Glow plug firing duration

Hello everyone,

Since I also use biofuel to run my engine even in winter, especially on very cold days, it often starts reluctantly. Unless I pre-heat it, sometimes even up to 10 times, depending on the outside temperature. After that, it starts surprisingly well, although it doesn't respond to the accelerator quite as eagerly for the first 20-30 seconds, and then, after about 2-3 kilometers, it really starts to perform well.

I now have the following questions:
- When I turn on the ignition, the glow plug indicator light goes out after a certain time, but at the same moment, nothing is switched off (no click from any relay or increase in the fan speed). After a further period of time, a click can be heard from the area of the fuse box, and simultaneously, the fan speed increases (indicating a load shedding). Why does the indicator light turn off so much earlier?
- Is it possible to extend the preheating time, perhaps through the engine control unit? It would be great if we could avoid having to repeatedly turn the ignition key. There's also the option of installing additional electronics that would extend the preheating time. The software solution would, of course, be the more elegant one.

Hi,

The indicator only tells you how long the engine control unit (ECU) considers the preheating phase necessary for a safe start (using diesel). After that, there's a brief "standby heating" period if you don't react immediately, and then it turns off. After the initial ignition, there is a post-glow period lasting up to 4 minutes.

You can use an LED connected in parallel with the glow plug relay (usually relay 103) to observe its operation.

I would simply install two diodes and a switch in your place, using the switch to provide power to the pre-heating relay in a way that prevents damage to the MSG's outputs (that's why the diodes). Then you can glow for as long as you like, and do so without much effort.

Best regards,

Jan.

Hi! While I can't answer everything specifically, here are some facts I've observed about my AKU (agricultural machinery) and RME (biodiesel) in extremely cold weather:

- The heating time is temperature-dependent (EDIT: This has nothing to do with RME).
- When the temperature is below -10°C, preheating the device multiple times can be beneficial.
- Preheating more than 3 times does not provide any significant further improvement.
- Give it a little gas when starting, because the cold start fuel might not be enough for the first few seconds. EDIT: So, in my case, the engine stalled about 1 second after starting on one of the coldest mornings. On the next start, I immediately gave it full throttle and was able to keep up with him. (1400 RPM)
Theory 1: It's possible that the idle speed control is not yet active during the increased cold start fuel enrichment, and a drop below the low-limit (LL) speed does not increase the fuel injection amount beyond the cold start enrichment, unless the accelerator pedal is pressed.
Theory 2: In the region of low engine speed (LL), the compression end temperature was so low, the atomization and combustion were so poor, and there was an instability near the lower limit of LL speed, that even with the maximum fuel injection, the engine could not sustain operation. When you accelerate, you suppress the oscillation stabilizer.
-When starting the engine from cold, apply load immediately (i.e., start driving right away), shift gears early, and avoid high RPMs; this will allow the engine to reach operating temperature quickly.

Of course, this applies to a vehicle manufactured in 1998, and it certainly cannot be easily transferred to your car.

If things get really bad, you could try adding 10% Shell V-Power Diesel. It's supposed to ignite very easily. Mix it well, of course.

Regards,
Holger.

Hello,
RME also has a good cetane number, but its 'ignition temperature' is significantly higher than that of diesel.
It turns out that the preheating time for RME (biodiesel) is too short according to Volkswagen's specifications; it should be longer than for conventional diesel.
Best regards,
Günther.

Hi Gunther, yes, the ignition temperature of that V-Power stuff is supposed to be extremely low, and the cetane number is 58.

However, the cold viscosity of the fuel also plays a role, as it affects the quality of atomization. 'Extremely cold RME is quite tough.'

Given that, generally speaking, a fuel with a lower ignition temperature should also have a higher cetane number?

I would appreciate a well-reasoned explanation of the relationship between ignition temperature and cetane number.

Perhaps there are variables involved in the cetane number that are not relevant to the ignition temperature? For example, the ability to form highly reactive radicals under an atmosphere similar to that found in the combustion chamber of a diesel engine just before the start of injection?

Regards,
Holger.

Hello Holger,
The flash point of RME is 170 degrees Celsius, and the cetane number is 56-58.
I once read that RME (biodiesel) absorbs a significant amount of heat (latent heat of vaporization?) during atomization, but I can't remember where I saw that.
'Definitely, the RME requires a longer preheating time; therefore, my diesel engine starts poorly at 10 degrees Celsius compared to -10 degrees Celsius, even with three preheating cycles.' At 0 degrees, I cannot preheat.
Best regards,
Günther.

Hello!

'Where exactly can I find this dual-temperature sensor on a Volkswagen Golf 3 (1Z)?'
Can it also be tapped, for example, indoors, or only outdoors?
Control unit, i.e., inside the water tank?
(Would ideally also glow in the summer, in special cases.)

What exactly is the situation with the preheating relays?
(Mine actually has 4 wicks in the burning chambers.)
and 3 units for the coolant heater; 2 of them are connected in parallel.
Then there should be 3 relay coils, but so far I have...
'But I only found one, and it's located in the engine compartment.'
-> Do I also need to connect to that there?
(There are 4 x 20A flowing through it, it's that simple to just cut the wire, and...)
'It's probably not ideal if it keeps coming apart.'


Thank you for your responses!

Hello,
You can control this much more easily via the temperature sensor responsible for the preheating. This sensor is located in a plastic housing on the front left side of the engine, near the spark plug, in the G4 model, and is cooled by the coolant. You can now cut the connection wire and connect it to a switch inside the car. If the wire is disconnected, the engine control unit (ECU) receives a simulated temperature of -40°C, which allows for a maximum preheating time of approximately 20 seconds. I solved it by using an original taxi switch that fits into the center console of my G4.
Sure, here's the translation:

"Hello" or "Greetings"
Harald.

Hi.

Yes, I had a similar idea for a "Force Glow" button before.

I would interpret it as a button (or, electronically, as a timer). Because the temperature sensor doesn't just control the glow plugs; it also influences all the processes that the engine's electronic control unit regulates.
And if it's not -40 degrees Celsius, the TDI engine starts acting up and making all sorts of mistakes with things like fuel injection timing. And I would say that it shouldn't be operated for extended periods of time.

The button should ideally be located on the left side, as the right hand is usually on the steering wheel (and curious passengers won't be able to reach it).

m;

And where can I find the sensor on the G3?

I once read somewhere that you can change the preheating time in the engine control unit. I believe it was adaptation channel 12 (without guarantee).

[EDIT] /viewtopic.php?t=11122

@dieselmartin

There are several temperature sensors, and this one seems to be responsible only for the preheating process.
You can easily do it with a switch; there are no problems, even with longer preheating at higher temperatures. You can interrupt the preheating process by starting the engine whenever you want and then turn off the switch. But even if you keep the switch pressed and use the full afterglow time, there are no problems, based on my own experience.

@hollari
I don't know where the sensor is located on the G3. Simply test them all -> disconnect the plugs, turn on the ignition, and see which one keeps the glow plug light illuminated.

Sure, here's the translation:

"Hello" or "Greetings"
Harald.

@hharry:

I've already unplugged countless plugs, but...
It doesn't need to be preheated.


Could it be possible that the G3 uses an NTC sensor instead of a PTC sensor?
Does that mean I need to connect a resistor with a specific resistance value?