As the Td4 is a common rail system then how can you have leaking injectors? With the pressures these systems run at then surely the fuel would flood out and fill the bore. This would then make the vehicle impossible to start. The smoke on start up must be another issue or am i missing something here. I thought the Td4 injectors were operated by an electric pulse, so were either open or closed, so if open then it would pour in. Im confused . com

'leaking' .. wear and tear .. faults ..
most often caused by fuel contamination ..
grit/dirt will score the surfaces ..
air or water will prevent lubrication ..

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the presence of diesel bug won't help either

re. diesel bug .. be the slime/jelly-like substance in this sedimenter ..
http://www.landyzone.co.uk/lz/1881953-post2.html

diesel bug and injectors ..
http://www.uniteddiesel.co.uk/tips_docs/Problems with fuel.pdf

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so if a sealing surface don't seal properly .. it will 'leak'
not neccessarily pour in ..

informative animations ..
although presentation is let down by use of computer voice ..
( text to speech probably )

How Bosch Piezoelectric Diesel Injector Works
How Bosch Piezoelectric Diesel Injector Works - YouTube

Diesel Piezo Injector Pulse Anatomy
Diesel Piezo Injector Pulse Anatomy - YouTube

Diesel Piezo Injector Pulse & Pressure
Diesel Piezo Injector Pulse & Pressure - YouTube

Diesel Piezo Injector Voltage & Current
Diesel Piezo Injector Voltage & Current - YouTube

Diesel Common Rail Injection Facts 1
Diesel Common Rail Injection Facts 1 - YouTube

Diesel Piezoelectric Injector Driver Circuit
Diesel Piezoelectric Injector Driver Circuit - YouTube

Diesel Common Rail Injection Facts 2
Diesel Common Rail Injection Facts 2 - YouTube

Diesel Injection Pressure Sensor
Diesel Injection Pressure Sensor - YouTube

Diesel Pressure Sensor Testing
Diesel Pressure Sensor Testing - YouTube

Diesel Fuel Pressure Limiter Operation
Diesel Fuel Pressure Limiter Operation - YouTube

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Diesel Variable Geometry Turbo Introduction
Diesel Variable Geometry Turbo Introduction - YouTube

Diesel Variable Geometry Turbo Facts
Diesel Variable Geometry Turbo Facts - YouTube

Diesel Variable Geometry Turbo Details 1
Diesel Variable Geometry Turbo Details 1 - YouTube

Diesel Variable Geometry Turbo Details 2
Diesel Variable Geometry Turbo Details 2 - YouTube

Diesel Variable Geometry Turbo Failures
Diesel Variable Geometry Turbo Failures - YouTube

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and btw: ..
a.f.a.i.k. .. the maf sensor works with .. or .. is one thing that determines ..
injector pulse width .. .. i.e. how long the injector is 'open' ..
( at least that's the conclusion i came to after reading some tech. article ..
( a google book on tuning injection systems ..
( i could be wrong ..

Very simply, the internal seal fails it allow fuel to return via the return pipes that plug into the top of the injectors. As you are cranking you need if memory serves 6000 psi, if the rail does not reach this pressure then it will not start. Once it fires the pressure increases to 28000 psi and at this point it does not matter if the injector is leaking it will run fine till you switch off and than it will not start again, that is why in a emergency if you start it with easy start it will get you home.

Wot he said^^^^

Thanks for the replies, now i understand it better.