Cold Start Issues - Constant Voltage to Glow Plugs While Off

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stevesmiff
Posts: 13
Joined: Fri Nov 26, 2010 10:17 am
Currently Drives:: Megane 1.5 dCi 100 Dynamique 5dr

Cold Start Issues - Constant Voltage to Glow Plugs While Off

Postby stevesmiff » Sat Jan 05, 2013 11:25 pm

My Megane 1.5 dCi started having cold start issues a few months ago. Did some simple multimeter checks on the glow plugs and found 2 of 4 were dud. I replaced all 4 and all seemed well.

A month down the line, the car is struggling to start on a cold morning. The other day it was about 4C outside and it took three attempts to start and when it did, it chucked out a load of smoke.

I've put my multimeter on the plugs and they all seem okay. Tried measuring the voltage going to the plugs while starting, which also seems fine. I then turned off the ignition and noticed that there was still 10.5v going to the plugs?

This is really confusing as if it was sending 10.5v to my plugs all night then surely I'd have a flat battery and also my plugs would be fried. My checks are not showing this but my car struggles to start the colder it is whilst chucking out smoke. Really confused - any help appreciated.

AlexB
Driving Legend
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Joined: Tue Mar 22, 2005 8:17 pm
Currently Drives:: Renaultsport R.S.250 Cup

Re: Cold Start Issues - Constant Voltage to Glow Plugs While

Postby AlexB » Mon Jan 07, 2013 10:42 am

The battery is not flat because the plugs are in broken connection state... The voltage you see is the testing voltage the ECU uses to detect dead plugs. It is my guess... Another option is disconnected ground wire, but then the starter wouldn't be working - so it is unlikely.
AlexB
(no, a different AlexB)

stevesmiff
Posts: 13
Joined: Fri Nov 26, 2010 10:17 am
Currently Drives:: Megane 1.5 dCi 100 Dynamique 5dr

Re: Cold Start Issues - Constant Voltage to Glow Plugs While

Postby stevesmiff » Mon Jan 07, 2013 12:29 pm

I also thought the voltage I was seeing might be some kind of test by the ECU but I measured it once then came back 5 min later and it was still showing the 10.5V (approx) reading the whole time. Surely the ECU doesn't test the plugs for that long?

Also, I don't understand your term "broken state". My (very) limited knowledge says to me that if I am reading 10.5v coming out of the glow plug connector then the battery is using that power. Obviously my battery isn't going flat and my glow plugs don't appear to be fried so what you say is obviously correct but just want to know in Layman's terms what you mean. I haven't heard anyone else talk about this constant voltage so just all seems a bit confusing to me?

Thanks for your help.

AlexB
Driving Legend
Posts: 4312
Joined: Tue Mar 22, 2005 8:17 pm
Currently Drives:: Renaultsport R.S.250 Cup

Re: Cold Start Issues - Constant Voltage to Glow Plugs While

Postby AlexB » Tue Jan 08, 2013 1:42 pm

I wrote "broken connection state" meaning that the circuit is disconnected due to a lost contact or blown plug. In such a case the voltage will not cause any current.

So, if you take a measurement from the contact while the plug is disconnected - it is the broken connection circuit. It may easily happen that inside the ECU this circuit is connected to +12V with a very large resistor, e.g. 50k. In such a case, when connected to the plug, the voltage on the plug will be next to 0V, but when disconnected it will be just below 12V (depending on the internal resistance of your voltmeter).
AlexB
(no, a different AlexB)

stevesmiff
Posts: 13
Joined: Fri Nov 26, 2010 10:17 am
Currently Drives:: Megane 1.5 dCi 100 Dynamique 5dr

Re: Cold Start Issues - Constant Voltage to Glow Plugs While

Postby stevesmiff » Tue Jan 08, 2013 4:55 pm

Ok - I sort of get you now!

Just to clarify, the 10.5v reading I am getting is taken from the connector itself while detached from the glow plug. The glow plug remains in its fitted position but was not part of this specific test.

Should I assume that from what you are saying, someone with the same vehicle as me should therefore experience the same 10.5v (approx) while off situation as me whilst reading a disconnected lead? If so, is there any 1.5dCi owners that can confirm this?

furcipus
Posts: 1
Joined: Mon Mar 05, 2018 1:09 am

Re: Cold Start Issues - Constant Voltage to Glow Plugs While Off

Postby furcipus » Mon Mar 05, 2018 1:11 am

I can confirm, i have measured also the 10.5V at my Dci 1.5 - K9K engine, its in an Nissan Almera N16.

By the way, i have starting problems, i think my glowplugs glow to short. And i search for a solution to enhance the "glow time". (Temperature sensor!?)

The car is just starting, when the "coil symbol" is lighting up for 1 second. Just during that second, there is the timeframe to start the engine.


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