glow plugs testing

Yoramy
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glow plugs testing

Post by Yoramy » Mon Dec 26, 2016 3:21 pm

Hi
In my Westerly Conway ketch the OM636 has 4 glow plugs connected in serial. Since it has been difficult to start the engine from cold but never from warm, I started testing them. I pulled out the first in the series and tested it for Ohm (no reaction) and by running power directly to it from the batteries (which may have been a mistake since it needs 9V, not 12V), and it did not glow. I had a spare plug, tested it the same way and it glowed so I placed it in the chamber instead of the bad one.
I then tried to establish if current is running at all to the live wire at the plug when the ignition switch is in the glow position - ignition key a notch clockwise + a springed press. So far I could not see on my voltmeter power arriving at the first glowplug, the one I assured is glowing. the wire running into this plug is coming from what seems to be a resistor, resting on a bracket with a couple other components. the wires running into this resistor also do not show any current when the switch is in glow position.
I wonder if anyone has more knowledge about this - which component on the bracket is the resistor supplying the glow plugs and which incoming wire on the relevant element should show current when the switch is in glow position?
I'd like to replace this system with a more modern one, connected in parallel and using 12V, offered by Westfield http://www.west4x4.demonweb.co.uk/om636 but I first want to verify what the problem is. Here are images of the first and last plugs in the series as well as the bracket
I also found a detailed PDF description of how the system is wired and tested but I still cannot determone the source of the problem
http://www.170v.de/yabbfiles/Attachments/Preheating.pdf
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OM636 ignition bracket-113.jpg
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tuskerknee
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glow plugs testing

Post by tuskerknee » Tue Dec 27, 2016 8:29 am

Hi Yoramy,

The component marked "Hella" looks like a relay, used to protect the ignition switch from the high current used by the glow plugs. There should be one or two thin wires coming from the ignition switch. When you activate the glow plugs at the ignition switch, this applies 12v to a coil in the relay. The coil closes a heavy duty switch inside the relay the connects the two brown wires together and passes 12V to the resistor. I suspect the brown wire attached to the terminal facing the camera should have 12V on it.

It's hard to say definitely what the black box with a silver knurled nut is, but it reminds me of an old fuse box I once had on a previous boat. Undo the nut and lift off the black cover, and you might see two fuses inside.


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steve parry
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Re: glow plugs testing

Post by steve parry » Tue Dec 27, 2016 12:37 pm

HI,

I had the same problem two years ago but on a Volvo MD 2030, it turned out to be the relay was duff thus not producing the power to heat up the plugs. It was a sod to start until I changed the relay (£3 bit) but now starts first time every time.

Regards

Steve

Yoramy
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Re: glow plugs testing

Post by Yoramy » Thu Dec 29, 2016 7:27 am

Thank you for the information
I tested the brown wire at the top of the Hella relay for current but did not see it is getting any, in any of the ignition switch positions (other than the last, the starter position). I guess the next stop up the line is the ignition switch itself, although starting is never a problem from warm so the switch is properly closing the circuit for the starter to run. Not sure about the glowplugs switch position functionality. If the switch is closing a circuit for the starter, does it mean the glowplugs circuit is closed as well? I believe the diagram shows that power to the glowplugs is cut when the switch is moved to the starter position, to allow enough current to get to the starter.

there are indeed 2 fuses in the black box. not sure if they are in working order because the copper strip is severed on both - see image. Is this the way these fuses should work? they are marked 40/25.

Thanks
fuses 155.jpg
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Re: glow plugs testing

Post by philipstevens » Thu Dec 29, 2016 8:55 am

The "copper strips" are the fuse "wire".

As both are blown, you need to find out why.

It could be that the relay has gone short circuit/burnt out, and that has blown the fuses.

You may find that you have voltage one side of the fuse holder when you operate the ignition switch. If so, then the relay is at fault.

You may see the fuse size on the underside of the fuses - looking at the wire, I would think 20A, but check. I think 5A or 10A would be high enough, as they are only there to protect the wires if the relay short circuits.

The relay is a 60A Hella http://www.rallylights.com/hella-h43710 ... acket.html. You should be able to get a new one from an auto specialist shop - maybe Halfords, but don't hold your breath!

So, check if you are getting a voltage on the fuse holder block. If so. fit a new relay with new fuses (get a couple of spares as well).
regards,
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Yoramy
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Re: glow plugs testing

Post by Yoramy » Thu Dec 29, 2016 12:40 pm

Thank you Philip
there is voltage at the fuse holder when the switch is on - at the wires on the upper section of the image, those covered with black sleeve. it means the fuses come before the relay I presume, and if so, a burnt relay would not affect the fuses. Is that correct?
Also, why are there 2 fuses?
and how come the starter runs and the engine starts if the fuses are burnt ? are they not related to the starting sequence other than to supply the glowplugs?
I'll install new fuses now and check if the relay gets and sends any voltage.
they underside of the fuses is marked 40/25 - so that's 40Amps 25W?

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Re: glow plugs testing

Post by philipstevens » Thu Dec 29, 2016 3:41 pm

Looking at your photos again, it looks as though the red and black are the relay operating supply, and the two brown wires are for the heaters.

Before you put in new fuses, check that you are getting 12v on the red and black when operating the ignition switch - and if there are two of you doing the testing, make sure that you can either hear or feel the relay operating.

The 12v at the fuses, may be a red herring! The fuses may have nothing to do with the heaters - not being able to see exactly where all the wires go and come from. You will have to trace where the heater wires come from, and where the fuse wires go to.

Your relay will have four terminals - red and black for operating the relay, and two brown wires. One brown with voltage on it, and the other going to the heaters. You only need to use one probe of your tester for voltage - the black probe can be clipped to the engine block, the -ve. That will leave you with just the +ve/red probe to check voltages with. Easier than holding two probes on different terminals.

The fuses may be in the heaters circuit having a voltage on one side of the fuse holder. This could be why they have blown - the heaters having a short circuit fault.

If you have one good heater, disconnect the others, and then when you put new fuses in, the fuses may not blow when you operate the ignition switch. If all goes well here, then one of the other heaters may be at fault. You should get a resistance reading from the heaters - not a zero reading.

If you have a chance to take another photo or two of the fuse/relay area, it would help to post it. I'll assist if I can - I fitted an intake heater to the Bukh in a previous Konsort.
regards,
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Re: glow plugs testing

Post by tuskerknee » Fri Dec 30, 2016 12:42 am

If the two brown and white wires are both connected to the upper terminal of the relay, it could be that a previous owner used two lower current-rated wires to supply the required current for the heaters. That would mean the voltage is on the side with the taped brown and white wires, the fuses have done their job and blown for some reason, cutting off the voltage to the upper terminal of the relay, and nothing gets to the heater when the relay operates.

If the two brown and white wires go somewhere else, ignore this.


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Re: glow plugs testing

Post by philipstevens » Fri Dec 30, 2016 2:22 am

Good point concerning the two brown and white cables. They could well go to one terminal on the relay.

But why the fuses blew, still needs to be addressed.



Comprehensive glow-plug information http://www.beru.com/download/produkte/TI04_en.pdf
and testing http://mechanics.stackexchange.com/ques ... glow-plugs
regards,
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Re: glow plugs testing

Post by tuskerknee » Fri Dec 30, 2016 2:59 pm

I agree with you, Philip. Wherever the brown/white wires go, they should be traced to work out why the fuses blew. If they are 40 amp fuses in parallel, there must have been more than 80 amps going through them at some point. [emoji45]


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Re: glow plugs testing

Post by Yoramy » Tue Jan 03, 2017 5:55 am

Yes indeed the two brown/white wires from the fuse holder go to a single terminal on the relay.
The relay has 4 terminals:
from the fuse holder (brown/white)
to the resistor (brown)
from the battery plus? (red)
to ground on engine block (black)

these fuses are hard to get. I'm still trying to find some. 80 amps went through them, I wonder how could this have happened. would heating for too long cause that?
next i'll check resistance on the remaining 3 plugs to see if the plugs themselves have a short (reading = no short), then see if the metal rods connecting them although it seems they are clearly not touching the engine block.
one plug is certainly good so when the others are out and the switch is in heat position the fuses should not blow
I think I will have however to buy a new set of 4 plugs connected in parallel (without the resistor)

here are some images to make sure I got it right

Thank you for your advice
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Re: glow plugs testing

Post by philipstevens » Tue Jan 03, 2017 9:46 am

The fuses could be 40V 25A. If so, they are old automotive Bosch Type GBC fuses. The highest rating I could find was 25A.

http://www.12voltplanet.co.uk/continent ... fuses.html

If you want to replace the fuse holder, all I can find is a four-way block. http://www.12voltplanet.co.uk/continent ... 4-way.html

As you say, difficult to get hold of as they are rarely used - only on older cars etc.

The fuses are there to protect the smaller size wire.

Carry on as you are going, using the one good heater to start with.
regards,
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Re: glow plugs testing

Post by tuskerknee » Tue Jan 03, 2017 4:32 pm

Yoramy wrote:Yes indeed the two brown/white wires from the fuse holder go to a single terminal on the relay.
The relay has 4 terminals:
from the fuse holder (brown/white)
to the resistor (brown)
from the battery plus? (red)
to ground on engine block (
Hi Yoramy,

I think the red wire should go to the ignition switch position that turns the glow plugs on, rather than directly to the battery plus.

Hope you manage to get the problem resolved.

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Re: glow plugs testing

Post by BrightStar » Tue Jan 03, 2017 9:06 pm

A slight deviation, has anyone fitted a thermostart into the inlet manifold on an MD7A, seems fairly straight forward and not expensive as a starting aid. On the other hand is it wise to have a flamethrower mounted in the engine intake.
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Re: glow plugs testing

Post by BrightStar » Tue Jan 03, 2017 9:06 pm

A slight deviation, has anyone fitted a thermostart into the inlet manifold on an MD7A, seems fairly straight forward and not expensive as a starting aid. On the other hand is it wise to have a flamethrower mounted in the engine intake.
Brightstar
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