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Cold starting of direct injected diesel engines.

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Cold starting of direct injected diesel engines.

Postby winterheating » Sun Dec 18, 2011 2:41 am

When temps start to drop, any small problems will start to show.

3 things only are needed for a direct injected diesel to fire :!:

1. Air

If timing is out at cranking, it could not allow enough air into combustion chamber, could also be valve problems if they are not opening enough but still in time.

Air filter could be blocked or water logged.



2. Fuel

For fuel to be fired it needs to have no air bubbles in the lines and pump, to allow high enough fuel pressure to build up at the slow cranking speed.

The pump has to be turning quick enough to create the required fuel pressure at cranking, which could be restricted due to voltage, tight starter, tight engine due to oil thickness, either wrong or old engine oil.

The fuel pump requires a minimum cranking voltage to operate also otherwise it will never fire. Again could be battery, connections, starter pulling too much for whatever reason.

The fuel also needs to atomise fully to ignite, it may not atomise if injectors are worn, or low pressure due to restrictions in low pressure side like the fuel filter, or air.
Or just worn pump.
.

3. Heat

The heat from a direct injected diesel engine is produced only by compression of air in the cylinders.

This can only be done if the right amount of air is compressed and quick enough.
If you turn the engine by hand you will not raise the compression/heat anywhere near enough for ignition.

If an engine is turned too slowly the air is not compressed quick enough to create enough heat, it may be quick enough to still fire the fuel so you would get unburnt diesel smoke from exhaust.

If an engine has a cylinder or 2 with lower compression then if it were low enough to stop the ignition, you would get a miss fire when started.

also if glow plugs were needed to give extra heat then again you would get a misfire once started At the cylinder with faulty glow plug.

If an engines compression was dropped from 20 to 12 bar if it had fuel firing still and enough air the compressed air at that level is still enough to create enough heat even in minus conditions.
If the engines compression dropped further it would would be uneven wear or damage so again you would get a misfire when eventually fired.




Engine oil thickens, you could also have the incorrect oil in so will be far to thick, restricting cranking speed.

A low charged battery will drop even further in the cold also further reducing engine cranking speed.

You can not tell a cranking speed by just listening to the engine turning, or the actual cranking voltage.
the cranking voltage will need to be high enough to actually energise the fuel pump


So cranking speed, and voltage are needed to create enough heat from compression and fuel to injected and atomised.
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Re: Cold staring direct injected diesel engines.

Postby stevenstead » Sun Dec 18, 2011 10:03 am

Very interesting. Thanks!

This explains my poor cold starts...

If you turn the engine by hand you will not raise the compression/heat anywhere near enough for ignition.

If an engine is turned too slowly the air is not compressed quick enough to create enough heat, it may be quick enough to still fire the fuel so you would get unburnt diesel smoke from exhaust.


Always turns rather sluggishly on a cold morning and seems to 'catch' after turning the engine twice for 5 seconds. By 'catch' I mean the engine seems to have fired but it's turning over very slowly and seems to be started but you have to press the accelerator a few times to get up to 850rpm idle speed.

It was very much improved when I repaired the glowplug fuse wire and took out a shorting plug to stop it blowing again, but this winter it seems to be back to old tricks again.

The neighbours love my smoke screen trick in a morning. You see the road and my van.......now you don't!! 8)
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Re: Cold staring direct injected diesel engines.

Postby blue estate » Sun Dec 18, 2011 10:20 am

Just to add another thing if your battery is flat due to the cold aswell DON'T BUMP START :!: as the little problems listed in winterheating's post will be the last of your worries :wink:
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Re: Cold staring direct injected diesel engines.

Postby mikesenior » Sun Dec 18, 2011 5:13 pm

Nice post Winterheating

after reading it I checked my air filter and found it to be sopping wet, then found the previous posts about how water gets in.

I've probably used a not very technical temporary fix, by leaving it on the radiator at home to dry out, took at a bit of care to ensure the filter cover re-seated correctly when I put it back in.

Hoping it starts a litle bit easier tomorrow

thanks
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Re: Cold staring direct injected diesel engines.

Postby winterheating » Sun Dec 18, 2011 5:25 pm

Easiest is to try and get top cover rear lugs located with the cover up at 45degrees or as hi as possible, shove it back so it's located right, this will give enough space to not move the outer filter seal then can just push the whole thing down and will be sealed nice and tight.
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Re: Cold staring direct injected diesel engines.

Postby wexican » Tue Dec 20, 2011 12:43 am

Thanks
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Re: Cold staring direct injected diesel engines.

Postby winterheating » Tue Dec 20, 2011 1:09 am

Let me know if there's anything to add or change and I'll edit first post.
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Re: Cold starting of direct injected diesel engines.

Postby Jezclayton » Wed Jan 11, 2012 4:00 am

I guess the other thing to check is that the fuel filter isn't full of water?
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Re: Cold starting of direct injected diesel engines.

Postby evilgoat » Sat Jan 21, 2012 3:38 pm

If you've been using easy start / start yer ba*tard into the intake it will clog the air filter over time too.
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Re: Cold starting of direct injected diesel engines.

Postby ake » Sat Jan 21, 2012 5:08 pm

evilgoat wrote:If you've been using easy start / start yer ba*tard into the intake it will clog the air filter over time too.

Clogging the air filter will be the last of your worries using that shite. It does major damage. All Transits should start with out any assistance even at -18 c like we had last winter
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Re: Cold starting of direct injected diesel engines.

Postby Richach » Mon Jan 23, 2012 4:21 pm

winterheating wrote:When temps start to drop, any small problems will start to show.

3 things only are needed for a direct injected diesel to fire :!:

1. Air

If timing is out at cranking, it could not allow enough air into combustion chamber, could also be valve problems if they are not opening enough but still in time.

Air filter could be blocked or water logged.



2. Fuel

For fuel to be fired it needs to have no air bubbles in the lines and pump, to allow high enough fuel pressure to build up at the slow cranking speed.

The pump has to be turning quick enough to create the required fuel pressure at cranking, which could be restricted due to voltage, tight starter, tight engine due to oil thickness, either wrong or old engine oil.

The fuel pump requires a minimum cranking voltage to operate also otherwise it will never fire. Again could be battery, connections, starter pulling too much for whatever reason.

The fuel also needs to atomise fully to ignite, it may not atomise if injectors are worn, or low pressure due to restrictions in low pressure side like the fuel filter, or air.
Or just worn pump.
.

3. Heat

The heat from a direct injected diesel engine is produced only by compression of air in the cylinders.

This can only be done if the right amount of air is compressed and quick enough.
If you turn the engine by hand you will not raise the compression/heat anywhere near enough for ignition.

If an engine is turned too slowly the air is not compressed quick enough to create enough heat, it may be quick enough to still fire the fuel so you would get unburnt diesel smoke from exhaust.

If an engine has a cylinder or 2 with lower compression then if it were low enough to stop the ignition, you would get a miss fire when started.

also if glow plugs were needed to give extra heat then again you would get a misfire once started At the cylinder with faulty glow plug.

If an engines compression was dropped from 20 to 12 bar if it had fuel firing still and enough air the compressed air at that level is still enough to create enough heat even in minus conditions.
If the engines compression dropped further it would would be uneven wear or damage so again you would get a misfire when eventually fired.




Engine oil thickens, you could also have the incorrect oil in so will be far to thick, restricting cranking speed.

A low charged battery will drop even further in the cold also further reducing engine cranking speed.

You can not tell a cranking speed by just listening to the engine turning, or the actual cranking voltage.
the cranking voltage will need to be high enough to actually energise the fuel pump


So cranking speed, and voltage are needed to create enough heat from compression and fuel to injected and atomised.


Hello

Yeap i have problems starting mine, it fires but with plenty of smoke. Not sure what to try next

Had a 120000 major service including air filter (dry) 3 weeks ago
Water pump was dry and changed at same time
2 weeks later EGR valve
Last week not firing so fuel filter housing and filter changed, no air in system as of friday unless still taking in air.

To be fair it runs really well when its warmed up

Still have smoke and firing at 2nd or third crank is starts slowly and then eventually wakes up. Glow plugs disconected last week.

Question is any further damage being caused if issue not addressed and also where do i take it to get diagnosis and repair as the local "dealer" dont understand my language they just nods and ask for £300 a time without fixing problem.
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Re: Cold starting of direct injected diesel engines.

Postby winterheating » Wed Feb 08, 2012 7:23 pm

Also just to add other thaN A Tight starter, could also have a tight or seized altenator or water pump, causing low cranking speeds and low cranking voltage.

Also theres Something else someone mentioned the other day but cant remember....
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Re: Cold starting of direct injected diesel engines.

Postby whitemice » Wed Feb 08, 2012 7:32 pm

winterheating wrote:Also just to add other thaN A Tight starter, could also have a tight or seized altenator or water pump, causing low cranking speeds and low cranking voltage.

Also theres Something else someone mentioned the other day but cant remember....


Was it the timing chain issues here?
viewtopic.php?f=5&t=103351&p=874337&hilit=timing+chain#p874337
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Re: Cold starting of direct injected diesel engines.

Postby winterheating » Wed Feb 08, 2012 7:40 pm

Err might have been yeah.

As the timing can jump one or two teeth, because of faulty timing chain tensioner,
cause slight damage to cam carrier or snap one or 2 bolts so that the first few valves do not lift enough, causing starting problems but seem to run ok once started.
Not as common to fail exactly like this but have seen it a few times.
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Re: Cold starting of direct injected diesel engines.

Postby whitemice » Wed Feb 08, 2012 7:50 pm

My first thought is timing chain tensioner (was what caused mine to do this), when it fires does it sound really rattly in the second or so before it stalls If so then tensioner is a definate culprit (when chain is slack pump timing is out to crank timing, causing ECU to kill engine). Also when did it last have an oil change

Andy
......................................

As Andy said in that link the above is an issue also.
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