Watt voltage?

Question relating to my 1997 300tdi auto discovery with EDC please...

Turns over sluggish and just about fires up.

Background...
Newish battery. Key on accessory position I'm seeing 12.5v, ignition ON position I'm seeing 11.5v which stays at that level after glow plugs turn off. 14.1v when running.
Why does voltage drop from 12.5 to 11.5 when ignition on and before starting?

I'm sure you mean "What" not "Watt". HTH.

300bhp/ton said:

I'm sure you mean "What" not "Watt". HTH.

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It's called a "pun" HTH ; -)

darland said:

It's called a "pun" HTH ; -)

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No, sarcasm....

As ever, check all earths, and replace any that look slightly dodgy ..

Checks as @Paul D has advised. The glow plugs are quite a heavy electrical load, so you can expect the battery volts to drop slightly while they're activated.
Unlike the D2 where the glow plug circuit is controlled by coolant temperature through the engine ECU, the Disco 1 uses a plain old timer relay to trigger them instead.

brian47 said:

Checks as @Paul D has advised. The glow plugs are quite a heavy electrical load, so you can expect the battery volts to drop slightly while they're activated.
Unlike the D2 where the glow plug circuit is controlled by coolant temperature through the engine ECU, the Disco 1 uses a plain old timer relay to trigger them instead.

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Thanks I will check the earths. So should I expect the voltage to increase back to 12.5 ish once the plugs have deactivated. After 20 seconds or so?

darland said:

Thanks I will check the earths. So should I expect the voltage to increase back to 12.5 ish once the plugs have deactivated. After 20 seconds or so?

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Are you sure the gps are off when measuring? Don't know about your truck but some still energize after the dash light has gone out for a short while.

Flossie said:

Are you sure the gps are off when measuring? Don't know about your truck but some still energize after the dash light has gone out for a short while.

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Good question. I've heard they stay on for a while after the gp light extinguishes so I'm wondering if they are staying on . 11.5v doesn't seem to be enough to spin the engine sufficiently fast. How do I establish whether the gps are turning off?

...or if someone could kindly tell me where I'll find the gp relay I'll investigate?

darland said:

...or if someone could kindly tell me where I'll find the gp relay I'll investigate?

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Listen for a click and the dash lamps brightening, my 200Tdi sees the lamp extinguish after 11 seconds and relay times out at 35 seconds.

dieseldog69 said:

Listen for a click and the dash lamps brightening, my 200Tdi sees the lamp extinguish after 11 seconds and relay times out at 35 seconds.

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Cheers.

Oh and go to Halfords, pick up a new earth lead, you need to fit that at the chassis bolt that the battery mounts to and then use one of the bolts on the timing case to give direct connection to the engine to ensure you have the best earth connection.

Mine is mounted like so, not the black one that is going to my second alternator but the braided earth lead that you can see disappearing off along the chassis rail to the battery earth lead chassis bolt.

dieseldog69 said:

Oh and go to Halfords, pick up a new earth lead, you need to fit that at the chassis bolt that the battery mounts to and then use one of the bolts on the timing case to give direct connection to the engine to ensure you have the best earth connection.

Mine is mounted like so, not the black one that is going to my second alternator but the braided earth lead that you can see disappearing off along the chassis rail to the battery earth lead chassis bolt.

View attachment 160427

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Thank you

dieseldog69 said:

Oh and go to Halfords, pick up a new earth lead, you need to fit that at the chassis bolt that the battery mounts to and then use one of the bolts on the timing case to give direct connection to the engine to ensure you have the best earth connection.

Mine is mounted like so, not the black one that is going to my second alternator but the braided earth lead that you can see disappearing off along the chassis rail to the battery earth lead chassis bolt.

View attachment 160427

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Earthing through the chassis/body/frame isn't a good idea as time goes by, especially in higher power circuits.
Connections can corrode or oxidise leading to poor connections or even complete failure.
Flat braided cable is better for the connection between the chassis or body and the engine since it's more able to cope with any vibration but even a length of 50 square millimetre can improve poor earth problems if you have nothing else.
When I was gainfully employed as a radio technician I often cut a couple of lengths of heavy duty coaxial cable (not TV aerial cable) and stripped the middle bit out to use the braid as an earth connection on various bits of kit.

As a footnote to this thread it seems the glow plug relay was staying on. A replacement now shows voltages much more as expected.

Thanks to all (even 300bhp/ton ;-) )

I think I've cooked my battery though so looking for a quality replacement - optima red?