Occasional starting problems with the Lupo 1.4 TDI (Solution)

Good day.

I've been having a problem with my small, 3-cylinder engine for some time now.

Sure, here's the translation:

"Here's the following procedure:"

Normally, it starts immediately when you turn the key, and this only takes a fraction of a second. So, everything is as it should be.

However, if I want to turn it off and restart it, I can let it idle for as long as the battery allows, and absolutely nothing happens. However, it doesn't smell like diesel, and there's no smoke or anything of the sort coming from the exhaust.

And then, after several attempts (with the ignition completely off), it starts immediately and without hesitation, as if nothing had happened.

And when it runs, it runs smoothly, without any jerks or glitches. He fully commits and shows no signs of wanting to do anything other than what he's supposed to do.

The fuel pump is running as usual when the ignition is turned on. The starter motor is relatively new. The battery is fully charged (3 years old, and has been used for a lot of long-distance driving). Fuel is always purchased at the same gas station, and always until the pump automatically shuts off.

The only irregularity I've noticed is that the preheating indicator light sometimes doesn't illuminate when the ignition is turned on. As far as I know, it should always light up briefly, right? Otherwise, I can't detect any irregularities, nor can I identify any pattern in the occurrence of this problem.

My ideas would be:

- Relay 109
- Fuel filter
- "Toad" on the filter.


Does anyone else experience this problem?
The various websites I consulted were not helpful, as the symptoms described there were different.

Hi,

If the indicator light is not illuminated, the MSTG is not receiving power: Replace relay 109.

Alternatively, you can tap on the relay to test it if it doesn't want to start.

Regards,
Adrian.

But that only happens sometimes... I'm going to the store now to get one.
Alternatively, I've read in this forum that this could also be due to the Hall sensor (+connector/contacts).

Hi,

Yes, sometimes it may not be able to establish a connection. Or, it could be that the relay is "stuck," in which case the situation is reversed: the key is removed, but the engine continues to run because the relay is not releasing.
The new relay is a small investment...
Regards,
Adrian.

LupoTDI wrote:

But that only happens sometimes... I'm going to the store now to get one. Alternatively, I read here in the forum that this could also be due to the Hall sensor (+connector/contacts)?

If the sensors are defective, the engine control unit usually stores corresponding error codes, which can be read out using VCDS.

Unfortunately, I won't be able to read that until the end of the week. Is it also common for the starter motor to sometimes start and sometimes not when using a jump starter?

Okay, I'll pick it up now and then I'll take a look.
The question is whether it's normal for the engine to run perfectly even when it's defective. Because, ultimately, it's really just these startup problems.

I'm just throwing this out there... the ZAS.

Good evening.

Thank you again for all the helpful tips you provided.

Yesterday, I replaced relay 109, and since then I've been trying everything I can to trigger the problem. I've really tried everything, but it seems the problem was actually caused by the relay. I opened it, but it looks perfectly fine...

Well. I hope that was the issue, otherwise I will get back to you and explore other options.

Best regards,

Hi,

Thank you for the feedback.
You don't just look at electrical components; you measure them.

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Regards,
Adrian.

I completely agree with you!


How do I measure a relay that occasionally has problems?

Hello everyone!

LupoTDI wrote:

... Only how do I measure a relay that is having sporadic problems?

Simply put: By measuring the voltages using a multimeter in the original, built-in state, and then identifying the faulty relay based on those measurements.
Of course, using VCDS would make it faster, more convenient, and more comprehensive, but that's okay.

The detached solder joints are often only visible under a magnifying glass and, of course, can only be recognized with experience.

Best regards from Munich!