Glow plug current draw?

sidepod · Feb 25, 2024

Any one out there actually measured the load on the glow plugs?

I’m fairly confident I’ve at least one dead plug.
Obvs the simple test is to measure the resistance but it’s a nightmare to get to the plugs. At this stage I’m just investigating.

With a clamp meter on the feed from the relay I’m seeing around 45A so by my maths, I have at least one dead plug.

Anyone taken similar measurements?

welshwestie · Feb 28, 2024

Glühkerze – T4-Wiki

t4-wiki.de

T4wiki article states 8 - 10a per plug. So 5x 8/10 is 40a to 50a.

I guess you have read this https://t4-wiki.de/wiki/Glühkerzen_(Prüfen)

sidepod · Feb 28, 2024

welshwestie said:
Glühkerze – T4-Wiki

t4-wiki.de

T4wiki article states 8 - 10a per plug. So 5x 8/10 is 40a to 50a.

I guess you have read this https://t4-wiki.de/wiki/Glühkerzen_(Prüfen)

I’ve not looked at that. Read pretty much every other glow plug thread online!

Resistance is 1ohm so simple Ohms law says 12A per plug, 60A total.

Watching the clamp meter with the engine running I can see the load settles around 36A and decreases. Resistance increasing with temp, current falling. I’ve not monitored it through the full 3 minute post start cycle.

Once I get time I’ll see if I can get and accurate resistance reading on each plug and check the wiring.

sidepod · Feb 28, 2024

That’s a good read, once translated.

I think it does confirm I have at least one dead plug. Although it warns against checking the load pre-start due to high current draw, that was when I was seeing 45A. So, even if the good plugs were drawing high initial current, there still isn’t enough for 5 good plugs.

To be continued……

sidepod · Feb 28, 2024

Well everyday is a school day!

Just reading through the pre/post annealing section, I discovered that the glow plug sequence actually starts with drivers door switch operation.
Never knew that, I always assumed it was with ignition.

WelshGas · Feb 28, 2024

sidepod said:
Well everyday is a school day!

Just reading through the pre/post annealing section, I discovered that the glow plug sequence actually starts with drivers door switch operation.
Never knew that, I always assumed it was with ignition.

Is that switching On and checking the circuit or actually powering the circuit and heating glow plugs?

sidepod · Feb 28, 2024

The actual glow process or “pre-glow “

The pre-glowing process is already initiated when the driver's door is opened, for which the corresponding door contact switch (TKoL) is monitored. A pre-glow via the ignition it switch is of course also possible, or is the only way to pre-glow under certain circumstances. The following logic applies to the annealing process:

At a coolant temperature > 65°C, there is no pre-annealed.
The pre-glowing is started with the opening of the driver's door. However, the pre-glow indicator only lights up after the ignition is switched on and therefore only shows the remaining glow time.
After a double glow activation via the door contact switch, the pre-glow is blocked via the driver's door. The annealing process can then only be initiated with the ignition key. The lock is lifted after the engine start if the coolant temperature exceeds 65°C and the ignition is switched off.
After the engine has started, the post-glowing time begins, which can be a maximum of 3 minutes. It ends when the coolant temperature exceeds 65°C.

sidepod · Mar 2, 2024

Update on this.

Background. Van has been getting tricky to light from cold. Once lit it stumbles and runs on 3 or 4 pots for around 10 seconds then clears its throat and all is good. Plenty of embarrassing white smoke from the rear. Once up and away, all is as it should be. Restarts when warm are perfect.

I’ve checked all sensors etc and I was convinced it was glow plugs.

Chatting to my local indie, I’d not finished explaining before he interrupted me. Cracked tank sender unit. They’re prone to hairline cracks which allows air into the fuel loop and causing the fuel to drain back to the tank.

Bosh. Done. The power of a good indie.