Function of glowplugs after starting

Do the glowplugs in a Focus Mk2 1.8 TDCI have any function once the engine is running?

The reason I ask is that recently I had intermittent problems where the engine management light would come on while driving and the engine would lose power, giving very poor acceleration and an eventual top speed of around 50 mph. The first time it happened the light went out and the engine returned to normal before I could find somewhere safe to stop, the times after that were longer.

I plugged in my reader and the only code present each time was for glowplugs open circuit.

They are cheap enough, so I replaced all four and the problem has gone away - for three weeks and a couple of thousand miles so far.

Unless they are used while running, I can understand a fault being shown, but I can't understand why the need to trigger limp-home mode; however, I always thought that they were only needed for starting from cold.

SteveW

Reply to
SteveW
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I have seen this on a Fusion, the plugs are checked roughly every ten minutes and if the readings are off, limp home mode is triggered, I could find nothing wrong with the old ones, but a new set did the trick.

Reply to
Mrcheerful

Fair enough, but why check them once running? I did wonder was it some sort of resistance measurement to read the tip temperature, but as all four are wired in parallel, it'd not be very useful.

SteveW

Reply to
SteveW

I was once told that they had a secondary function to help control emissions after starting but I don't know how true that is.

Reply to
Paul Giverin

Now that sounds possible. Although I'd have thought the tip would remain hot enough once the engine was running. Maybe everything cools a bit much when there is no fuel during deceleration and extra heat is provided ready to aid emissions as soon as you accelerate.

SteveW

Reply to
SteveW

Definitely used to be true, on Peugeot it justr used to be on a timer, but I assume they've got more sophisticated.

Reply to
Duncan Wood

the check is by voltage reading when power applied, why is outside comprehension as it may occur at 60mph or tickover, I cannot see any emission improvement is really possible from a glow plug when everything is hot and rolling along. on the fusion a pattern set of glow plugs are

50 quid, so it is really galling to change working glow plugs just to stop limp home mode kicking in, and that can be dangerous in itself if it happens as you pull into a fast roundabout.
Reply to
Mrcheerful

Post-glow is very common on diesels, to enhance warmup, and cold running characteristics. They will be in many cases checked by the ECU for continuity and operation periodically.

Most DI engines dont actually use the plugs for cold start until below -5 or lower.

On DPF equiped engines, the glow plugs are fired up during regen, so *must* work, otherwise it will fail, the DPF will block and you face a greater problem!!

Tim..

Reply to
Tim..

Vectra Diesel 2 litre - as part of trying to find out why its cold-starting isn't very good - on a warm winter day at 10 degreees C I disconnected all the glow plugs and tried starting it. It did start, but took a few seconds, coughing and splutting badly.

By contrast, starting with the glow plugs connected, at the same temperature it starts on the first compression.

But at about -5 it will fire and die. It takes several tries, each preceeded with a preheat period, before it will fire and continue to run.

So the glow plugs would seem to be essential for reliable starting, and even then don't do a lot for it at proper English winter temperatures. I wonder how they perform in really cold countries?

Reply to
Graham J
[...]

Some diesels need a really good battery and the correct starter motor, in good condition, in order to start reliably in cold conditions. If, for example, a non-OEM starter, or one for a similar petrol car has been fitted in the past, poor cold starting is likely.

Chris

Reply to
Chris Whelan

I understand that a good battery and and starter motor can improve cranking speed, and this will aid starting by spinning the first few compressions more quickly; but the experience I have is that the engine fires, then dies. By that time I've released the ignition key thinking that the engine will run, so I don't see that cranking speed comes into it ...

Reply to
Graham J

The faster the cranking speed the higher the compression temperature generated because there's less time for heat loss to the cylinder walls and chamber. Therefore an engine which appears to fire but then dies at one cranking sped might fire properly at a higher one.

Reply to
Dave Baker

Old NA Land Rover diesels spring to mind.

Reply to
Duncan Wood

more likely that you have leaky spill pipes drawing in air overnight.

Reply to
Mrcheerful
[...]

And a very common problem with old NA Fords.

Chris

Reply to
Chris Whelan

This is the bit that seems daft. I ordered new glow plugs, but they arrived the day we were going to Ireland and with working that day, packing, etc., I didn't have the time to fit them until I got there. Limp home mode was kicking in on and off throughout the journey - and I can't see anything being too cold when doing 65, uphill, towing a trailer, with five people and luggage and after two hours running! Why on earth check them and implement limp home at such a time?

I definitely found that at temperatures above 0° it was very smokey for a few seconds after start-up, so in this case, I think it uses them at a higher temperature. If the glow-plug light is anything to go by, it seems to use them whenever it starts from cold, except possibly at the height of summer!

No DPF on this fortunately.

SteveW

Reply to
SteveW

Why would that be worse at very low temperatures?

Last Saturday (11 Jan) I replaced the spill pipes and T pieces, using parts bought from the Vauxhall dealer. Ran the car for about 5 miles immediately afterwards. Next day it was a real pig to start - needed cranking for 30 seconds - and this at about +8C. Is it likely that there was still air in the spill pipes? Ho far should I expect to drive to completely purge the air?

The old spill pipes were clean and flexible, and showed what looked like a 2012 date code.

Reply to
Graham J

Right, next port of call would be to check the valve clearances for any that are TIGHT cold, and then move onto a cold and hot compression test, whilst you are at it, cranking RPM (250 or better). A cylinder balance test if you are being keen.

Double check the fuel is not running back to the tank overnight.

Reply to
Tim..

Are you sure? My understanding of DPF regen is that extra fuel is injected to burn off the carbon in the filter. This may be done "on the cheap" by using an engines existing injectors or there may be a separate injector in the exhaust system upstream of the filter.

Tim

Reply to
Tim+

one of the other problems they have is leaks at the fuel filter, usually cured by using a genuine filter kit, sometimes by replacing the whole housing.

From the symptoms you describe it sounds like air getting in while it is standing. Which is a very common fault with that vehicle (as a google search would show) My sister has one and I messed about for ages before discovering the spill pipe problem.

Reply to
Mrcheerful

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