Glow Plug Diagnostics

Simon,

The make and year of your vehicle would help.

Not all diesels are the same.

Wayne

It is pretty easy to check the glowplugs in the vehicle.
Remove the busbar or wiring connected to the glowplug tips, either a nut or wiring connector depending on engine brand and type.
Get a testlamp, connect the fly lead to positive battery.
Touch the probe on test lamp to each glowplug wiring connection in turn, if the testlamp lights up then the plug is ok, if no light the glowplug is open circuit and no good. They usually go open circuit when blown.
Most indirect injection engines (Toyota 2H, 1HZ etc) will need at least half the glowplugs working to get a cold start.
Most direct injection engines (usually late model turbo engines) will quite often start without any functioning glowplugs unless really cold.
Unless the glowplug tip is broken off or badly swollen or blistered it is very hard to tell condition visually.

Ill take the guess that its a 3.0 Patrol starting to do the usual in No3.

A fool proof test for glow plugs is to test their resistance which will also identify extremely lazy ones that will stuff your cold starts. It doesnt have to be completely cactus to affect your starts.

1. set your multi meter to the 200ohm setting.
2. disconnect and remove the bar that ties all the glow plugs together.
3. At this point all the glow plugs are still mounted in the head with nothing connected to them
4. with one probe firmly gouged on the top of the plug and the other probe gouged into the side of the plug to get a good earth check the readings of each individual plug.

The reading will show some where aroun 006 give or take depending on the brand of plug this can vary a reasonable amount however they should all be around the same. If most show 006-009 and one shows 025 or 1.0 or in between then thats the culprit. You can just replace the one but most people prefer to replace the set. Prices vary between $18 to $35 per plug depending on the vehicle, voltage and brand.

This is a ten minute job and is fool proof to solving the issue every time as too much resistance can stuff up cold starts easily. the plug doesnt necessarily have to be blown but this will identify that as well by your readings.

Hope this helps.

Glow plugs only aid starting, In your description you said it also smokes a lot when working hard, definately NOT glow plug issue, must be injectors or fuel pump.
Shane

Thanks for all the great advice on how to check the plugs, I will keep these for future reference. I'd had the system checked but they did not remove the plugs, probably used your method listed here. When I removed them for inspection I found the white/brown goo on the shank of the glow plug from No.3 cylinder and was concerned I had found the cause of the smoke being the start of a leak in the head gasket. However I have since realised that that area of the plug is above the mating surface with the head and therefore not in the cylinder, bang goes that theory!(no visible contamination of the oil, or loss of coolant) I also suspect the injectors & will investigate. Will also get the cooling system pressure tested...just to be on the safe side. PS: TD2.5 JEEP XJ Cherokee. Cheers, Simon.