L series glowplugs and glowplug dash light

Did a test yesterday with glowplugs and pre heat ,wired glowplugs direct to the battery ,it took just over 10 seconds for the tip to glow slightly on all .Glowplug dash light illuminates for just over 4 seconds .Which one is knackered ?

What did you use to earth the plug during the test? They draw a massive amount of current so the return path from the plug is very important.

Not sure if they're actually supposed to get to a glowing state within a couple of seconds though.

A typical glow plug draws around 12 to 15 Amps. Contrary to the name. They don't actually glow in use. They just get very hot. Making them glow with a 12 volt supply will shorten there life.

I'm waiting for a test meter to arrive so I can test them properly ,sure I read that someone had bought new ones and they glow up nicely ,prompting me to test mine and ask the question .

I must confess, I have done rather a lot of work on small marine diesels (practically all are derived from automotive engines) and the quick start parallel wired 12v glow plugs glow cherry red in around 2 -3 seconds. That is normal for the many I have worked with - however I have not tested specific freelander glowplugs.
I would also caution as to what kind of meter you are buying ? a normal multimeter will not take the current of the set of 4. As nodge said, 12 - 15 amps is normal - (I usually find 9 to 12 amps normal but there are obviously different types of plugs). Some plugs are rated at a lower voltage deliberately to increase heat up time and this is compensated for by the accurate timing of an electronic module.
I would also agree with B34R regarding a good quality earth !. This would be from the engine block to the battery - or block to chassis to battery. If in doubt, use a good jump lead from a good point on the block to the negative on the battery to test the earth.
A suitable meter to test the current flow would be a dc clamp meter Ammeter.
As to which one is knackered ? I would say absolutely none. A shorted plug would simply allow the preceding plugs to glow. An O/C plug would not glow while the others did.
Sounds like a poor positive feed or poor negative return.
Again, be cautious of dc amperage testing with multimeters !!!

When I was looking to rewire the glow plugs on my Series 2 1/4 - I was looking at fuse and relay rated to 70 amps - that's a considerable amount of power.

The fuse able link for the TD4 glow plugs is rated at 100 Amps. This would suggest an operating current of 50 Amps or so. This equates to 12.5 Amps per plug. Slightly more when the engine is running.

Nodge68 said:

The fuse able link for the TD4 glow plugs is rated at 100 Amps. This would suggest an operating current of 50 Amps or so. This equates to 12.5 Amps per plug. Slightly more when the engine is running.

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Agreed Nodge. We have to remember, the fuse protects the cable ! - never the component. - I believe the turn on surge current would be in the order of 50 A, however, would drop as the initial reactance surge decreased. The value of the fuse cannot be directly related to the surge of the circuit, or indeed, the continued load - only an approximation. Valid point though.
Joe

Here is a reasonable link - again, fuse size is purely to protect the wire - not the component - this is standard automotive (and indeed - electrical) practice.

One can only approximate the load related to the fuse - all you can deduce is that it is lower than the maximum expected - it also depends on the type of fuse. Don't forget !- the fuse is not rated at the current it will 'blow at' the rating is the current it can carry continuously..

Interesting site -

https://www.picoauto.com/library/automotive-guided-tests/glow-plugs

What's clever with the TD4 ECU is its plug drive software. It uses engine temperature to decide whether the plugs are needed and for how long. It then cross references the battery voltage, lengthening or shortening the temperature derived time as necessary to drive the plugs for exactly the correct time.

Nodge68 said:

What's clever with the TD4 ECU is its plug drive software. It uses engine temperature to decide whether the plugs are needed and for how long. It then cross references the battery voltage, lengthening or shortening the temperature derived time as necessary to drive the plugs for exactly the correct time.

Click to expand...

Absolutely Nodge. !! that is the key to the quick heat plugs.! a user using manual timing (or indeed TESTING !) could destroy the plugs in a matter of seconds over the desired time. And, as you say, the desired time is calculated form the various parameters available.
Quick heat plugs are fantastic, but NEED to be electronically controlled. In an ecu. ! without this - bang goes the plugs. !!

As for the dash light, well, this is a misleading signal - the dash light is only indicative of the time the circuit is SUPPOSED to be activated, not if it is effective.

Spot on mate !
Joe