Diesel Diagnostics

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Leak off testing #

Posted by Peter Keverne on February 20, 2015, 2:31 pm

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hi
looking for some guidance as regards leak back testing.
How much leak back is good/bad running/cranking?
Would new injectors have no or little leak back?
Should age of injectors be taken into account?
How much variance between injectors is good/bad?
Is 10% or less good?
Should we expect no leak back?
Pointers as to good bad and any further reading etc. most welcome.

peter

Re: Leak off testing

Posted by Shane gray <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3442' width='330' height='300' border=0 style='border:none;'> on February 23, 2015, 4:38 pm, in reply to "Leak off testing"
Shane Gray

Peter,
You should always have some leak off as this is what lubricates the top of the injectors. I always look at about 30% difference either way in one injector compared to others. Remember you can have excessive and not enough leak off.
Shane

Re: Leak off testing

Posted by Peter Keverne <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2835' width='330' height='300' border=0 style='border:none;'> on February 23, 2015, 6:31 pm, in reply to "Re: Leak off testing"
Peter Keverne

hi Shane

thanks for the reply, that is a really good point regarding not enough leak off and one I will take on board when leak back testing in the future. The 30% figure is that from bosch Delphi, etc.?

thanks once again
peter

Re: Leak off testing

Posted by Andy Mason <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2936' width='330' height='300' border=0 style='border:none;'> on February 24, 2015, 1:04 pm, in reply to "Re: Leak off testing"

Different systems will give different results.
A Bosch system should be no more than 35ml after 3 minutes, Delphi and most of the other systems 25ml after 2 minutes.
As said , no leak back also shows a fault.
As far as comparing results, its mainly common sense, if you work on percentages, it all depends on how big the bottles are.
Bosch injectors with excessive leak back will normally be hard to start, Delphi only normally play up when under load.
HTH, Andy

Re: Leak off testing

Posted by Peter Keverne <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2835' width='330' height='300' border=0 style='border:none;'> on February 25, 2015, 10:42 am, in reply to "Re: Leak off testing"
Peter Keverne

hi Andy
thanks very much for that information and has made the leak back testing a lot more precise as to fail and pass injectors.

thanks once again

peter

Re: Leak off testing

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on February 25, 2015, 7:41 pm, in reply to "Re: Leak off testing"
Mark Carter

Watch out if using those figures as different systems from the same manufacturer will give completely different results.

Also the returned fuel is doing a lot more than just lubricating the injector.

Neither of the above is meant as a snub of earlier posts, I just don't want you basing a pass/fail criteria solely on the above.

Mark

Modern cars, Its all wizardry and witchcraft

Re: Leak off testing

Posted by Peter Keverne <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2835' width='330' height='300' border=0 style='border:none;'> on February 26, 2015, 7:33 am, in reply to "Re: Leak off testing"
Peter Keverne

hi mark
I'm sure no one will be offended at your comments, and I for one am grateful for any information that widens my understanding and depth of knowledge, would you be kind enough to expand on "lubricating the injector" or direct me to suitable material to read etc.

thanks once again

peter

Re: Leak off testing

Posted by Tommy Forrest <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1706' width='330' height='300' border=0 style='border:none;'> on February 26, 2015, 10:06 am, in reply to "Re: Leak off testing"
Thomas Forrest

Hi Peter

I might be wrong and hopefully Mark can correct me if I am but as far as I am aware the leak off is the fuel that is returned when the solenoid is activated. This creates an imbalance in pressure above and below the injector nozzle which allows the injector to open.

Tommy

Re: Leak off testing

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on February 26, 2015, 4:13 pm, in reply to "Re: Leak off testing"

>>> would you be kind enough to expand on "lubricating the injector" <<<

The Injector is a mechanical component that has moving parts so it needs lubricating just like any other component.

>>> or direct me to suitable material to read etc.<<<

The series of Bosch Yellow jackets are a very good source of info.

The total fuel volume delivered to an injector has three main functions, 1) to supply the engine with the correct fuel delivery for the current operating conditions, 2) to lubricate the injector, 3) to cool the injector (via throughput)

The return fuel is the fuel that has completed functions 2 & 3.

On a Bosch CR system some of the return fuel you see in the leak off bottles will be the venting of the control chamber (as mentioned above by Tommy)

This is a integral part of the injector operation.

Regards
Mark

Modern cars, Its all wizardry and witchcraft

Re: Leak off testing

Posted by Peter Keverne <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2835' width='330' height='300' border=0 style='border:none;'> on February 27, 2015, 8:32 am, in reply to "Re: Leak off testing"
Peter Keverne

hi mark

thanks for that information, most welcome and has given me a better understanding of leak off testing.
Have ordered diesel fuel injection system common rail by Bosch.

thanks once again

peter

Re: Leak off testing

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on February 27, 2015, 11:27 am, in reply to "Re: Leak off testing"

You are welcome, depending on where you are in the country, Bosch run courses on different diesel systems.

The CR one is called VSD 15

if you are in the SW of England you may be un-lucky enough to get me as the Instructor

Mark

Modern cars, Its all wizardry and witchcraft

Re: Leak off testing

Posted by Tommy Forrest <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1706' width='330' height='300' border=0 style='border:none;'> on February 27, 2015, 4:14 pm, in reply to "Re: Leak off testing"
Thomas Forrest

Peter, I was recently on the Bosch Common Rail course and have to say it was well worth it, although I am still certainly not an expert I did learn a lot of new stuff on the course and would recommend it for anyone that needs more confidence and understanding of Common Rail systems.

Tommy

Re: Leak off testing

Posted by Jarred Toms <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3794' width='330' height='300' border=0 style='border:none;'> on February 27, 2015, 7:31 pm, in reply to "Re: Leak off testing"
Jarred Toms

Where are the courses held in the south west?

Re: Leak off testing

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on February 27, 2015, 9:52 pm, in reply to "Re: Leak off testing"
Mark Carter

The next VSD 15 course I'm delivering in the SW is on the 8th/9th of April at Newton Abbot, Devon.

Let me know if you are interested and I will pass on the contact details to you.

Mark

Modern cars, Its all wizardry and witchcraft

Re: Leak off testing

Posted by David Evason <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3433' width='330' height='300' border=0 style='border:none;'> on February 28, 2015, 10:02 pm, in reply to "Re: Leak off testing"
David Evason

Hi Peter,
Would you mind telling me where you ordered the book from as I too would like to purchase it.
Thanks,
Dave

Re: Leak off testing

Posted by Peter Keverne <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2835' width='330' height='300' border=0 style='border:none;'> on March 2, 2015, 11:35 am, in reply to "Re: Leak off testing"
Peter Keverne

hi david

Quite a few places stock them teeside autotech also amazon bently publishing (usa)

hi mark
working area is south cumbria,just a bit to far for me newton abbot (330miles)will keep eye out for course a bit nearer.Do they have courses over the net bit like scanner danner?

thanks once again

peter

Re: Leak off testing

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on March 2, 2015, 4:06 pm, in reply to "Re: Leak off testing"
Mark Carter

Yes 330 miles is a trek, albeit people have come from further afield in the past.

No Sir, Bosch do not do any "E" learning at present, a lot of the courses have a large practical element to them that would not work via an on-line delivery.

Regards
Mark

Modern cars, Its all wizardry and witchcraft

Re: Leak off testing #

Posted by Jon Morgan <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3190' width='330' height='300' border=0 style='border:none;'> on March 2, 2015, 6:38 pm, in reply to "Leak off testing #"
Jon Morgan

If Marks running the course it'll be worth the journey.

A talented instructor who gets the subjects across well.

Re: Leak off testing #

Posted by Matt Seabrook <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3462' width='330' height='300' border=0 style='border:none;'> on March 15, 2015, 10:16 pm, in reply to "Re: Leak off testing #"
Matt Seabrook

Got to agree with Jon. The Bosch training has been very useful so far and the VSD 15 has been a great insight to testing common rail issues. Mark is also a top bloke so even though it's 300 plus miles if you can't find a more local one course I would make the journey.

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