Renault 1.9 dCi: Starting Problems Below -2°C

Hello,

(hopefully I've chosen the right subcategory)

Vehicle data:

Renault Laguna 2.
Year of manufacture: 2002, Phase 1.
1.9 dci / 107 hp
Engine: F9Q-754
No VTG loader.
Not CAN-diagnosable.

Since this winter, my DCI has been having trouble starting when the temperature drops below freezing. Specifically, if it sits outside overnight in sub-zero temperatures, it starts very poorly in the morning. It's as if not enough fuel is getting to it. However, once the engine *does* start, it runs very smoothly. If I turn it off about 15 seconds later and don't restart it until the evening, it starts without any problems.
Very rarely, I notice that the idle speed briefly drops about 100-200 rpm below normal when the engine is warm. (However, this improved after I performed a diesel system cleaning using a specific cleaner!)

I have already checked the diesel filter and the high-pressure system for visible leaks. Unfortunately, there are no error codes stored in the diagnostic memory either.

At the same time, I visited a workshop and asked for advice there. They suggested that it's possible the injector seats in the cylinder head could have been washed out. But can that happen within a year? I bought the car with a worn timing belt. (All pistons were intact, and only 2 valves were damaged --> but all were replaced). What I want to say is, the injectors had already been removed once, and after the repair, the car started perfectly fine. (The cylinder head was professionally overhauled --> it wasn't a cheap job). The repair itself took place 2 years ago.

I can create logs, but unfortunately not with VCDS, but with the Renault CanClip instead.

I hope someone here knows something about a DCI... but I would appreciate any answers you might have!

Sure, no problem! Here's the translation:

"Thank you in advance!"

Hey, nice list! Does it include the heating system?
Is the fuel system leak-proof?

Oh yes, I forgot to mention!

I have checked the heating system and also replaced the glow plugs.

Well, I've already tried checking for any leaks in the high-pressure system, but only visually.

Could a leak from the diesel filter to the high-pressure pump also be the cause? At least, you can't see any visible leaks when the pre-pump pumps fuel into the diesel filter. However, the filter is already slightly oily. Could that be a reason for concern?

Shortly after installing the cylinder head, I cranked the engine for a total of 1 minute without connecting the fuel rail connector in order to get oil into the turbocharger. However, doesn't this actually prevent proper venting of the high-pressure line because the injectors don't open? Or am I mistaken? In any case, the engine started immediately afterward. This was in January 2011.
THAT'S WHY I think a small leak in the line before the high-pressure pump shouldn't be a problem.
I hope I'm wrong.

EDIT But you also gave me the idea to do the same process as shortly after the cylinder head assembly...

Why wasn't the coolant temperature sensor checked?

Investing in repair manuals and "do-it-yourself" books for the vehicle would be more than worthwhile. Of course, one should read them before starting to tinker around aimlessly.

It's quite foolish to replace the glow plugs based on suspicion alone. There is always a certain risk that one or more glow plugs will break off if you try to force them out.
If the glow plug is not properly tightened, taking into account the correct torque, closing the ring gap at the back of the glow plug will result in too low temperatures at that (measurement/control) point, and consequently, overheating of the heating element. The new glow plug, incorrectly installed, will fail very quickly.

Overall, I strongly advise acquiring at least a basic understanding before resorting to hasty and reactive actions.

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