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Discussion Starter · #1 ·
When starting the car from cold, we all obviously turn the ignition on and wait for the glow plug light to go off before 'cranking' the engine.

When cranking the engine from cold does the power to your HU cut off for a short second (sound/display go dead) and then come back on again when the engine has started?

Does it only happen when the car has been standing for a good few hours?

Some feedback would be appreciated on this as i'm in the process of troubleshooting a minor problem.
 

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Quote: posted by Sem on 11/03/2005 22:28:11

When cranking the engine from cold does the power to your HU cut off for a short second (sound/display go dead) and then come back on again when the engine has started?

If I switch on the HU before I turn on the ignition, the HU turns off as the ignition fires and then switches back on again, but generally speaking, I don't put the HU on before I start the car.
 

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Discussion Starter · #6 ·
Quote: posted by golfv64mo on 11/03/2005 22:52:26

Quote: posted by Sem on 11/03/2005 22:28:11

When cranking the engine from cold does the power to your HU cut off for a short second (sound/display go dead) and then come back on again when the engine has started?

If I switch on the HU before I turn on the ignition, the HU turns off as the ignition fires and then switches back on again, but generally speaking, I don't put the HU on before I start the car.

Yeah, that's exactly what I mean!
 

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Discussion Starter · #7 ·
Quote: posted by Reflex TDI on 11/03/2005 22:55:24

Agree with you it goes off for a second.

But I never have the glowplug light, ever.

Maybe I was imagining it [B)] ....what I meant to say was I always wait until all lights go out before starting the engine.
 

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Quote: posted by Sem on 11/03/2005 22:57:20

Quote: posted by golfv64mo on 11/03/2005 22:52:26

If I switch on the HU before I turn on the ignition, the HU turns off as the ignition fires and then switches back on again, but generally speaking, I don't put the HU on before I start the car.

Yeah, that's exactly what I mean!

As far as I understand it, this is something built into most modern cars, as the ignition motor requires as much electrical power as possible to turn over the engine, and as such when the ignition is turned there is a 'surge' of power to the igition motor, which causes your HU to go off, and your lights to dim.

At least, that's as far as I understand it, and I might well be wrong - but it happens to me, and it was the same in the V6, so I'm pretty sure it's normal. [:)]
 

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Discussion Starter · #9 ·
Cheers for confirming, it's causing me a few headaches with my Phatnoise setup.....

1) Turn ignition > Phatbox starts booting

2) Wait for lights to go out > Crank engine

3) The Phatbox at this point has not completed the boot process and the power interuption causes it to crash occasionally.

I don't want to turn this into another 'Phatnoise' discussion though, we already have a 6 page thread in the ICE forum. This was just a general MK4 question [;)].
 

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Yeah mine does it but only usually when it has been standing overnight. I presume their is some sort of voltage sensor to the battery that cuts the power to the HU and other ancillires [sp!] so there is enough power to crank the engine.
 

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Quote: posted by Reflex TDI on 11/03/2005 22:55:24

Agree with you it goes off for a second.

But I never have the glowplug light, ever.

odd, my pd130 when putting ignition on always gives a quick show but only for a split second.
 

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Its Normal the HU fan and other major sources of power either stop all together or lower there load until you realease the key from maximum on the ignition.
 

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Had this on both Golf and Bora - tdi and petrol. The Volvo S40 Tdi does it too, as per Vwwwwing I have always beleived this to be a surge prevention thing, as my volvo headlights go off and back on when starting.

Glow plug light should only be on a sec or two until temp drops below -2C IMO.
 

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In the manual the glowplug heating is only in very low temperatures (< -15 DegC IIRC) so you can turn on the engine straight away. Re-assuring mind to watch the glow plug light come on for a second before starting.....
 

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Checked the battery water levels as I checked mine and it was quite low..............topped up and the battery comes across now as being more powerful. More noticable on cold mornings, as it used to take slightly longer to turn over (1-2 sec longer when freezing)
 

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There is a fault on some VW (diesel & petrol) attached to power up relay 109. I don't know if the PD cars have a similar system to my 110. Prior to replacing said relay, if the glow light didNOT come on, the car would crank and not start. (Generally in temps under 10centigrade.) This was a very intermittant fault and the car wouldn't start twice in 30k miles - the first time on the rollers at AmD![:I]

That said, my glow light generally comes on every time you start the car. The ancillaries are interrupted as some kind of surge protection I believe. Also to allow max power to the battery for start up.
 

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For the uninformed, of which there hopefully isn't many of you, of those that don't hope this helps..

When the glow light goes out it indicates that the glow plugs in each cylinder have reached a suitable temperature to cause the diezel to burn when under compression.

A warm/ hot engine does not require this assistance as the block temperature is high enough to do the job, and so the glow light will go out very quickly.

If you don't wait for the glow light to go out then all your doing is flooding the cylinders with diesel, which will eventually burn and start as diesel burns due to compression, but you risk damaging the glowplugs and pushing unburnt fuel into the exhaust.

On a side note,on older vehicles the glow light takes longer to go out as the glowplug is just an electrode that gets very hot, as they age they tend to take longer to warm up, either due to a build up of carbon or the electorde erroding/burning away.

As for turning the HU off, all vw's tend to do this due to the huge current drain on the battery whilst starting. Nearly all of the electrics of the car don't work whilst starting either. Try it!! Lights go off, wipers stop, elelcy windows don't move etc....
 

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Yep it caused by the X relief relay, it stops your wipers, fan and radio plus some other stuff. It's so the starter motor can have full voltage when turning over.
 
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