Cold start problems

[ChrisGoulding]

Whilst I was 'playing' with it last week, I did 2 things. Firstly, I disconnected the G72 sensor which made the glow plugs come on for well over 12 seconds. The second thing I did was to trick the car into thinking it was colder by taking the G72 sensor out and putting it a pot of ice scrappings from the freezer (my missus was not best pleased as she had to clean the oily handprints of the doors!!!). I checked the glow plugs again and they stayed on a lot longer, although not as long as unplugging the sensor. Presumably the G72 sensor is the one controlling the relay and timings etc. I cant believe that the engine would have to be frozen solid for the glow plugs to be kept on longer.

[kite]

Could your G72 be faulty, is it expensive to replace.

[ChrisGoulding]

The G72 sensor was only £15 to change and the instrument display is showing that the engine gets to around 90 degrees. It is one of the newer 'green top' ones and I suppose it could be faulty, but VAG-COM doesnt throw any codes out. VAG-COM did say it was faulty PRIOR to me changing it, but doesn't since I have changed it. Do you know where the timing relay is located as I may change that as well just in case, but to be honest, I suspect that it is working correctly. [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

[ChrisGoulding]

Yesterday I got in the car after it had been stood for over 12 hours. It was freezing and the windows were covered in ice and the display said it was minus 1.5 degrees!!!! I turned the ignition on and the glow plug light came on for 2 seconds and then went out. About 2 or 3 seconds later I heard a click and the lights dimmed a bit, which I think was the glow plugs actually turning off as I know they do stay on for a bit after the light has gone out. I turned the ignition and yet again it struggled to start. It had to turn over for 3 or 4 times and didn't sound too happy. It feels like the glow plugs haven't been on long enough. Even if I turn the key on and off several times, it isnt long enough to heat the plugs as they take 2 or 3 seconds to get hot and then cool off within 2 seconds hence why that method is not working. Any ideas now??? [img]/ubbthreads/images/graemlins/confused.gif[/img]

[kite]

Do you trust the display on the DIS, could it have been colder outside than the display was showing, what sensor does the DIS use for the outside temp. Could this be where the glowplug relay is getting its info, and tricking the system into thinking it warmer outside than it is.

[ChrisGoulding]

I may be wrong, but isnt the sensor for the DIS completely seperate to the engine temp? I was under the impression that the G62 sensor (sorry I kept calling it a G72) sent the signal for the relay. It is definately not right though whatever it is and it is P*#*$NG me right off!!!!! [img]/ubbthreads/images/graemlins/mad.gif[/img]

[kite]

Does the glowplug relay get its info from the G62 or the DIS sensor,what about swopping the relay, is the car battery good.
I had a Citroen diesel [img]/ubbthreads/images/graemlins/blush.gif[/img] with starting probs and a new battery cured that.

[ChrisGoulding]

I think it gets it from the G62 sensor. I have had the battery checked and it is fine. I am not sure where the relay is to change it. I cant think it can be anything else, although I have just read another article on another forum which says that it may be the contacts on the battery and/or starter may need cleaning to get a better contact. Who knows? I certainly dont!!!!!

[S3Quattro]

Have you checked there is 12V at the glow plug connection? If not check the glow plug relay J52. Its under the dash in the drivers footwell. This relay is controlled from the Engine ECU and doesn't have a timer built in. The G62 engine temp sensor is connected to the ECU. The G2 side of this twin sensor is connected to the dash panel temperature instrument. The glow plug lamp is also connected to the ECU.
Hope this info helps!!!!

[ChrisGoulding]

Although there is power going to the glow plugs, could the relay be faulty in that the ecu is telling it to operate, the relay turns on, but then turns itself off even though the ecu is still telling it to be on? Does that make any sense? [img]/ubbthreads/images/graemlins/grin.gif[/img]