Voltage to glow plugs

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Darius

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Hello,
I have Audi a3 2007 1.9 tdi bls engine and i recently tried to mess around with my glow plugs trying to test something and I think I burned 3/4 of them (infinity ohms. no continuity. I assumed glow plugs receive 12v from the harness, so I removed the harness and connected them directly to the battery one by one for like 5-6secs. There was some sparks at first and then they went silent. So after that I looked at glow plugs and saw they are rated for 5v o.o (bosch duratem)
So what went wrong and how does it work? Can anyone shortly explain please? Do they receive 12v from the harness and I just connected them to battery for too long ?Or somewhere along the line (at glow plug relay or somewher else) the voltage gets lowered to 5v or lower and I connected them too way too high voltage and hence they dead?

Thanks in advance
 
The glow plug nominal voltage is around 4.4V not like traditional glow plugs which are 12V . There is an electronic controller that applies 12V initially for a fraction of a second and then drops this down by altering the duty cycle of the applied 12V using Pulse Width Modulation to control the temperature.
This results in very fast warm up of the plugs but if you connect them to a 12V supply they will burn out in a second or two. Good job they are not a silly price. Look for Beru or NGK items.
 
Sounds like they are toast now. Have a good close look at the loom as well they are prone to faults.
What is the problem your trying to cure?
 
Thanks for the replies guys! yeah by the looks of it I toasted them real good, that's a learning experience. I am trying to cure cold start issues. Once the ambient temperature drops to close to zero and bellow I need to crank for like 20secs. During spring, summer and half of autumn it starts with no problems. I tried many things at garages, and well someone told me recently an idea along the lines " maybe your plugs not receiving power, try to directly connect them to the the battery when hard start occurs". And here i am now with 3 plugs less:)
 
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When you are starting the car from cold, are you aware you have to wait for the glow plug light to go out before you crank the starter?
ie--
1. Turn ignition on, glow plug lights up.
2. Glow plug light goes out.
3.. Turn key to start position to crank engine.
 
Yes i know about that.
In short my hard start could be explained like this:
If temperature is low (anywhere from - to +5-8c) and i leave my car with hot engine (90c or so), then next morning it wont start easy.
If i leave my car with cold engine ( for example driving it for few mins to a shop and so on, engine doesn't reach working temp.), then it will start next morning no matter what ambient temp. is.

Pretty much at the dead end now with this problem, thinking it has to do something with expanding/shrinking of some parts, that makes some leaks or something.
 
Do you get any white smoke when it starts rough in the morning? Just a poof when the engine starts.


To me is sounds like when the car is left hot, the hot engine coolant is pressurised and expands so therefore some leaks into the cylinder bores and therefore it is difficult to start the next morning. Cracked cylinder head?

And the reason you didn’t notice this in the summer is because the cooler weather puts more strain on the battery during cranking...
 
Here is the whole process, the puff of white smoke comes at the end, but it looks like very small one( might just be normal from condensation?)



Also rarely car starts even on cold mornings (if I left engine hot at evening) with no problems, and sometimes it has problems starting at around 10+12c or so.
 
desertstorm said:
The glow plug nominal voltage is around 4.4V not like traditional glow plugs which are 12V . There is an electronic controller that applies 12V initially for a fraction of a second and then drops this down by altering the duty cycle of the applied 12V using Pulse Width Modulation to control the temperature.
This results in very fast warm up of the plugs but if you connect them to a 12V supply they will burn out in a second or two. Good job they are not a silly price. Look for Beru or NGK items.
Click to expand...
 
So audi a1 1.6d threw no2 error glow plug ,the one that was erroring was 7 ohms rest were .7ohms...with harness pulled off .note 12 volt test killed it ,luckily I had bought one ..12 euro each..ngk recommended, beru made orignal one.this post help explain voltage mystery...swop it to other cylinder if you need to be sure ..clear the error ,code should move to another cylinder if only one is bad...
 
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