White puff of smoke at start only.. need your inputs !

[AVCUPRA290]

I'm sure that what you are finding, ie the HP fuel pressure rail staying at a very high pressure after warmed engine is OFF is not what is meant to happen, neither is the puff of smoke at warm engine start, but, I'd think that it would cost a lot of time and money to to sort this out, also most workshops would not consider this to be an issue that is worth investigating - ie they would not be able to guarantee to resolve it.

The indirect injectors should still be spraying atomised fuel in a predetermined pattern, so not just a valve that opens and lets "some fuel" through. I've owned indirect injection cars, typically cars with Bosch K Jetronic mechanical injection where the "injectors" were just spray heads that were forced open by high-ish pressure fuel being pushed down their supply pipes, even they could give this sort of problem, and with one car one injector did, Ford dealership didn't recognise it was being a problem, but after they had bodged up another issue, I ended up demanding that this "not correct" leaking of fuel into a single cylinder was not acceptable, so I bought a single new "injector" and solved that problem quickly - then went on to getting the originally faulty injector working, these K-Jetronic injectors were just spring loaded valves that were designed to vibrate while open and by doing that they should have always been able to "self centre" and so close and seal off fuel when the supply pipe pressure dropped - this one had ended up getting stuck/located so that it could not close properly. A friend that had a Ford Escort RS Turbo bought that injector from me and it seemed to help him solve a similar issue!

Edit:- I fully understand why you are digging deeply into this, but maybe try stepping back from it and enjoy your car - though easier said than done!

Hi mate,

First thanks to this forum (you guys) for pointing out the lead of a leaky injector.

I did dig a little deeper into this problem.

I first did every check I could was to re test my brand new OEM PCV, to make sure it wasn’t sucking oil (too high vacuum). Bought a vacuum gauge and found a 2.5-2.8 inHG vacuum at the oil dip stick which is what we are looking for (PCV regulation valve is designed to open/closed at -100mbars vs ambient pressure meaning the relative crankcase pressure you should have is 2.953 inHG so I’m right into it with a cheap gauge).
I did try to rev the car with my hand underneath aeration tube and when letting off the throttle the PCV does blows vapors within the inlet so correctly functioning.
=> PCV is juste fine (thank god that’s a pricey little piece of plastic)

As shown before the valve stem seals does not look « leaky » or dirty or baked from what I’ve seen from the manifold. And I have no oil consumption nor big smokes. So I think I can rule them out too, if this is the issue it is too minor for now (and I used 5w40 for my today service instead of 0w30 so might reduce it even more).

i introduced my issue to the mechanic who performed the service on my car and he did mentioned the indirect injectors. on the last pictures Ive shown you the liquid inside the cylinder was looking like dirty petrol more than oil so I also thought about petrol coming from the manifold (this dirty) + the pictures showing black liquid deposit shown previously happened with the tank full of injector cleaners + few Seat dealers mentioned the leaky injectors as a known issue.
I did find those indirect injectors at a fair price so took 4 of them.
I bought 4 new spark plugs too.
And the oil is new.

I will keep you updated on the results on this (there is still a chance the smoke is not coming from these injectors - might be the direct ones - or might be coming from elsewhere and be indeed oil) but I’ve looked everything I could and in the end for now it is not that big of an issue !

thanks again