2 litre HDI smoking when cold

[Harlequin]

Heya - got a xsara HDi - smokes like a trooper on startup and clattery , quickly quietens down.

now - what could the start up smoke be - it smells of unburnt diesel , which leads me to injectors , fuel pump advance or post heating not working properpy.

maybe.

any idea`s? have a running lexia screenshot if it helps?

[chris222333]

If it takes ages to start then maybe compression if high miles. If not suspect glow plugs/fuel system. A good way to test is to unplug the coolant temp sensor turn the key so the glow plugs cycle 2 or 3 times. Plug the sensor back in then try and start. If the smoke has gone its to do with not enough heat in the cylinder at startup. Bear in mind it is very cold at the moment. Watch some youtube videos of cold start diesels in cold climates I wouldn't worry lol

[white exec]

I remain confused by this. Several folk have stated that HDi glowplugs don't operate unless temperatures are Arctic; others have said they play no part in starting....

What really is the case on these engines?

[Harlequin]

which is the coolant temp sensor and where is it located?

[GiveMeABreak]

I remain confused by this. Several folk have stated that HDi glowplugs don't operate unless temperatures are Arctic; others have said they play no part in starting....
What really is the case on these engines?

Chris - Apologies in advance if you know all this - I’ve summarised some info here from various docs - this is for Delphi Injection, but is the same for Bosch. This relates to my C5 X7 2.0 HDi, but I'm sure is relevant to other HDis.

Pre-heater Plugs
The plugs enable a rapid rise in temp. inside the combustion chamber during starting and cold-running phases. They are also used for de-pollution by reducing the NOx and Soot. They have 4 modes of use: Pre-heating, Pre-heating under Starter, Postheating & Postheating for Regeneration.

These modes are controlled using the pre-heating control unit on the orders of the engine ECU.

Pre-postheating
The pre-heating starts as soon as the ignition key is turned on. The pre-heating and postheating times are determined by the engine ECU as a function of the engine coolant temp., air temp, atmospheric pressure as well as the engine operating phase that is in use (e.g. engine speed and load too high). Pre-heating times vary according to coolant temp and the temp. of inducted air.

Postheating
The postheating phase starts as soon as the pre-heating phase is finished. The length of activation depends on the engine coolant temp, air density as well as qty. of fuel injected.
Postheating stops when:
The postheating times are exceeded, the ideal value of the coolant temp has been reached or when the value for the air inlet temp. is wrong or the value for the engine speed and load is too high.

Postheating is used for limiting emissions of hydrocarbons and Carbon Monoxide. It is used for loading the engine in order to bring the catalytic converter and / or the particle filter up to optimal operating temperature as soon as possible. Actions of postheating include prolonging the operation of the pre-heater plugs after the starting phase, reducing the emission of pollutants in the first few minutes after starting and reducing blue fumes especially at altitude.

Regeneration
When a regeneration of the DPF is in progress, the BSI may ask the Engine Management ECU to operate the pre-heater plugs so as to ‘load’ the engine (to increase electrical consumption in order to augment the engine temperature needed to regenerate the DPF ). Then plugs are operated for 1 second max. and depends upon engine speed and fuel flow (risk of overheating and knock).

There are tables that reference the pre-heating times according to the coolant temperature against the atmospheric pressure in hectoPascals - etc., but you get the drift...

What is interesting though is that apart from this, during a regeneration of the DPF, by increasing the resistant torque of the alternator, the torque of the combustion engine increases as does the temp. of the engine. This load acquiring allows for a faster increase in the engine temp., in order to improve the regeneration of the DPF. The BSI can command the following electrical equipment to be activated in the following order: 0 - No Load, 1 - Activates Heated Rear Screen, 2 - activates the fan assembly (low speed), 3 - activates the fan assembly at medium speed and 4 - activates the pre-heat glow plugs. So I've now learnt another thing today!

[white exec]

Thanks, Marc, for the excellent detail. I've learned a few things about regeneration techniques here too!

There have been several suggestions in recent posts that poor/smoky starting, and in cold weather, on HDi will have nothing to do with the functioning, or not, of glowplugs - and hence my request for some authoritative clarification. It has also been stated that GPs on HDi's do not function until the temperature has dropped to -5degC.

My understanding is that all current diesels will be reluctant to start in cold weather, unless, at the very least, some effective preheating is provided. Heating by cranking compression alone is not sufficient for a quick and reasonably clean start, because of the heat losses into the cylinder walls, pistons and head. Very high injection pressures will help, but even the best atomised diesel fuel will tend to re-condense in cold surroundings.

If there are examples of our diesel cars being designed otherwise, then hopefully someone will post details.

Thanks again, Marc, for all that detail.

[GiveMeABreak]

No problems Chris, I thought it might help clarify some of those 'glow plug' issues. Here are a couple of tables one for the post-heating and the second is for regeneration - when the 1 second kicks in:

The following can interrupt post-heating:
Coolant temp above 50°C
Injected fuel flow exceeding 30mm³ (between 1200 & 1500 rpm)
Injected fuel flow exceeding 10mm³ (2500 rpm)
Injected fuel flow exceeding 5mm³ (3300 rpm)
Engine speed above 3500 rpm

In the table below, Column 'B' represents the coolant temperature and 'A' the number of seconds they are activated for depending on the atmospheric pressure in hectoPascals (hPa).


Regeneration - Glow Plug activation (duration of 1 second) v Engine speed

[white exec]

Marc,
At what (coolant) temperature does pre-heating not take place?
C.

[Harlequin]

how can I trick the glow plugs to stay on as if it was -20?

[white exec]

First check whether they are coming on or not - test meter or test lamp on one of the GP terminals.

[GiveMeABreak]

Marc,
At what (coolant) temperature does pre-heating not take place?
C.

Sorry Chris, I forgot to put a legend on the table - just gone in and edited my previous post. So according to the first table, pre-heating always takes place to start with once the ignition is switched on for at least 10 seconds, unless coolant temp is at least 60 °C when it decreases to 7.5 seconds or 5 seconds at 80 °C.

So I can't see anywhere that they are not active unless hotter than 80 °C!

[white exec]

OK, Marc, I'm with it. The time quoted is total time, pre- plus post-heat, at the temperatures stated.

So, unless engine is hot (80degC+), glow-plugs will always operate when starting.

This confirms, then, that proper GP operation is required under normal 'first-thing' starting conditions.
Just a bit worrying to find suggestions to the contrary, or recommendations to forget the GPs, and replace starter motors!

[ekjdm14]

I'm surprised this hasn't been "put to bed" conclusively. I've read similar statements and always thought it weird. Perhaps it's because the actual GP light doesn't light until the temperatures are below freezing, confusing people into thinking the plugs aren't working when if fact they are, I think all the light is on these cars is an indicator when the engine is not in a condition to start reliably.

I am tempted to do a quick 'n' dirty test on our 1.4HDi with a test lamp & see what the plugs are doing in various temperatures.

[jgra1]

interesting marc..thanks for asking chris

having just rebuilt an older hdi, I was suprised (nothing about this van will shock me now lol) - to find all four plugs were duffers!!
it started well enough in warmer weather ?10c or so

[white exec]

The compression stroke on a warmed up engine will raise the air temp in the cylinder to 600degC or so, which is what ignites the atomised fuel when it is injected. Cranking does this much slower, and the temp rise is less.

On a cold engine, much of the cranking heat is lost to the metalwork, and so starting a diesel without working glowplugs on a very cold morning can require lots of cranking, to generate enough heat to begin to ignite the fuel. On some cars, starting is so bad it does't happen, battery voltage drops, starter motor slows, heat generated is even less - and the result is a flattened battery. A rescue jump-start will often get things started, stutteringly, simply because it spins the starter motor more quickly.

All this can be avoided by having a set of properly working glowplugs, and decent battery connections. Beware those selling starter motors! These can die, but not often. They are certainly not the first thing to jump on.

Sorry to have to write all this; I too thought it had been put to bed. Never assume!
Thanks to everyone who has picked this up and pitched in with good information.