Glowplug help please

Thanks for everything. In the end I removed all 3 glowplugs and measured the resistance away from the engine. I got inconsistent results with the plugs in situ, due to awkward positioning.
The result was that all 3 measured between 25-35ohms, with the target of a good plug being <1. So all plugs are duff. 3 new plugs are winging their way to me as I speak.
The one bit I still don’t understand is the GP rail voltage at 11.3ish, and a battery terminal V of 12.6v. But a poster above also said he had 11.6v at the rail with the same engine. Mmmmm not sure if I need to look further into that or just accept it. ?
Thanks to all posters once again.

Mike.
 
Mickyfinn said:
Thanks for everything. In the end I removed all 3 glowplugs and measured the resistance away from the engine. I got inconsistent results with the plugs in situ, due to awkward positioning.
The result was that all 3 measured between 25-35ohms, with the target of a good plug being <1. So all plugs are duff. 3 new plugs are winging their way to me as I speak.
The one bit I still don’t understand is the GP rail voltage at 11.3ish, and a battery terminal V of 12.6v. But a poster above also said he had 11.6v at the rail with the same engine. Mmmmm not sure if I need to look further into that or just accept it. ?
Thanks to all posters once again.

Mike.
Click to expand...

That needs investigation.

If you were observing that much volts drop due to the current flowing through your 3 duff glowplugs it is going to be much higher with three good ones installed

Have you checked those voltages with all three glowplugs removed ? If you still see that difference then there is a seriously bad connection somewhere other than in the glowplug circuit.
 
Mickyfinn said:
Thanks for everything. In the end I removed all 3 glowplugs and measured the resistance away from the engine. I got inconsistent results with the plugs in situ, due to awkward positioning.
The result was that all 3 measured between 25-35ohms, with the target of a good plug being <1. So all plugs are duff. 3 new plugs are winging their way to me as I speak.
The one bit I still don’t understand is the GP rail voltage at 11.3ish, and a battery terminal V of 12.6v. But a poster above also said he had 11.6v at the rail with the same engine. Mmmmm not sure if I need to look further into that or just accept it. ?
Thanks to all posters once again.

Mike.
Click to expand...

What I realise I should have also checked was the voltage at the solenoid when the glow plugs were ‘on’. There might not have been such a voltage drop in the relay and wiring as I suspected or appeared to measure.
 
john_morris_uk said:
What I realise I should have also checked was the voltage at the solenoid when the glow plugs were ‘on’. There might not have been such a voltage drop in the relay and wiring as I suspected or appeared to measure.
Click to expand...

In #14 you say , "Quick update. Battery voltage 12.6 volts measured at the starter motor solenoid. 11.6 volts on glowplug rail when glowplug on." but what was the voltage at the starter solenoid when the glow plugs were on. That would be a more relevant figure to compare with the volts at the glow plugs than the figure without them on.
 
VicS said:
In #14 you say , "Quick update. Battery voltage 12.6 volts measured at the starter motor solenoid. 11.6 volts on glowplug rail when glowplug on." but what was the voltage at the starter solenoid when the glow plugs were on. That would be a more relevant figure to compare with the volts at the glow plugs than the figure without them on.
Click to expand...

Yes, it would. But the glowplugs are designed to operate at a voltage lower than 12v, so I don't think it's a major problem. The 3 glowplugs draw about 20A between them, and the engine loom wiring is only 2.5 mm², so there's bound to be a bit of voltage drop, but it won't affect working glowplugs.
 
pvb said:
Yes, it would. But the glowplugs are designed to operate at a voltage lower than 12v, so I don't think it's a major problem. The 3 glowplugs draw about 20A between them, and the engine loom wiring is only 2.5 mm², so there's bound to be a bit of voltage drop, but it won't affect working glowplugs.
Click to expand...

But if Micky Finn is seeing a volts drop of about 1.3 volts with 3 duff glowplugs , probably drawing little more than 1 amp between them, the volts drop with 3 new ones potentially drawing 20 amps is certainly going to affect them.
 
VicS said:
But if Micky Finn is seeing a volts drop of about 1.3 volts with 3 duff glowplugs , probably drawing little more than 1 amp between them, the volts drop with 3 new ones potentially drawing 20 amps is certainly going to affect them.
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Let's wait and see what happens when his new glowplugs are fitted.
 
VicS said:
In #14 you say , "Quick update. Battery voltage 12.6 volts measured at the starter motor solenoid. 11.6 volts on glowplug rail when glowplug on." but what was the voltage at the starter solenoid when the glow plugs were on. That would be a more relevant figure to compare with the volts at the glow plugs than the figure without them on.
Click to expand...

That’s exactly the point I was making. I was apologising for not thinking to measure while under load.
 
Last edited:
OK, I.ve got three new glow plugs, and the resistance net of the meter resistance is 1ohm. (compared to 20-40ohm of the old GP's.)

I'll fit them maybe tonight, and measure the rail voltage with plugs on to see if it is higher than with the duff plugs!
Watch this space !
Mike
 
Mickyfinn said:
OK, I.ve got three new glow plugs, and the resistance net of the meter resistance is 1ohm. (compared to 20-40ohm of the old GP's.)

I'll fit them maybe tonight, and measure the rail voltage with plugs on to see if it is higher than with the duff plugs!
Watch this space !
Mike
Click to expand...

If nothing else has changed I'd expect it to be lower. If it is higher that will be difficult to explain!
 
Ok........ new glowplugs fitted (one of the only “5 minute jobs” I’ve ever done! And tested. Rail voltage has not changed, still 11.3 ish, but the engine burst into life with great enthusiasm almost before I pressed the start button!
So all’s well.
I’m am still puzzled by the rail voltage at 11.3 tho. Someone suggested above that the plugs are rated at 11.5v. Why would that be?

Grateful thanks to all of u for contribution and chat.
 
Mickyfinn said:
I’m am still puzzled by the rail voltage at 11.3 tho. Someone suggested above that the plugs are rated at 11.5v. Why would that be?
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I said in post #24 that the plugs have a rated voltage of 10.5v. You have more than that. The engine starts. Stop worrying!
 
Mickyfinn said:
Ok........ new glowplugs fitted (one of the only “5 minute jobs” I’ve ever done! And tested. Rail voltage has not changed, still 11.3 ish, but the engine burst into life with great enthusiasm almost before I pressed the start button!
So all’s well.
I’m am still puzzled by the rail voltage at 11.3 tho. Someone suggested above that the plugs are rated at 11.5v. Why would that be?

Grateful thanks to all of u for contribution and chat.
Click to expand...

I am puzzled by the fact that the rail voltage has not changed now that you have replaced 3 duff glow-plugs with 3 new ones, which should be drawing a much greater current but I am uncertain about where, when and how you are making your measurements.

They are rated at 10.5 volts as pvb says. You will find that fact in the workshop manual !

The reason for the low voltage rating may be because when the engine is being cranked the battery terminal voltage could fall as low as that, assuming the battery is the recommended size, not something very much larger
 
I measured rail voltage between the battery neg terminal and the + connection to the rail, glowplugs ON, engine NOT cranked. I used a multimeter on 20v dc scale.
Why would the rated V of the plugs be 10.5v ....... the engine is not cranked till after the plugs are off? So there is no cranking v drop while plugs are ON

The original engine battery was 95Ah but has been replaced with 110Ah. Battery new last year, terminal resting V is 12.6v

I know it now works, “so don’t overthink the problem”, but I’m puzzled.
 
Mickyfinn said:
I measured rail voltage between the battery neg terminal and the + connection to the rail, glowplugs ON, engine NOT cranked. I used a multimeter on 20v dc scale.
Why would the rated V of the plugs be 10.5v ....... the engine is not cranked till after the plugs are off? So there is no cranking v drop while plugs are ON [/COLOR]

The original engine battery was 95Ah but has been replaced with 110Ah. Battery new last year, terminal resting V is 12.6v

I know it now works, “so don’t overthink the problem”, but I’m puzzled.
Click to expand...

You are comparing the volts at the glow-plugs with the rested battery volts . The relevant comparison would have been with the battery terminal volts while the glow-plugs were energised.
(If you had measured the actual volts drop between battery positive and the glow-plugs, as I suggested earlier, instead of always measuring from battery neg the confusion would not have arisen.)

If you look at the wiring diagram you will find that the glow pugs are also energised while the engine is being cranked. The relay is energised either directly from the key-switch or from the start button, via a diode, with the key-less panel.

According to the owners manual the recommended starter battery is 70Ah.
A resting volts of 12.6 is not fully charged but perhaps all you will achieve any more if you don't have a more modern high output alternator or some form of enhanced alternator regulation.
 
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