Starting a diesel Bongo - avoiding smoke / misfire

[bigdaddycain]

Im no engineer mike,but it sounds like you just caught it "on the hop" as it were. My procedure when very cold i.e "a window scraper", is to let the glow plugs do TWO cycles, wait for orange light to extinguish, wait for click, then a short turn of the key, with no throttle, then bob's ya uncle's mother!
Its the same principle as on some HGV'S where on a cold morning you hold the ignition between point one and two for continuous glow plug activation (about 10 seconds)

Otherwise mike, just wait for the click,if it misses on start up,chances are the smoke is just unburnt fuel exiting the exhaust...nowt to worry about mate.

[mikeonb4c]

Absolutely bigdaddy, unless I'm a monkeys uncle (hmmmm could be) Mango has a kick like a mule when you get her started - nothing wrong with HER glowplugs (I hope)

[Steve from Carlisle]

Mike / all

I'm not qualified to say either... I've always been led to belive damage may be caused to the various pipes attached to the engine, probably by vibes. I always feel better in the Bongo giving it a few revs, easing off to engage D then driving away ASAP. The benefits of this routine might just be in my head but it seems better than just letting it rattle and chug till it warms up. I sometimes think there are more 'old coach drivers tales' than 'old wives tales' . But hey sometimes there worth a go!!!

Steve

[mikeonb4c]

Its interesting Steve. The thought I had this morning was whether putting your foot down if it was misfiring on startup (as we tend to do when a difficult petrol engine finally fires up) might actually prolong the misfiring and smoke unnecessarily and - if the plugs (or power to them) are a bit weak - then it might quench them a bit, compounding the problem. But diesels must gie their mountings a lot more grief than petrol. When I switch Mangos engine off, there's a healthy shudder put out as the engine stops (big mass, high compression I guess).

[Steve from Carlisle]

Hmmm.

From time to time I wish I had a better understood of the mechanical workings of things. My day job is in IT and I drive coaches (as my other half puts it) as a profitable hobby. I don't think a few revs would worsen the problem as the plugs heat the air in the cylinders and surely more combustion cycles would create more heat that electric glowplugs?

On an aside I have a Peugeot 307. It has a glowplug light, yet in 40K miles I have only seen it on about 3 times. Anyone any idea why?

Steve

[francophile1947]

I agree with the revving Steve.
Sounds like glow plug light is faulty, as every diesel I've had lights the light, even if you don't need the glow plugs. I've got a Fiat Doblo with the 1.9 JTD engine and I never wait - it just starts like a petrol, so does my neighbours 2.2 Picasso.

[grumpo]

Comparing different diesal engines is similar to comparing oranges to
bananas. Many modern engines, including common rail engines, are
usually direct injection types, whereas the Bongo WL/T engine is an
indirect injection type which starts the combustion process in a small
chamber above the main cylinder.

Indirect injection engines are designed to improve starting and run
smoother while below normal running temperature. The principle was
first introduced for cars by Mercedes in the early 80's to justify the
inclusion in their range of cars, other manufacturers followed suit.

Direct injection engines are usually a lot noisier but slightly more
efficient, the ford transit engine is an excellent example of this where
fuel consumption is far more important than driver comfort.

Common rail engines reduce the noise of direct injection engines by
electonically controlling the injection timing and fuel quantity, as well
as providing much higher injection pressures. Common rail principles
now make pre-combustion virtually obsolete.

The problem with indirect injection is that the pre-combustion chamber
can get far hotter than the main combustion chamber and the design
of the water jacket surrounding the pre-combustion chamber is extremely
important, one of the reasons the Bongo can destroy cylinder heads
through lack of coolant, due to air in the cylinder head.

[Bongo and Tonic]

I too experience white smoke and lumpy running. It starts OK, idles OK for a few seconds, then starts misfiring and lots of white smoke.
Might give the advice above a try.

[mikeonb4c]

Phew - grumpo knows his stuff. Could glowplugs get quenched by pushing accelerator down hard in response to a lumpy start when cold grumpo?

[dandywarhol]

Phew - grumpo knows his stuff. Could glowplugs get quenched by pushing accelerator down hard in response to a lumpy start when cold grumpo?

Yes!

Excellent write up grumps - I've said before - you should be writing workshop manuals - would certainly make Haynes get their act together to tidy up their "mistruths"

[francophile1947]

Phew - grumpo knows his stuff. Could glowplugs get quenched by pushing accelerator down hard in response to a lumpy start when cold grumpo?

Why push it down hard - a quick blip seems to sort mine.

[grumpo]

Thank you Dandy, you have inspired me, perhaps I should
have gone to bed early last night !!!.

Pure white smoke from the exhaust is condensed water
vapour. All engines burning hydrocarbon fuels produce
water vapour all the time due to the hydrogen content.

The main elements of diesal fuel are approximately:

Carbon 87 %
Hydrogen 10.5 %
Sulpher 0.05 % or less
Nitrogen 1 %
Oxygen 1 %

In the burning process, 1 atom of carbon combines with
2 atoms of oxygen and produces CO2 ( carbon dioxide ).

2 atoms of hydrogen combine with 1 atom of oxygen and
produces H2O ( water ).

The sulpher combines to sulpher dioxide ( sulphuric acid )
and nitrogen combines to nitrous oxide.

Due to the high combustion temperatures, the water is in
the form of steam, steam is invisable, you can only see
it when it condenses into water vapour. On a warm day
with low humidity, the steam is absorbed into the
atmosphere and so never becomes visable, on a cold day
the steam condenses immediately it leaves the exhaust
system and becomes visable as water vapour until such
time as the exhaust temperature is high enough to stop
condensation and the water vapour disperses before it
becomes visable.

So, why would an engine start normally, and then after
a short time start to run "lumpy" and produce excess
amounts of water vapour from the exhaust pipe ?.

Excess water vapour normally results from water in the
exhaust system evaporating, when the engine is first
started, however, this should not effect the engine
and leads one to suspect that a small amount of coolant
water is leaking into a cylinder overnight. When the
engine fires, the water will evaporate to steam and so
quench the combustion process until all the water has
cleared from the cylinder.

Given a good battery, and all else is in good condition,
the Bongo will normally start with 3 active glow plugs.
The engine will run "lumpy" for a few seconds until
the deprived cylinder gets up to a reasonable combustion
temperature. If you only have 2 active glow plugs, the
engine probably will not start in coldish conditions
but you can hear it knocking in it's attempts to achieve
power.

If there is a defective glow plug and the engine starts,
then it would help to depress the accelerator very
slightly, any more than this will only increase the
vibration to a point where you may cause damage.

All the above of course is pure conjecture, and may be
a load of garbage, if so, then I apologise for that.

[mikeonb4c]

Grumpo wrote:

Given a good battery, and all else is in good condition,
the Bongo will normally start with 3 active glow plugs.
The engine will run "lumpy" for a few seconds until
the deprived cylinder gets up to a reasonable combustion
temperature. If you only have 2 active glow plugs, the
engine probably will not start in coldish conditions
but you can hear it knocking in it's attempts to achieve
power.

This to me is the interesting bit. In answer to francos question, its not that you SHOULD press down on the accelerator, its that a lot of peoples instinct is (wrongly) to press down in order to get the engine to pick up. But if the glow is a bit weak, squirting a load of cold diesel in the chamber will probably just prevent its attempt to glow. All this becomes more critical when one or two plugs are getting a little tired, but the situation can be ameliorated by intelligent and informed starting technique.


Mike

PS - There is a similar example of 'pilot reaction' in flying, that has to be trained out of people. If you stall an aircraft (let it slow up too much so it starts falling to ground) near the ground then, scary though it is, you have to resist the temptation to pull back on the stick in an attempt to make the plane fly up back into the sky. It has to be allowed to regain flying spead by letting it dive towards the ground, before you can pull back on the joystick to get back to a level or climbing attitude.

[carina]

I have also experienced problems with starting my bongo in the mornings this past winter. last year i had no problems and she always used to start first time with no smoke or judders. now she makes a lot of fuss starting in the mornings and it normally takes 3 goes at turning her on and waiting for the light to go off before she starts. This is followed by quite a bit of shuddering and LOTS of smoke which clears after about 10-15 secs. Later in the day i have no such problems starting her! it seems to be only when she's cold. What i'm wondering is why she's started doing this now (last winter '05/'06 there was no such problem) and if there's an underlying problem that can be fixed??

[dandywarhol]

Duff glow plug/s Carina - plenty bumf in the search facility