FSI Diesel start up x oil viscosity

Hello,
I've spent an hour or so reading the following document.

Self-Study Programme 253
Direct Petrol Injection System with Bosch
Motronic MED 7
Design and Function

Engine Management FSI ONE.JPG

These sensors report DATA to the ECU


FSI Engine Management two.JPG

These items are controlled by the ECU

Inake system FSI.JPG

This is the air intake system and the vacuum-controlled items

FSI_INTAKE_NON_RETURN_VALVE.JPG

The one-way valve maintains the vacuum in the vacuum box when the engine shuts off. Could this cause the start-up rattle?


The FSI is all about the air, with its three modes of combustion depending on the torque demand.

The self-study programme that this lot came from is easy to follow and from page 16, it starts to get interesting.
Especially the information provided about each component when there is a signal failure and the strategies it employs.

G294 brake servo pressure sensor
If the signal from the pressure sensor fails, the
engine will only be allowed to operate in
homogeneous charge mode.

Its full of nuggets like the one above.

My concern about this engine would be the availability of new and used parts.
 
As advised by others, the start up "clatter" is purely down to the hydraulic lifters. The lifters are like hydraulic rams, expanded by engine oil pressure, to maintain contact between the Camshaft Lobes and Valve Stems. The oil pressure maintains the necessary pressure to overcome Valve Spring tension.
When the engine stops, oil pressure decays, and Valve Spring tension on any open valves becomes the dominant force. Thus the Lifters are compressed, until the Valves fully close. The degree of compression will vary, depending on which Valves were fully or partially opened when the engine stopped. These positions will most likely be different at each stop.
When the engine is started, oil pressure build up is not instantaneous, so the shortened Lifters clatter between Cam Lobes and Valve Stem, until fully opened. Thus a warm/hot engine will clatter for a shorter period than a cold engine.
The important thing is to maintain the oil cleanliness, and the specified viscosity. Lighter oil will cause the Lifters to relax more quickly, but not necessarily allow quicker expansion on re-start.
Heavy, worn out, dirty oil is the enemy of hydraulic lifters!

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Jellybean said:
As advised by others, the start up "clatter" is purely down to the hydraulic lifters. The lifters are like hydraulic rams, expanded by engine oil pressure, to maintain contact between the Camshaft Lobes and Valve Stems. The oil pressure maintains the necessary pressure to overcome Valve Spring tension.
When the engine stops, oil pressure decays, and Valve Spring tension on any open valves becomes the dominant force. Thus the Lifters are compressed, until the Valves fully close. The degree of compression will vary, depending on which Valves were fully or partially opened when the engine stopped. These positions will most likely be different at each stop.
When the engine is started, oil pressure build up is not instantaneous, so the shortened Lifters clatter between Cam Lobes and Valve Stem, until fully opened. Thus a warm/hot engine will clatter for a shorter period than a cold engine.
The important thing is to maintain the oil cleanliness, and the specified viscosity. Lighter oil will cause the Lifters to relax more quickly, but not necessarily allow quicker expansion on re-start.
Heavy, worn out, dirty oil is the enemy of hydraulic lifters!

Sent from my SM-N960F using Tapatalk
Click to expand...
While this explanation makes sense and I agree is probably the cause of the noise, it does strike me as a bit odd that there are no mentions of the noise before about 2010, or none that I could find over the course of a few google searches anyway…
 
N
Indi said:
While this explanation makes sense and I agree is probably the cause of the noise, it does strike me as a bit odd that there are no mentions of the noise before about 2010, or none that I could find over the course of a few google searches anyway…
Click to expand...
I understand your logic, but when I got my 2004 FSI, in 2019, it had just over 40,000 miles on it, equivalent to maybe five or six years of average use, full Audi service history, and only two previous owners, the first from new, for thirteen years. Nearly six years and getting on for 20,000 miles later, it's still the same, so I don't think it's age related. It's a cliche, but in this case,probably true, "they all do that Sir"
More a dull tap, rather than a harsh metal on metal rattle. I'd miss it if it wasn't there.
Mac.
 
Anyone reading this thread, who hasn't heard "it" first hand, would be very wary of an FSI, and would be seriously mislead as a result.
If you haven't heard "it" first hand, let me assure you it is not like a diesel on start up.
Not even like a diesel when warmed up, (apologies to the TDi afficanados).
It lasts a couple seconds, literally, then it's gone, completely.
If you're really interested, make an effort to hear "it" first hand. Then make your own mind up.
Mac.
 
Guys, don't mean to hijack this thread, but could one of you help...

Today I came to finish off renewing the Fuel Hoses on my FSI. However, despite taking loads of images when dismantling, I have found there's no substitute for old tech... a pencil n paper sketch! Lesson learned.
Could FSI owners please verify that the connections shown on the attached diagram are correct?
For anyone carrying out this job, the connection under the Inlet Manifold is an utter swine to access!
87017d929176beaf7b5c46e9314ad674.jpg


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