300Tdi glow plug operation

With most of the modern vehicles that have a glow plug warning lamp it is usually just a rough guide and the warning lamp does not control the relay for the glow plugs. If you watch the other warning lamps ( charge lamp and oil ) carefully you will see them suddenly get a bit brighter as the relay powers off and usually this is quite some time after the glow plugs warning lamp goes off. Just leave it for a while after the warning lamp goes off and you will see. I never wait for the glow plugs at all on mine as it always starts instantly without, which suggests to me that you may have a fuel or compression problem.

Martin

Plug timing, certainly on the modern diesels, is based on engine block temperature, and like Martin says, is not measured by the glowplug light. The plugs on our Renault used to stay lit for a few seconds after the engine was firing to cut down on smoke I think the garage said when we had some gyp.

Stick a voltmeter on the glowplug rail and see what sort of timing you get at the moment.

I notice, again admittedly, on the Renault that only one buggered plug was enough to give the symptoms you are having too.

Steve

I think the problem I have is down to running 50:50 veg oil:diesel rather than anything else ~ or at least I hope so :-)

I'll check the supply to the plugs with a voltmeter in the morning and see how long they're on for.

I'm not sure a 300Tdi qualifies as a "modern diesel" :-) and there's no sign of any temperature sensor in the wiring diagram for the glow plugs.

I'll get the voltmeter out in the morning and see how long they're energised for.

As a general rule anything from 0.2 to 1.5 Ohms dependant on application. I no longer have a spec book available to me so I can't be more specific.

On or around Thu, 25 Oct 2007 20:08:19 GMT, SteveG enlightened us thusly:

guranteed you'll find at least 2 plugs not working.

the TDi, in good nick on a warm day, will fire up without any.

On or around Fri, 26 Oct 2007 17:58:49 +1300, EMB enlightened us thusly:

note that I've seen one at least that measured OK on an ohmeter but was glowing otherwise than at the tip... needless to say, it's only the tip that's in the combustion space.

Mine worked fine until three were not working. Even with three 'broken' plugs it still started, just a bit sluggish when cold. It never took more than two tries.

With four new plugs in it doesn't seem to matter how cold it is, though I _do_ let the plugs warm up before turning the key. And yes, hte plugs stay on a bit longer than when the light goes out.

Yep, only true test is to remove them and apply 12V to check firstly that the tip glows, and secondly that it glows in the time specified (anywhere from about 4 secs to 20 secs depending on the type of glow plug).

I was going to ask if you were running on veg oil but forgot to. Maybe a combination of too much veg in the mix, one or more knackered glow plugs, dirty filters and a tired engine.

Martin

The temperatures we've had in the last week havent been cold enough to require the glow plugs- its a DI engine- look else where for your problem.

tim. .

It'll most likely be the veg oil unless he's running on homeopathic dilution levels, I know that when I was on 100% it only took the onset of a warm-ish autumn several years ago for the truck to struggle to start, and this was a machine that on diesel would fire on the first turn even when covered in ice. Once back to diesel, the truck was back to firing up at the slightest provocation.

I got the trusty voltmeter out yesterday morning to see how long the glow plugs are being energised for ~ after several activations of the ignition switch I timed an average of 7 seconds. I did this after having already started the engine which, oddly enough, fired first flick of the switch ~ much warmer morning?

It the glow time first activation of the key with a stone cold engine that really matters for checking the glow activation time.

Quite likely.

Looks like a job for first thing tomorrow then ... if it's not raining :-)