Easy way to tell what glow plug may be down without glowlamp coming back on?

[pcman_jh]

My 1999 E300TD is smokey first thing in the morning for a few seconds (see other thread), and just over the last 2 days when it's been colder, it's been lumpy as if one of the glow plugs is down. There's no lamp in the instrument console coming back on, but I've read a glow plug can stil be down without triggering the lamp circuitry.

The old test for a completely blown glow plug is to measure its resistance - usually measuring open circuit - is this just the same test for one that may be partially working, or is there another (quick and easy) test?

Any help will do.

 

[Parrot of Doom]

If you're going to do one, do them all.

Otherwise, remove the connections from the plugs and measure the resistance. The faulty one will be very different from the rest.

Also check the glow plug relay, as they have fuse blades which are instantly recognisable when melted. The relay is near the +ve battery terminal on the nearside of the engine bay, just next to the firewall.

 

[Bolide]

The easy way is to take the plug off the relay and measure the resistance of the glowplugs there. The relay is on the n/s inner wing. If it's a 250 it'll have a plug with 5 pins, and a 300, 6 as you'd expect. Measure between pin & earth. IIRC they should be about 0.8 Ohm

Nick Froome
www.w124.co.uk

 

[and11]

1 Down, the rest on way!

I believe that if 1 plug is down the rest will soon follow, possably because too much power going to them soon burns them all out?

 

[Parrot of Doom]

I can't imagine that happening unless the design of the relay was poor. So long as the voltage across each plug remains the same, one plug dying should make no difference to the others.

The main reason for replacing all of them is that if one has died, chances are they're all from the same batch, and therefore will all die in short order - from age and use.