Extreme camshaft deviation

I've been researching a strange noise coming from the rear of the car as I engage the clutch from standstill/at low speeds, a bit like "faff faff faff". It only happens when the engine warms up. I've had the gearbox out at a specialist, the clutch is healthy, brand new flywheel, greased appropriate parts, yet the sound persist :? My next guess was the chains, but I don't have the common rattle at startup nor have I seen any plastic bits in the oil. Replaced the IMS tensioner without any change. I then went to measure the camshaft deviation: Actual position is less than 1 degree on both banks at warm idle, but jumps up to >20 when I rev the engine (normal?). More worrying are the extreme values of 1020 and 380 degree deviations – Any guess to what that means? The engine is otherwise healthy and has good power.

Hi I'm sure someone more knowledgeable than I will be along soon, but camshaft deviations can sometimes be a symptom of a worn IMS bearing, or Variocam solenoid issues. Hope its nothing serious! Berni

Hi, thanks for replying! The IMS bearing has recently been replaced, so probably not, but I did consider that it could be Variocam related. Just don't understand how that would create such a strange value, or if it's even related to my mystery rattle. Trying the forums for ideas before paying any more to my already well paid mechanic :lol:

When you rev your engine the cams are advanced - that's the whole point of variocam. Doubt your noise is anything related to your cams......or IMS. Might help if you record the noise and post the clip on here.

Appreciate hearing from you Alex. My initial thought was that it must be clutch-related as the noise only appears when releasing the clutch, but all moving parts expect the transmission itself or the slave cylinder (?) should now be eliminated... Thus looking into chains and cams. Not that I know much about those. I will make a video as soon as possible.

From how you've described it, I'd say its more exhaust note changing from when the engines runnig rich (when cold) to when its warm. Need to hear it.

Does it happen whether the car is stationary or moving? Does it vary with engine speed?

The sound seem to correspond to rpm and only occurs when engaging or releasing the clutch (however not when cold). I guess the sound is always there when changing gears, but is only audible at low speeds when starting or coming to a stop. Which is why I was certain that it must be the clutch or flywheel :frustrated:

Hmm. If the only symptom is the noise, ie no judder or hesitation, I'd live with it and see if it change as things bed in. I appreciate that's perhaps not your preference though!

Your cam deviations make no sense to me i'm afraid .. you cant have more than 360 degrees ? I had a deviation of 21 degrees last week which was the variocam unit .. early car so not variocam plus . That didn't make any noise .. depressing the clutch and the noise will be related to that .. the deviation .. that's not a plausible signal from what i can see considering the actual adjustment would be in the ballpark . I'm assuming that's a cold engine as the injection duration is pretty high .

Here is a video of a gentle start . With more revs the noise is either drowned out or disappears, unsure which. It's annoying and quite embarrassing when parking. My current best guess is a rattling chain, which is also why I started looking to the cams (although they are unlikely the cause.) I just don't understand why operating the clutch at low rpms with a warm engine would cause it to rattle, otherwise remain silent, and no other obvious symptoms of a loose chain...? I do have Designtek engine mounts but can't remember if it started after installing them, they're not particularly harsh. As a possible solution I am considering using a thicker oil than my current 5W40 (only drive in summer) and replacing the remaining two tensioners.

Yeah sorry maybe I'm mixing the issues. I don't think the cams are making the noise, but I do believe it's related to some chain, having excluded the clutch and flywheel as a source. Other suggestions are welcome! The engine is running at warm idle. Here is the video . I thought the nonsense deviations were the only problem in the readout and fishing for some ideas for may cause them, but what does a high injection time indicate?

First off .. check for an exhaust blow .. yeah i know it's unlikely but that noise does sound to me like an exhaust blow and possibly around a lambda sensor .. that if it is that would explain the high injector duration . Ok so injector duration .. this is the amount of time the injectors are open for in milliseconds .. the higher the figure and the more fuel is being injected .. Injectors are open for longer ! Flat out and about 11 m/s from memory .. A hot engine on idle stationary and i would expect about 1.5 m/s give or take a little . 3.5 cold , idle and that's about right . This is all down to adaptations though .. a slight air leak and the duration will alter to compensate .. as such it's fine as the car is basically adjusting to a small issue ... this may or may not be an issue as if its adaptations then its not . Your noise though .. very unusual .. stationary its fine but on take off it does this .. so i'm thinking what would alter .. engine load and clutch operation is all i can think of .. Clutch .. well not a noise i've heard from a clutch before .. i could at a push say release bearing is faulty .. but that's a bit of a long shot .. the noise sounds like something is flapping around .. something metallic .. Sports exhaust fitted ? the valves do make noises when loose . Tensioners .. well .. again not a noise i've heard .. its possible .. i guess .. replacement is the only way to prove though .. i kinda doubt this being the issue but these days after so many weird faults i can never rule anything out . They tend to rattle on startup until filled with oil for about 3 seconds and are quiet after that .. so it doesn't really fit your issue . I don't tend to trust testers that are non Porsche .. the deviation you have listed .. that's not right .. the injector duration again might not be .. I know full well some of the data i see on Porsche testers is incorrect .. hence im always dubious of what any tester tells me . For me .. i would have the car on a ramp and run it to try and locate the noise .. if under a load only then it would be difficult .. we can put it under a load like this but only for short periods by using the handbrake . Noise sounds like an exhaust leak so i would certainly rule that out first . A difficult one i'm afraid .. it doesn't ring any bells with me so i can only go with what i feel .

I appreciate your detailed response, deMort, and apologise for the late reply. I realise it's not easy to diagnose like this and the microphone also isn't helping. I do have a Dansk sports silencer (no valve), but I'm pretty confident it's coming from somewhere in the engine or drivetrain – as the noise follows rpm and only appears after warmup, and only with the clutch pedal partially depressed. Release bearing is a possibility but I had assumed my mechanic would've noticed when recently replacing the flywheel (?) On your suggestion I will carefully get it up on my Quickjack with the engine running and try to isolate where the noise is coming from. I will also come back later with a video from the driver's seat, perhaps that's easier to hear. I guess the crazy cam deviation (and other...) readings will be for another chapter. At least the engine seems to be running smooth for now, despite everything I've mentioned!

(double post)