New glow plugs needed?

[21TonyK]

I'm assuming that if a diesel is takling up to half a dozen attempts to start when very cold then the glow plugs are a likely issue.

OBD shows no codes and it starts on the button if its above about 8C so I'm think plugs and not a controlelr module that would show a code? (I'm guessing)

Cars on 96K, I think original plugs as no history of them being changed.

[E-bmw]

Frequently a better reader can detect codes that cheaper ones don't.

If you have a multimeter that will read Ohms they are very easy to test.

You just need to go across the electrical connection & the engine to see what the resistance is, they should all be the same and normally around 5 ohms.

Once you have done that, check they get 12 volts when turned on.

[21TonyK]

Cheers. I do have a multimeter, need to do a bit of googling to find out how to use it!

I assume these tests are in situ?, ie top of plug/engine casing?

[zedx19]

On the family a bus, a 1.6HDI Peugeot 5008, a few years back it would take ages to start during cold months, just cranking and cranking before catching. I thought it was the glow plugs and didn't fancy them snapping, so dropped at a garage. They rang and said they'd tested the battery and it looked to be on its way out and they suggested trying that before plugs. New battery on and it started straight away and still does now, even during the -6 temps we had a few weeks back.

Check the battery first as our battery seemed fine, car would unlock, wing mirrors fold out all as normal and I noticed no change in engine turning over like you'd hear with a low battery, but it clearly wasn't providing enough juice to the plugs, even though the glow plug light would go out.

[E-bmw]

Very valid point.

If the battery isn't brilliant the drain caused by turning over a very high compression engine can be significant, especially following putting 4 x 5 ohm shorts from the battery to the glow plugs.

[21TonyK]

Ok, I'll go stick the battery on a trickle charge now and try it first thing in the AM to rule that out first.

Failing that test the plugs and the supply to them, Haynes says 5-7 volts?

[Smint]

An older mechanically injected Diesel needed some warmth from the glow plugs to start smoothly/quickly, not the case with common rail engines, my 20 year old common rail Prado fires up instantly an all cyls long before the glow plugs would have any chance to heat up.

If you have a primer plunger on or near the fuel filter, it would be worth operating said plunger before attempting a cold start, if you have to press several times before the plunger firms up (proving the filter is full of fuel) then you might have an air leak or fuel leaking back into the tank while stopped.
If it fires instantly after priming you'll have an idea where to look.

Last time i tested glow plugs in situ ISTR each plug consumed 12/15 amps whilst operating.

[21TonyK]

^^^ Cheers for the info, its a '14 Mini common rail etc etc

[Richard-D]

If you're able to check the resistance from the top of the glow plug to battery negative this could quickly show your issue. Most engines need the glow plugs disconnecting to make this a valid test. There will be an expected spec for resistance available if you Google it for your engine.

[donkmeister]

Obviously a patch rather than a fix, but can you still add a little petrol to the fuel to ease cold starting* or does that mess sensors up?

( * Even in the winter blend fuel)

[21TonyK]

Ok, so battery on charge for 7 hours. Still took 8 presses of the start button to fire up this morning.

Now testing the resistance of plugs (in situ?)

[Smint]

21TonyK said:

Ok, so battery on charge for 7 hours. Still took 8 presses of the start button to fire up this morning.

Now testing the resistance of plugs (in situ?)

Try priming the fuel system before attempting start tomorrow?

[21TonyK]

Ok, so battery made no difference. And now, using my trusty Radio Shack Mutitester (yes, 1983 Radio Shack as in Tandy) I am getting 4.5(ish) Ohms on all 3 plugs and 0 on the three cables connecting to them from the controller.

So I'm assuming the problem lies elsewhere or its deeper than dodgy plugs.

I do have a note from the previous owner showing they were replaced as was the relay. This shows a date code of 2024 on it so I'm tempted to believe it.

Possibly the whole thing is linked to the EGR which need sorting under recall soon anyway.

Time to put it all back and see if it still starts!

ETA: only one screw left over!

Edited by 21TonyK on Tuesday 28th January 12:46