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Old 9th April 2022, 19:45   #21
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Thanks for those suggestions .... now the T4 check has eliminated a set of possibilities I'll be running through some different checks ... Although I checked for obvious leaks 'upstream' of the engine I haven't looked further as my previous experiences with leaky intercooler/feed pipes was that it gave plenty of smoke but it was sooty and black (my smoke is blue and light coloured) .... if intake leaks can cause blue smoke I'll certainly recheck all of that more thoroughly. .... I certainly don't claim in depth knowledge of modern diesels

Cheers

K

K
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Old 9th April 2022, 20:45   #22
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Thanks for those suggestions .... now the T4 check has eliminated a set of possibilities I'll be running through some different checks ... Although I checked for obvious leaks 'upstream' of the engine I haven't looked further as my previous experiences with leaky intercooler/feed pipes was that it gave plenty of smoke but it was sooty and black (my smoke is blue and light coloured) .... if intake leaks can cause blue smoke I'll certainly recheck all of that more thoroughly. .... I certainly don't claim in depth knowledge of modern diesels

Cheers

K

K
How about 'Downstream' of the engine. A worn turbo with leaky seals ??

Engine oil into the exhaust giving blue smoke.---
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Old 9th April 2022, 21:17   #23
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Indeed .... that's one scenario I'm prefering not to think about

Gradually working through the possibles with the cheap and accessible ones first ... but eventually I'll have to bite the bullet, remove a load of plastic and delve down the back of the engine .... what is strange is that it smokes when cold and once warm neither hard acceleration nor hard engine braking effects the smoke .... wouldn't those more expert than me expect the manifold vacuum to draw more oil past the seals into the intake side on over-run and hence give more smoke if the seals were gone??

K
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Old 9th April 2022, 22:49   #24
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Indeed .... that's one scenario I'm prefering not to think about

Gradually working through the possibles with the cheap and accessible ones first ... but eventually I'll have to bite the bullet, remove a load of plastic and delve down the back of the engine .... what is strange is that it smokes when cold and once warm neither hard acceleration nor hard engine braking effects the smoke .... wouldn't those more expert than me expect the manifold vacuum to draw more oil past the seals into the intake side on over-run and hence give more smoke if the seals were gone??

K

I think you are thinking of the phenomena of worn valve guide seals where an engine would smoke a lot after being stood a while and started, due to the oil seeping down the stems, finding it's way into the combustion chamber and the back of the exhaust valves where it got burnt and cleared after a short while, with very little smoke thereafter even under hard acceleration.


However, with foot off the pedal and say cruising down hill on overrun a brief puff of blue smoke was seen as the accelerator was depressed this confirmed in most cases worn guides.


This is due to an engine which incorporates a throttle valve/plate in the inlet system, (not to be confused with a throttle body) which when closed on overrun it creates a high vacuum, (not the correct term but one every one understands ) in the inlet tract drawing oil down past the stem seals.


However, throttle plates are mainly on petrol engines, with very few being used on diesel engines, the 75 engine doesn't have one and other than excess engine crank case blow by, inefficient PCV or oil mist from the turbo, there are no other places that oil can be introduced into the inlet tract.


There is also one fault that can give the same problem of smoke at all times which is worn piston rings and bores especially oil control rings which can sometimes suffering from varnishing and gumming preventing efficient bore wiping.


The first thing you need to do is identify if the smoke is from oil or derv sometimes your nose is the best test.


Smoke from derv can be blackish or white, black resulting from insufficient air or excess fuel for various reasons, white being unburnt fuel again due to various reasons.


Blue is oil.


Occasionally due to oil dilution by derv which ' thins' out the oil, this ' thinner oil ' can pass the rings.



Has the problem been building up or has it suddenly happened ?


Is there copious oil in the intercooler pipe work, there is always a bit.



Non of the above points to the actual problem or cure but may help you to look at different areas.
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Old 10th April 2022, 15:57   #25
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Thanks for that .... my expertise is more towards old carb engines rather than modern diesels ��

The problem started with fitting brand new injectors .... it didn't smoke before but did after (changed as excessive leakback caused starting issues .....using genuine new Bosch injectors from a reputable diesel specialist)

As the car was parked up for just a few days while I sourced the injectors I can't see valve seals, rings or turbo seals spontaneously failing while it was parked less than a week.

I think it's more likely something I've done (or not done) during the job (or an injector that's faulty from the factory) .... maybe I pinched/disturbed something while removing/replacing the manifold? (slightly annoying design that you have to strip so much to change injectors).

Of course, all the above could be wrong �� ... just my assumptions.

Nothing showed up on the T4 check so I'll keep worrying at it using first-principles until I get to the bottom of it.

Cheers

K
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Old 10th April 2022, 19:30   #26
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...something I've done (or not done) during the job (or an injector that's faulty from the factory) .... maybe I pinched/disturbed something while removing/replacing the manifold? (slightly annoying design that you have to strip so much to change injectors).

K

Did you use new sealing washers for the injectors and clean the holes out before fitting the new ones?



Maybe a slight compression leak that seals once the engine has warmed up is causing the smoke and miss fire?
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Old 10th April 2022, 22:20   #27
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Have you thought of polluted diesel from a petrol retailer?
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