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[Agemo]

Car has always started fine when cold, and when hot, but sometimes I want the plugs to come on & they don't. A mate of mine had a spare relay, so I fitted it. The car had been stood for an hour, so should have been cold enough to require glow plugs, BUT the light didn't come on. I replaced the relay with the old one, no light again. I discovered the 20 amp fuse under the bonnet had blown, so replaced it thinking that was the problem. No different, the glow plugs still won't fire up. when turning the ignition OFF, the glow plug light blinks. I am now stumped, any ideas?
 

[zirk]

Why do you want the plugs to come on when they shouldn't need to?

[Agemo]

Why do you want the plugs to come on when they shouldn't need to?

Sounds like I didn't explain properly. The car has stood for two hours now, and the plugs should come on, this means I can't even start the car.

[martin42]

glow plugs will only activate when its below a certain air temperature and engine temperature,if its not starting as it should then look at the leak off pipes as they could be letting air in

[zirk]

Ok, forget the light on the dash for the minute, are you getting 12v on top of the GP relay (6 black wires feeding the GP's or pull the top off and measure the pins), if dont have a voltmeter use a 12v bulb to negative. 12v should be there for about 5 sec from ing. on when Engine cold.

The i/p to the Relay is fed directly from the battery positive with a biggish fuse on the side of the relay, looks like a brass strip held in with 2 screws.

[Agemo]

Ok, forget the light on the dash for the minute, are you getting 12v on top of the GP relay (6 black wires feeding the GP's or pull the top off and measure the pins), if dont have a voltmeter use a 12v bulb to negative. 12v should be there for about 5 sec from ing. on when Engine cold.

The i/p to the Relay is fed directly from the battery positive with a biggish fuse on the side of the relay, looks like a brass strip held in with 2 screws.

I will nip out & put a meter on the pins, the brass strip bit is ok.

[zirk]

Ok, while your there, pull the top of the relay plug off and measure each GP lead to earth, should be 1 to 2 ohms each plug or open circuit if the pugs been cooked.

Wondering if your suffering the arched relay contact problem, any flat battery;s lately?

[Agemo]

OK, I have 3.5 volts at the pins, EVEN WITH IGN OFF! And yes, having flat battery, was going to replace.

[zirk]

3.5 Volts??, whats the Battery voltage, whats the voltage on the brass fuse, either side of it, if the fuse is 3.5 volts then could be cooked wiring or bad connection to the battery.

If 12v on the fuse then sounds like an arced relay problem, also kills battery quickly (fixable).

Go and have measure.

[Agemo]

Just checking now

[Agemo]

OK. 13 volts everywhere, (IGN off) both sides of the brass strip, and the battery. Terminals were cleaned a couple of weeks ago so good connection.

[zirk]

Is the 3.5v there with the GP plug on or off, either way sounds like arced relay contacts to me, pull the relay off and take it apart (small blade in at the bottom, probably end up braking the plastic clips dont worry).

Have a look at the 2 relay contact inside.

Got a pic somewhere will dig it out.

[Agemo]

Yep, 3.5 volts there all the time. I have two relays, taking one apart now.

[zirk]

See the pitted arc on the first contact

[Agemo]

Still not managed to get it apart yet, may have to go in the vice