FSI erratic/uneven running

OK, that sounds sensible. :)

I had a brief call with the diagnostics shop guy again. He was repeating that they think the problem was in the intake cam timing adjustment system. He was also suggesting that the typical BAD starting sound ("something being filled with oil", the one we all know..? At least I thought so!) was actually coming from exactly that timing unit. He stated they think it really should not do that. Of course they have no previous BAD experience. And anyway, still no explanation why fault codes for the cam timing were missing if it really was broken.

This was interesting anyway, as I have never read anybody stating noise would come here, but from the high pressure fuel pump or valve lifters (?)

Edit/disclaimer: I have only once driven one other A2 1.6. I do not remember at all how its engine sounded during startup. Mine has made the sound since I bought it (4 years ago or so). It lasts only a second or so, and based on what I read I thought it is a "feature" and wasn't worried at all.

Edit 2: A friend mentioned about Maserati cam variator issues. My A2 "start noise" tone is lower frequency, but I'd say basically it is not horribly different from this: https://www.youtube.com/watch?v=37Y2xRXtjs8
 
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Mine makes the same awful noise on startup, it's just the oil getting to the top end, I've noticed mine does it less with fresh oil but it's never bothered me.

The part I cleaned was behind the black plastic case on the throttle body, I removed the clips and gently removed the case, inside is the motor and an arrangement of brushes and tracks that give position indication/feedback and a set of gears and a belt between the motor and the throttle butterfly. The whole lot gets caked in carbon dust from the motor. Mine was jumping all over the place and the action wasn't very good at all, contact cleaner sorted it out.

The brushes are fragile so be careful but other than that is quite straight forward.
 
My perfectly running one makes the fart noise on startup every time. I'm guessing this is normal behaviour.
 
My perfectly running FSI strongly sounds like a Diesel engine for a couple of seconds on startup. To the extent at least two passengers have asked me if its diesel.

Andy
 
Thanks for confirmation! This is what I had read before, and did not worry about the sound for years. :)

As a side note, that Maserati cam variator video made me think could the startup sound in BAD really originate from that device (even from a healthy one)? :rolleyes: I understood that even in those engines variator actually works ... as long as that noise eventually stop and does not continue all time. :D I do not remember ever seeing a thorough explanation what exactly causes this sound in BAD. (Another question is, does there exist BAD examples without it?)
 
I think it's oil getting to the top end, specifically to supply oil to the rollers on the rockers, when new the tolerances were probably perfect but with age there is probably a bit of wear so on initial startup the cams contact the followers until the oil layer is formed.

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A quick update. I got my car back from the diagnostics shop and did some logging yesterday. Seems like they were right at least partially with the VVT. After the engine was properly heated up and restarted, cam timing really did stop following the set value! It got stuck several times (bad power loss, significant misfire). However, when letting engine idle the timing seemed to follow setting. It also started without any issues, like always. Perhaps lower oil pressure allowed the cam variator or its control solenoid (N205) do its work properly?

I didn't notice anything obviously weird with high-pressure fuel readings.

There was still slight misfire noticeable even when cam timing was seemingly working. I hope this was related to timing issue too (just acting too slow, or something), but we'll see.

My current idea is to remove & try cleaning the N205 solenoid. I read from several sources about heat-dependent issues with those solenoids. The camshaft adjustment unit costs 600-800€ and requires quite a lot work to replace, so probably I'll even replace the solenoid before the unit itself.
 
Interesting... There is a small filter that sits between the rocker cover and cylinder head specifically for the N205 and Cam variator, I was supposed to replace mine but completely forgot (I realised just as I finished bolting the rocker cover down). I summarised that with age, the filter seal (essentially an O-Ring with a gauze in the centre) had become brittle and was allowing oil to pass between the seal and back into the top of cylinder head and not supplying sufficient pressure to the variator. Given that I still get occasional error codes for intake cam position being excessively advanced, I wonder if this is still ringing true.

Certainly cheaper than a new variator, a little tricky but not difficult. (Involves removing both cambelts). For me, the code is so intermediate that I'm not overly fussed.

I wonder if anyone has ever taken the variator apart?

Nick
 
Thanks for information again, Topsie!

I guess the mentioned filter is the "oil strainer" (now obsolete 036 115 175 B)? I hope mine is OK, since top of the engine was rebuilt just in January. But who knows

I've not found any traces about anyone opening or trying to fix these variators. I've been told those just wear out mechanically, so cleaning or oil wash would not help. Only repair kits I've found are for some Audi V8 engines (to replace worn parts). The only temporary "repair" is supposedly using thicker oil. But there are still things I'm not fully understanding. Obviously engine oil (and variator itself) get hot when standing, causing oil density drop quite a lot. Viscosity changes too. Does the variator then start leaking too much, does the solenoid get stuck, does general oil pressure drop too much, ...?

Perhaps I should make a new thread about this cam timing adjustment issue. It seems like not much has been written about it.
 
I've fancied the idea of stripping one down however you do need to be able to time it properly on assembly. I would purchase one to play with however they are both rare and expensive, even 2nd hand...

Looking at the SSP252 the most likely candidate for failure is the 'sealing ring' between the piston and the cylinder, however without taking the Camshaft Adjustment Unit (CAU) apart, I've no way of knowing if this sealing ring is metallic or non-metallic. In a perfect world it would be an O-Seal (kind of like the BMW VANOS), which could be easily replaced.

Interestingly, noise on start-up is eliminated by the internal spring pushing the CAU to the retard stop position, which is why I don't believe the CAU is the primary cause of noise on start-up, the spring isn't under extreme temperature or stress so relaxation or creep is minimal.

Anybody got a spare CAU hanging about in the garage? :cool:
 
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Im confused as I'm pretty certain the 1.6 Fsi BAD engine is not vvt. The cam chain versions are. But not the versions in A2's unless I have been wrong for many years owning my FSI. cheers Mike
 
They certainly are, the Camshaft Adjustment Unit is on the end of the inlet camshaft - on the 1.4 engine the cam pulley is a bit like a hallow drum however on the FSI this contains the CAU. The other giveaway is the N205 solenoid valve on top of the free-end of the rocker cover. The 1.6 FSI is essentially the same as the 1.4 FSI "ARR" engine used in the VW Lupo. SSP-252 is a good read.
 
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I thought that was the cam position sensor - the unit ant the end of the cam shaft is the high pressure fuel pump ? Off now to look at pics of the engine cheers
 
That's the Drive-End, I wish the BAD wasn't VVT as it just makes everything that little more complicated!
 
Hello, salutations from Spain.

At the end has solved the initial problem of the post?

I think I have a similar problem in my a2 1.6 FSI. My car has no strength until 2600 RPM, pulls a little, consumes a lot (10 liters) and is very retained.

You have changed the spark plugs, coils, coolant temperature sensor, fuel filter and air filter.
Also the MAF sensor was changed and the car remains the same. The only thing I noticed is that when I turn off the MAF sensor the car goes better.
The vagcom does not give errors of any kind, only sometimes had some spark failure in some cylinder.

Any idea where to go? Injectors? High pressure or low gas pressure? Empty tubes?

Thanks in advance, greetings to everyone

P.D:I can not see in the vagcom the values of the injectors, nor the consumption. I think I'm missing a more up-to-date label. Any ideas on this?
 
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