A large blue-black cloud came out of the exhaust, and the idle was irregular for the first 10 seconds.


My Audi AHF, manufactured in 1998 and with 165,000 km on the odometer, exhibited the exact same behavior at -10 degrees Celsius. A test of the glow plugs is recommended.
It showed that 3 out of 4 were defective.

Revving a cold engine to 3000 RPM in -13 degree Celsius temperatures would be something I wouldn't do.
a bit too risky.