Random cranking issue, M57 diesel 2003

[andrewwynn]

You didn't notice the slower start because it takes years to get slower so it's normal. How people usually notice is when they meet up with somebody with the same model but newer car (or newer starter). Sadly more often than not they've already replaced the battery thinking the slower cranking is from weak battery. Hope your problem is fully resolved. That's a great engine you should have at least a few more years in that car.

[Clavurion]

Originally Posted by andrewwynn

You didn't notice the slower start because it takes years to get slower so it's normal. How people usually notice is when they meet up with somebody with the same model but newer car (or newer starter). Sadly more often than not they've already replaced the battery thinking the slower cranking is from weak battery. Hope your problem is fully resolved. That's a great engine you should have at least a few more years in that car.

Same thing as with leaky injector which makes the start gradually slower (rail pressure build up is slower). When somebody comes to diagnostics I can say from the first start if there is a worn injector and start takes more cranks than it should.

[wpoll]

Originally Posted by Clavurion

Same thing as with leaky injector which makes the start gradually slower (rail pressure build up is slower). When somebody comes to diagnostics I can say from the first start if there is a worn injector and start takes more cranks than it should.

Interesting... Would there be other indications of a worn injector?

Things like checking the selective mass adjust values in INPA and/or the smooth idle tests etc?

[Clavurion]

Originally Posted by wpoll

Interesting... Would there be other indications of a worn injector?

Things like checking the selective mass adjust values in INPA and/or the smooth idle tests etc?

This mentioned leak off problem indicates worn internal sealing. You can measure leak off with measuring hoses and cups (I've used 20 ml syringes). Usually good injectors are below 20 ml leak off @ 2 min idle.

Correctional values (smooth running control) tells more about the condition of injector nozzle (fuel atomisation properties).

[wpoll]

Originally Posted by Clavurion

... Correctional values (smooth running control) tells more about the condition of injector nozzle (fuel atomisation properties).

So an injector could be leaky but the Selective Mass Adjustment values would not show that. Good to know.

[Clavurion]

Originally Posted by wpoll

So an injector could be leaky but the Selective Mass Adjustment values would not show that. Good to know.

Yes. They don't have direct correlation. The leak in this case is to leak off line, not in cylinder. There is some leak off due to working principle of common rail diesel injector. If the internal teflon seal between injector body and needle fails some of the high pressure fuel leaks to leak off side. First this will show as a slower start and eventually it can prevent engine start because required fuel pressure is not met. In some rare cases this can also stall engine on high load because of too high discrepancy between rail pressure demand and true value.

Poor correctional value will show as uneven running characteristics on idle and low RPM.





On attached picture quite typical failed teflon seal.