[axton1964]

I too have a problem with Cold Start. As soon as the temperatures dip my initial cold start involves a 5 or 6 second crank before the engine fires.
I have already replaced glow plugs expecting this would be the problem as it has been on many other cars with the same problem. I have narrowed the fault down to the glow plug relay. When testing the relay all working fine, it’s the supply to the relay that doesn’t make sense. The main power through the relay to the glow plugs is ok, it’s the switching connections that are confusing. With ignition on one connector is showing 12 volts and the other connector is showing 3.5 volts! I would have expected this connector to be going to ground (not putting out 3.5 volts) to energise the relay and put the glow plugs on. I can’t find any other relays on the vehicle that would be to do with timing the glow plugs on so can only imagine they’re timed on by the ecu. I would be grateful of any input on this as I’m at a complete loss now.

[nzenigma]

From your description:

Relay coil works ok = 12v high side , 0v ground side. ...correct?

Relay contacts = 12v battery side ( via 80 Amp fuse), 3.5v glow plug side .

Therefore you have an 8.5v loss across the contacts.

Replace damaged relay.

[axton1964]

Hi thanks for your input.
Let me describe what I’ve found a bit better.
With the glow plugs relay removed probing the terminals below I have 12 volts on connector from battery through 80amp fuse, 0 volts on opposite large connector going to glow plugs, with ignition on 12 volts from the supply terminal for energising the relay and 3.5 volts on the terminal that lets the relay go to ground.
Hope this is a better description of what I’m finding.
I’m unsure as to how the glow plugs are timed on/off, as I said in my initial post can’t find a timer relay on the vehicle.

[sundiz]

If you can get your hands on current clamp meter, you could put that over the cable going to the glow plugs. Easy to see how much current and how long the glow plugs work.

[axton1964]

Hi, I’m quite sure there is nothing at all going to the glow plugs. There’s nil voltage drop across the battery when the ignition is switched on with a cold engine. It’s as if the relay is not switching them on. My suspicion is that the relay connector that’s putting out 3.5 volts should in fact be going to ground through a timer relay or the ecu.

[nzenigma]

"My suspicion is that the relay connector that’s putting out 3.5 volts should in fact be going to ground"

true it is ECU controlled and in your climate may activate periodically. The 3.5V may be cct leakage. I dont have the diesel data at my finger tips.

Lets see if old mate @tw2005  has the glow cct. Or has already posted it.

[Paolo39]

That is all, what I found from Service Manual. Does not say anything about voltages on relay.

[nzenigma]

Hi, I’m quite sure there is nothing at all going to the glow plugs.

Meanwhile, to confirm, have you clipped your meter to the glow plug rail and watched for a reading when first turning ignition on  = 9v?
Have you Done the same to rail feed wire while it is disconnected from the rail.?  =12v?
If no reading slip fuse wire under relay leg and repeat, or follow directions as per Paolo's pages.

[nzenigma]

Thanks Paolo  we hit the button at the same time.

the rest is up to axton.

[electroman5000]

Hi Axton!

Any luck with sorting out the glowplug issue?

There is information that if a common rail pressure sensor is dodgy, then it could be the problem with poor engine start. Might be something worth checking out as well.

Cheers!

[axton1964]

No still no joy unfortunately, I’ve tried some of the great suggestions from previous posts but still no power at the glow plugs at all. I have managed to get power to the glow plugs by connecting the wire from the relay that’s currently giving a voltage of 3.5 volts to earth and switching the ignition on.
Im interested to know what switches the glow plug relay to ground, if it’s the ecu alone then perhaps it’s the ecu at fault.🤔

[nzenigma]

Ecu 'grounds' the relay.

There is information that if a common rail pressure sensor is dodgy, then it could be the problem with poor engine start.

    Just turning ignition on, not cranking yet, not at the stage of reading pressure.

[axton1964]

Yes I suspect either the ecu or whatever supplies the ecu with temperature information, I have tested and replaced the coolant temperature sensor anyway.

[nzenigma]

Yes I suspect either the ecu or whatever supplies the ecu with temperature information, I have tested and replaced the coolant temperature sensor anyway.

Probably you are at the stage where you need a workshop scanner. Read any codes and live data.

If it is Ecu....= $$$$..... employ the old push button under the dash trick or a $5 timer from China.

[plasticphyte]

Might be relevant, might not be, but if your vehicle has been running diesel for some time, and no anti-diesel bug has ever passed through it, you could have a clogged fuel pickup (the pre-filter in the tank) that needs a good cleaning. Failing that, there could be an issue with the fuel pump losing pressure when the car is sitting out.

I recently had run into an issue with my car (2012 GD) starting to take 5-10seconds to crank over when cold, and it would only crank once I applied a little squeeze on the throttle, then it would idle rough for a few moments.
Service centre had recently done the fuel filter replacement, so thought it might have been related to that, took it back, they checked some stuff out, found the fuel pickup was basically green with gunk, cleaned it, and it's been starting right as rain since.