Help diagnosing fault

[RS4_Ollie]

Hi could anyone help with a bit of diagnostic with my car.

I have been having a knocking noise at random intervals from start up for the last week, some time lasting a minute or two sometime lasting 30 seconds. It has happened about 6-8 times out of about 25-30 starts all at random time ie not when oil is cold or hot or been sat for a while or not etc...

The noise is coming from the rear intake side of bank 2. I thought it could be the HPFP so i changed them over side to side including followers but the noise remained on bank 2.

I think I have narrowed it down to the intake cam adjuster.

I managed to get some logging done when the noise has been happening.

I logged intake cam adjuster duty cycle, requested and actual adjustment.

Graph when knocking noise is happening Red: duty cycle, Green : Req, Yellow : Act



This is when the car is running OK



I'm pretty sure this means the intake adjuster is fooked but Id like to just confirm it first as its a £460 part.

Id be glad of any constructive info?

Oh and it has no DTCs at all to do with this issue

[audi_do_dat_den]

How long between stopping the engine and restarting is it when you get the rattle?
Does it rattle for less time with a hot engine or is it totally sporadic?
Also, is it a slow tapping sound or a fast and harsh grating noise? Does it sound like harsh buzz, a bit like when you clipped a playing card against your bike wheel as a kid to make an engine sound... (am i showing my age here... )
The reason i ask this is because the camshafts have a hydraulic tensioner for the chains.
If the tensioner loses its oil while the engine is off, you will hear a brief clatter until the tensioner is re-pressurised.
I would be more inclined to think that the tensioner is the culprit rather than the cam adjuster.
The rotary cam adjusters only add or decrease a few degrees of advance/<beep>, therefore even if at their default failsafe position, you wouldnt get any sound from them.... maybe a CEL but they are still whirling round.
If the tensioner piston is relaxing, then that could be a poor seal in the tensioner itself, or the main oil check valve in the filter body or in the pressure discharge side of the oil pump.
The oil filter is up high on the top of the engine and if its draining down while the engines off, then obviously there will be a few moments until the oil reaches the filter apon start-up.....

[audi_do_dat_den]

....some time lasting a minute or two sometime lasting 30 seconds. It has happened about 6-8 times out of about 25-30 starts all at random time ie not when oil is cold or hot or been sat for a while or not etc...

Oops.... thats answered that question..... should have read the post a bit slower

As the noise youre getting is coming from the rear end of the engine, it figures that its a chain tensioner related issue.... thats the chain drive end anyway.

[RS4_Ollie]

There doesn't seem to be any regularity to it. It has happened first start of the day and it has also not happened all day then happens after being off for 30 seconds.

The sound is like a tap tap tap tap not like a chain noise, i thought it could be a sticky lifter at first.

I happens for anywhere between 30 secs and 2 minutes roughly when it has happened.

The check valve in the filter housing would be a good shout as it happened the day after an oil change so that's something to check I guess.

[audi_do_dat_den]

Definitely worth checking that out, although im not sure if its actually in the filter housing base or in the pressure chamber line after the filter.

As its a slow, sort of half engine speed, tapping sound, you could well have a weak cam follower on one valve.
I have a feeling you mentioned in a previous post about the oil viscosity grade spec being changed at a recent oil change.... a change of grade or even a change of brand can often cause a few new noises to appear.
Years ago, i had a 1.8 225 TT that was fine until i changed the oil from Audi longlife to Mobil one... and then onwards it always rattled for a couple of seconds from the cam chain tensioner on start-up.

[RS4_Ollie]

Yeah, I changed to regular service oil 5w40, 505 as it is said to combat oil consumption. The next day after i had used it a few time i got in after work and tap tap tap tap. I shat myself and immediately doubted the oil and drained it and went back to the longlife 5w30 507. The noise stopped and I hoped it had cured it.... now this ^^^. I cant help but think it must be to do with the oil but at the same time it 'could' be coincidence.

[RS4_Ollie]

The reason I don't think its chain tensioners, apart from the noise is that they (correct me if im wrong) are on the slack side of the arrangements so they wont affect the timing just be noisy.

I cant see how if it was chain tensioners the cam requested vs Actual would be like above?

[audi_do_dat_den]

I see what youre saying.... but the adjusters wouldnt allow the valves to touch pistons even if fully retarded or advanced.
If the adjuster was shagged completely and collapsed, then you would get a permanent noise and from all four cylinders on that bank.... also, if the adjuster was bad, you would likely have a missfire and then a CEL.
Yes the tensioners are on the slack side of the chain, but from what youve described, the noise is a cam follower related issue....

[RS4_Ollie]

I thought the same and thought it had to be a sticky lifter/follower until i saw the data above.

[audi_do_dat_den]

Need a VCDS guru to help here, to confirm or explain the data youve got vs what is actually acceptable.

Somewhere in the live logging ability, theres a measuring block to read the knock sensor/missfire counts.... im not sure which one it is, but i know you can read it live.

Say for instance, you have a lazy follower thats losing pressure when static, then it might be possible that the ECU is reading a missfire on that cylinder and briefly panicking to resolve it, hence a sudden shift on the cam timing..... might be speaking out of my arse, but the graph you are seeing is possibly the result of the ECU trying to balance things up... and throwing a red herring in there....
If anything was consistently giving errors, then the ECU would log it after a set number of events and then illuminate the CEL.

Have a look at this PDF for the self study guide, go to page 18, it shows the oil check valve setup in the oil circuit.
http://www.vaglinks.com/vaglinks_com/do ... Engine.pdf

Im just popping my asbestos overcoat on, just in case i get an imminent proper flaming from a resident VCDS/ECU wizard...

[RS4_Ollie]

I thought as the are no misfire codes that there wouldn't be anything in those block. Does there have to be a certain number of misfires before it logs a code?

[audi_do_dat_den]

I think so.
Im not sure of the number but i think theres a sort of buffer zone before it decides that theres too many to ignore.

[RS4_Ollie]

Can anyone comment / help on the camshaft adjuster logs?

[RS4_Ollie]

Thought Id just update this in case it helps anyone that reads this thread.

The noise turned out to be the left side cam chin tensioner not keeping tension letting the chain run loose(er).

I beleive the chain was trying to jump the sprocket on the inlet cam but the chain was obviously not quite slack enough to jump, this is why (I think) I was getting the angle deviation from spec. to actual on the inlet cam. I cant see any other reason for it as the inlet adjuster was in perfect working order.

I could also see from the wear on the end of the tensioner pistons that the chain has been loose.

Anyway on closer inspection after removing the cam chain tensioner I found that the strainer had a section missing.



Missing section of strainer


I found the missing piece inside the exhaust cam adjuster