Glow plug indicator function

Hello!

I learned something new again.

Last week, when it was so cold, my work van, a T5, wouldn't start. It's supposed to be a PD engine, but without a turbo. This has been a problem for a while, as it's always been a bit rough to start in cold weather, but at -15°C, it just wouldn't turn over. I've long suspected that the glow plugs aren't working, but since I'm getting a new car soon anyway, I'm only doing the absolute essentials for now.
Okay, so that day I knew I wouldn't need the car, but I would the next day. I tried starting it first thing in the morning, but it wouldn't start. Since we have maintenance contracts and mobility guarantees for the cars, I called VW-Fritze. I told them that the car wouldn't start in the cold, the starter motor was turning normally, and I thought a few glow plugs might be broken.
The VW driver gets in, turns on the ignition, and tells me, "Yes, that's how it will be with the glow plugs; 'the preheating indicator light stays on for far too long.'"
I didn't really think much about it at first.
Around noon, the car returned, and it turned out that all four glow plugs were defective.

And the next day, it was just as cold, the preheating indicator only lit up for about 3 seconds instead of the previous ~10 seconds, and the car started immediately.

My private Golf (G4, ALH) had a similar issue; it would glow for about 8 seconds (according to the glow plug indicator in the dashboard), and while it would still start in the cold, it would barely start.

Since I had some time, I thought I'd also check the glow plugs. Three were defective. I installed new ones today, and sure enough, the preheating coil is only glowing for about 3 seconds. Of course, it started right up, given the current temperature of around 5°C.

Question:
Can someone explain how the glow plug relay works, or whether you can reliably identify faulty glow plugs based on the "displayed" glow time?
And how does it work electrically?

Look over there:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.
To my knowledge, the preheating time is also regulated based on the engine temperature in newer engines.
Faulty glow plugs shouldn't have any effect. The logic behind that would be strange.
hg
Herbert.

"...regarding the preheating time, it's clear that it's related to the engine temperature, but it's not clear why there's such a time difference of 7 seconds between working and faulty glow plugs, because in both cases, according to the information provided, the engine was cold..."

Greetings, Styrian.

Hi!

Yes, that's exactly what's strange and what I don't understand, which is why I'm asking the question.
But I did mention that there might be something to it.
especially after the mechanic's statement... and now also based on my own experience.

Well, unfortunately, I didn't even think to test that when I was changing my own spark plugs.
Perhaps there's someone here who has changed spark plugs in a car like this before, and paid attention to something specific.

Quote:

..das mit der Vorglühzeit ist insoweit mit der Motortemperatur klar, nur ist nicht klar, warum zwischen funktionierenden und defekten Glühkerzen so ein Zeitunterschied von 7 Sekunden entsteht, denn in beiden Fällen war ja - laut Aussage - der Motor kalt...

I can imagine it like this: With a functioning heating element, the resistance or current flow is measured. When the value X is reached, (the indicator light) is switched off.

If the initial values are incorrect (e.g., a faulty spark plug), the system may pre-ignite for a maximum time period, after which it will be shut down for safety reasons.

What's the point of that? The cylinders with the faulty spark plugs won't be pre-ignited anyway, and the other cylinders will fire regardless.
hg
Herbert.

Quote:

Was soll das für einen Sinn machen?

Okay, how do you think the question about shorter burning times (lamp extinguishes) with intact glow plugs and the same temperatures should be answered?

...also laut T4-Wiki gibt es eine Leitung vom Relais der Glühkerzen zum Vorglühsteuergerät J425. Diese wäre sinnfrei, wenn nicht das Steuergerät auch die Glühkerzen damit überprüfen bzw. die Stromaufnahme damit ermessen könnte. Wobei ich irgendwo auch zu gelesen haben glaube, dass das eigentliche Vorglühen mit dem Betätigen des Türkontaktes erfolgt und mit Zündung eigentlich nur die Nachglühzeit so lange fortgeführt wird, bis die Motortemp >65Ĉ ist. Wobei -> to be wrong is masculine.

Greetings, Styrian.

Hi!

As far as I know, the turbocharger contact issue only applies to ABL engines.

In the first post, the preheating times and temperatures aren't entirely comparable. 10 seconds at -10°C is normal, as is 3 seconds at +5°C.
And what's the point of linking it to the Turkish contact?
Please provide the URL of the T4 Wiki entry.
Das Relais der Glühkerzen hängt natürlich am Vorglühsteuergerät. Zum Input/Output switching.
hg
Herbert.

Hello everyone!

Bevor's hier noch zum Streiten wird...
Let's leave the post as it is for now.

I'm in contact with the person identified as "G.Punkt" regarding this PM motor, and it appears to be an AXC motor from 2006, although this needs to be confirmed more precisely in the coming days.

Just like HerBärt, I believe the theory that the preheating indicator light stays on longer in case of a fault is complete nonsense.
Regarding the T5 with AXC, it does not have a "pre-glow (time) control unit" or any other way of measuring current connected to the GSK - that is certain!! This applies throughout all production years...
The MStG (glow plug control unit) directly controls the glow plug relay, and the power circuit connects directly to the engine control units (ECUs) without any taps for potential feedback or measurement.
It makes even less sense to try to compensate for an error in the preheating system by extending the time, rather than recording the error in the VAT register.

The issue with the pre-glow function being activated via the driver's door likely doesn't relate to the vehicle's year of manufacture.

And finally: People, WHAT makes this forum different from MotorBlöd or similar sites???!!!
Absolutely correct!!! Having incomplete knowledge is definitely not just undesirable here, but it actually hinders the path to problem-solving .

Best regards from Munich!

THX.
I'll take a look at the CJCD circuit diagram.
Sure, here's the translation:

"Best regards."
Herbert.

Servus HerBärt!

Of course, it has a preheating control unit, often referred to as a "glow time automatic control unit," designated J179, where each glow plug can be individually powered, allowing for the measurement of current and resistance.

Best regards from Munich!

...regarding the link: http://www.t4-wiki.de/wiki/Vorgl%C3%BChanlage ...and we don't want to argue here, but rather share insights and correct any potential misunderstandings...

Greetings, Styrian.

Hello!

Okay everyone, thanks to the "Diesel Bear" (presumably a reference to a VW mascot or a humorous term), the situation has been clarified: It's not possible to perform an electricity consumption measurement on that car. Two different employees at the VW workshop told me the same thing, and because it sounded so convincing, I initially believed them.
I think they'll start believing it themselves soon.

"With my own Golf IV, that was nonsense because it was warmer than when I changed the spark plugs. I tried it myself today, with and without the temperature sensor, and with and without the glow plugs."

Regarding the company car, I swear on a stack of pancakes that it glowed noticeably less brightly the day after the glow plug replacement.

Are there any other possible explanations for the issue with the temperature sensor, or perhaps something else that was repaired without my knowledge? I don't see an invoice. There were no visible error messages for the driver. The car has always had very poor engine performance, with a maximum speed of 130 km/h. I drove it today, but I didn't think about or pay attention to whether it was running better.
I don't take my laptop to the company car either.

Thinking about it, the T5, compared to what we have now, always seemed to glow for a relatively long time, after the display.

Okay, regarding the T4 Wiki:

Quote:

Es wird immer nur bei Temperaturen unter 30°C geglüht und bei Erreichen der 30°C wird das Glühen sofort unterbrochen. Das Vorglühen wird allerdings erst bei einer Temperatur unter ca. 5 bis 10°C angezeigt.

The T4 Wiki is generally quite good, but this part is nonsense.
I don't read anything about Türkontakt.
hg
Herbert.