AVF TDI engine in Passat starts strangely when cold sometimes!?

Hello!
"Our 96kw AVF TDI sometimes starts strangely. The following happens: You turn the key, and the starter motor begins to turn. In 98% of cases, it starts immediately, in a typical PD fashion (it even starts running as soon as you turn the key)." Sometimes, he just behaves differently, and it's like this:
a) The starter motor spins for a slightly longer time than usual, but the engine then starts. I have the impression that it rotates slightly slower in this case .
b) The starter motor turns the engine one revolution and then seems to get stuck (the engine can still be heard stopping). Then there's another strong jolt, and it starts running.

a) and b) always only in the cold state! When warm or with the auxiliary heating on, it always starts quickly and immediately, until today. Today, after preheating, there was a case that had never happened before. It starts and immediately turns off when you turn the key back! Attention, do not confuse this with the WFS! That was NOT the WFS!

Does anyone have any ideas what might be going on? Sure, I can help with that. Please provide the text you would like me to translate from German to English.
No errors in memory.
4 new spark plugs.
PD elements according to. Idle speed control is OK.
LMM values are completely fine.
Valve timings are also okay.
Battery OK.
Performance and consumption are, in my opinion, okay.
No stuttering or any other issues after starting the engine or while driving. Completely stable idle.

My suspicion is the starter motor, especially considering case b). It can't be that the starter motor stops briefly even when in the start position! What worries me, however, is what happened today. I preheated the engine with SH, released the key because the system indicated "running," and then it immediately shut off again. After that, I immediately restarted it, and it started right up.

Do you have any suggestions as to what might be causing this and what else I could try? Okay, it's not something that happens often, but it's annoying to know that something isn't 100% okay.

Thank you.

Greetings.

Quote:

Battery OK

Sure , or could she possibly have cell damage?

Before continuing the search, the error should be ruled out.

It sounds like one cylinder is firing and working against the starter motor...

I would have guessed it was the battery too. Check the cold start performance!
In order to truly rule that out. Because starter batteries often fail prematurely when used to power auxiliary heaters, as they are not designed for frequent charging and discharging.

Hello everyone!
Regarding the battery: People, this one is new from last year (an original factory battery for almost 180,- ), so I assume it's okay . And it almost always starts the car normally. Even at -12°C, it starts normally without any problems. Then, there's a start cycle again where it doesn't work 100% and it's like what's described above. How can they be objectively tested?

To ignite: what does that mean?

Greetings.

Mike3BG wrote:

After the preheating, there was a situation that had never occurred before. It starts up and immediately shuts off again when you turn the key back! Be careful not to confuse this with the WFS! That was NOT the WFS! Does anyone have any ideas what might be going on?

Spontaneously discharged: a gradually dissolving contact set in the ignition switch (voltage drops on terminal 15).

It sounds like one cylinder is firing and turning against the starter...

Then the injection would have to occur before top dead center (TDC), which, to my knowledge, doesn't happen in idle or under light load.

You absolutely cannot inject fuel directly into a PD (Pump Duse) injector. You can only inject fuel in the wrong direction with a common-rail system. However, you will clearly hear this, as the ZMS (if installed) will engage.

Best regards, Jochen.

@Ulf
Would it not also be possible that the engine could stall during the journey? It has never happened before! Okay, I have 2 radios connected to the original (ISO) wiring (using a Y-adapter). But does that not make a difference? So far, I haven't had any problems with it!
Is there a way to check the voltages? Okay, what should I measure with VAG-Com *before* a cold start?

Greetings.

It's probably the ignition switch. There are two contacts there. One of them, which sends power to the starter when you turn the key too far, might be broken. Contact pressure (for your radio, for example, it's different).

and a problem with the "ignition switch" can then only occur when starting the engine and only occasionally?

Greetings.

Quote:

And so, a problem with the "ignition switch" could then only occur when starting the engine, and only occasionally? icon_rolleyes.gif

I don't think that's the case here, because the starter motor isn't disengaging after starting, which is what it would do if it was intermittently not receiving power.
Possible causes could include a poor ground connection to the engine, a faulty positive connection (terminal 30) to the starter, or a defective starter solenoid.

However, to be 100% sure, I would suggest trying a different battery as a test.

Hi,

"There has never been any issue when the engine is warm. So, if the engine was warmed up by its own power and not just by the auxiliary heater. There were also no issues in the summer, not even during cold starts. Of course, it could be a coincidence, but I believe it only happens when it's colder outside, like now, and during cold starts. Until yesterday, I also thought that the auxiliary heater was masking this "flaw." But that's no longer the case, as you can see from case b) above. Also, there has never been an issue when I start the engine cold, drive for 50 meters, and then turn it off to restart it 2 minutes later (cold start). There has never been anything in those situations either." Based on my feeling, it's like a) the starter motor sometimes struggles, and once, as I said, it almost got stuck, like when the battery fails. I'm not sure what to make of it. All I know is that the starter motor has been removed three times in total, for clutch replacements, but it's never caused any problems until now. Now, it's acting up during cold starts. Even though it's only happening very rarely, it's annoying. Also, it has never stalled after starting (case b). It starts quickly and immediately turns off when you release the key. No error codes. Damn. What do you think about the crankshaft position sensor? Could a faulty speed sensor cause this kind of behavior?

Regarding the magnetic switch: Is it available as a separate component? Where is it located? Everything that stays within the specified parameters, I can exchange, but I can only exchange the starter or the ignition switch for testing purposes .

Greetings.

Quote:

Regarding the recessed magnetic switch: is it available individually? Where is it located? Everything that stays within the warranty can be exchanged, but I can only swap the starter or the ignition switch for testing purposes.

It's best to start with the simplest things to narrow down the source of the error.

...and what would that be? How should I proceed systematically? I do have VAG-COM, but it won't be compatible with that .

Greetings.

"In cold weather, the starter motor requires more power, and therefore more current. It's important to check the battery and electrical connections. I'm not sure if you can see a voltage drop using VAG-COM (worth trying). Ideally, a free load test at a place like ATU would be a good idea (definitely get it checked). However, a battery that occasionally weakens can be difficult to detect this way. Otherwise, connect a multimeter to the battery or starter motor before each cold start. One must be able to recognize irregularities.

Mike3BG wrote:

It has never completely shut down after starting (case b). It starts quickly, but immediately turns off when you release the key. There are no error codes stored. Damn.

I still maintain that this perfectly explains the voltage drop at terminal 15 caused by the ignition switch being turned back.
The MSG interprets this as a normal stop command and therefore does not report an error.

If the problem with the ignition switch continues to develop, you will soon be able to observe this phenomenon more frequently.