Resonant engine rattle on the over run

[mascanes]

Oh great technical people of this forum, I have a question for you all "¦"¦"¦..[8D]

Some time ago I mentioned on the forum while answering another post that I get a very interesting type of engine type resonant rattle on the over run. It kicks in almost exactly at 2900rpm until 3200rpm, but only on the overrun. It never happens when powering up through rev range, or coming back down through it. Well the great guys at Hatfield had it in for all of last week and decided after much checking that it was exhaust related. So now I have two brand new exhaust boxes courtesy of Porsche warranty. Guess what? the noise is still there[]

The problem is that it's right around the cruising speed. So say on a flat road for example in the cruise you can hear it quite a lot. According to Hatfield when they contacted the Porsche gods after the noise didn't go away, I assume at Reading, they were informed that it is a phenomenon in some engines and not to spend any further warranty time investigating it. Other than that the engine is as sweet as nut. It actual spoils some of the driving pleasure when it kicks in.[]

Many many years ago I had a company Mondeo and it was common for the "cats" to break-up and start rattling. Anyone heard of this happening to Porsche engines?

Any thoughts on this from anyone would be really appreciated"¦"¦"¦"¦"¦[8|]

 

[tscaptain]

I have a question for you first Mike! You say in comes in from 2900 to 3200 but on the over run? If the engine is on the "over run" then you are off the gas and the revs decreasing not increasing - or just feathering the throttle to maintain a constant speed?? Or does it rattle going up and coming down? Presumably they checked for loose heats shields and stuff?
I'm certainly no expert in this area (or any other for that matter!) but I would have thought that cats breaking up would rattle most of the time. That rev range (around 3200 from memory) is, of course, when the changeover happens inside the engine with the valves/camshafts (variocam) etc.

Do you have PSE? If so is it different with it on or off? Does it rattle at those revs when stationary?

Sounds like another trip back to the dealer.........[]

 

[mascanes]

ORIGINAL: tscaptain

I have a question for you first Mike! You say in comes in from 2900 to 3200 but on the over run? If the engine is on the "over run" then you are off the gas and the revs decreasing not increasing - or just feathering the throttle to maintain a constant speed?? Or does it rattle going up and coming down? Presumably they checked for loose heats shields and stuff?
I'm certainly no expert in this area (or any other for that matter!) but I would have thought that cats breaking up would rattle most of the time. That rev range (around 3200 from memory) is, of course, when the changeover happens inside the engine with the valves/camshafts (variocam) etc.

Do you have PSE? If so is it different with it on or off? Does it rattle at those revs when stationary?

Sounds like another trip back to the dealer.........[]

Hi "¦"¦.. Yes that's probably a better description, more just feathering the throttle I suppose ......just off the gas. No It doesn't rattle going up and down. Yep, they've gone through the heat shield checks as well. Interesting that when I looked underneath this afternoon I noticed they have left the manifold to silencer pipes unchanged though, I suppose there just pipes with nothing in them

I had to go on trip this past week so they had it for the week so were not rushed, I feel they've been fairly thorough.

Good point about the cats, yes they would rattle all the time. Interesting what you say about the variocam operation though. I'm definitely taking it back, when I do I will mention this to them "¦"¦"¦.

Will be interesting to hear if anyone else on the forum is experiencing this "¦"¦.. just got this rather funny thought going through my mind with every 911 owner driving around Monday morning listing for this noise, quite amusing really"¦"¦"¦[]


Thank you very much for your suggestion so far "¦"¦.. cheers Mike

 

[mascanes]

ORIGINAL: tscaptain

I'm certainly no expert in this area (or any other for that matter!) but I would have thought that cats breaking up would rattle most of the time. That rev range (around 3200 from memory) is, of course, when the changeover happens inside the engine with the valves/camshafts (variocam) etc.
Sounds like another trip back to the dealer.........[]

Guess what "¦"¦.. I called the OPC after collecting my car the other week and informed them it was still rattling etc and what do we do now. I mentioned the variocam idea of yours. Well, it looks like you might have hit on something. Because the Porsche technician who had been working on the problem said that he thinks it could be the left hand bank variocam solenoid. As you said this solenoid cuts in at about this rpm"¦"¦"¦. They want the car back in for longer this time so they can do "sound clips" and submit them to the Porsche gods for their comments. The technician said it was noisy enough to justify investigating further "¦"¦. More as it happens "¦"¦.

Thanks again "¦"¦. Cheers Mike

 

[tims1959]

Hi,

I'm sure the OPC will get this sorted out for you. Whatever it turns out to be, the warranty ought to cover it.

My 2006 Carrera S does something that seems to match your description - a light/buzzy/tinny rattle between 2800 and 3200 rpm in any gear, but only on very light throttle or gentle overrun.

I've had the car two years now and done 12,000 miles, and the engine's never missed a beat, but from day one of my ownership it's buzzed like this from time to time. My car also has the X51 powerkit, but that's surely just a coincidence.

Although it's probably being triggered by a resonance with some vibration from the engine, to me it's never sounded like an engine noise as such, it's too tizzy for that. It's never sounded annoyingly loud either (my car's a coupe).

So it's never really worried me and I can live with it for now - any excuse to change down a gear, eh?

I can say it's definitely not coming from the exhaust. I fitted an AWE system and that has certainly put a smile on my face, but I still get the exactly the same buzz/rattle as before.

I only ever hear it in dry conditions. In heavy rain or when the road is properly wet it goes away - really goes away, it's not just being masked by other noises.

To me this rules out any loose or dodgy engine internals including the variocam valves and actuators, which live inside the cam covers so wouldn't be affected by wet weather.

I've concluded that in my case it's just the heat shields (between the mufflers and the rear bumper) rattling against each other: I can get a similar sort of noise by tapping my fingertips on the rear bumper from outside the car (above the tailpipes or behind the back wheel). I checked that all my heat shield fixings were all present and tight, but it looks as if the shields warp a bit over time leaving tiny gaps between them, which could generate a tinny rattle.

I know you mentioned that the OPC had looked at the heat shields but it might be worth giving that a try?

Anyway, best of luck, and please let us know how it goes!

Cheers
Tim

 

[mascanes]

Hi Tim "¦.. Sorry I haven't responded earlier to your post. I've just got back off a trip. I left the car with OPC Hatfield while I was away so they could have all the time they needed to try and sort this.

They called me to say they've had another look and done sound clips etc and reported this all back to Porsche head office. Their response is that they are fairly sure it's the X51 inlet manifold. Because, according to Hatfield it is aluminium on the X51 engine and this can cause this effect"¦"¦. Anyway looks like this is all the help I'm going to get from OPC for now. They want to discuss in more detail with me on Monday advising me what they've done.

Funny you said that by banging the lower rear panel caused the same sort of rattle noise. I had the same and they've tightened it all up around this area and banging it doesn't rattle in that area but I've still got the overrun noise.

Thinking of contacting JZM and getting their thoughts on this

Thanks again for taking the time to give me your comments, makes feel better that maybe it is a trait on some X51 engines. Looks like I'm going to be changing down a lot from now on"¦"¦"¦[8D]

Cheers
Mike

 

[okellyt]

Mike

If its a slight fuzzy sound at pretty much bang on 2.9k revs to 3.0k revs and is not too intrusive (it might be annoying because you can hear it) ie not overly loud it is a feature of the x51 and the variable value stuff. If its a loud rattle then I'd get it looked at.

Mine had a slight fuzzy noise at 2.9k/3k revs (x51 also) has reduced significantly since changing exhaust and induction system but with the original aluminum bit in place there is still a very slight fuzz on very small throttle inputs.

 

[tims1959]

Hi Mike,

Thanks for the update, very interesting. I really must learn not to jump to conclusions!

At least this noise is almost certainly nothing bad, even if it turns out there isn't a 'cure', three out of three X51s making similar-sounding noises doesn't sound like a coincidence to me.

It does seem strange that I never hear it in really wet weather - have you noticed anything like that?

I wonder if moist intake air helps (ahem) damp things down

Cheers

Tim

 

[okellyt]

Metal does expand and contract with heat maybe its temperature dependent or maybe the damp air smothers the rattle, but it is much less son mine in the damp also

Curiouser and curiouser

 

[mascanes]

Latest "¦"¦"¦"¦ Went to collect the wee beasty on Monday from OPC Hatfield. They informed me that they were advised by the Porsche gods (assume Reading) to do a complete engine re-map. They said this has been found to dramatically reduce this effect. Guess what? after thrashing it around the A1 and various Hertfordshire side roads......... It's worked[]!!!!

Hatfield said it took two software updates, which they advised is not unusual on a 4 year old car. They reckon that one or more of the software updates could have been related to the cam timing. It's still got the resonance, but it really is just in the background and hardly noticeable.

They had a non X51 Cab in for work and they said it was just noticeable in that vehicle too. They also drove a Boxster around without the engine cover on and said that they could hear a similar sound (god that must have been noisy[]!!) They also said that the X51 engine with the aluminium inlet manifold does sound different "¦"¦"¦

Anyway, I'm happy now !!! [][][]

Thanks for all your inputs and support guys, really appreciate it, I'll buy you all a pint of Mobile 1 when I see you next [8D][8D] "¦"¦. Cheers Mike

 

[tims1959]

Hi Mike,
Thanks for the update - glad it's fixed. My car's booked into Reading for its MOT in a few weeks, I'll ask them to check my ECU and update to newer versions if any are available.

I'll post an update when that's done - meanwhile happy buzz-free motoring!

Hi Tom,
I'm glad yours gets quieter in wet weather, thought I was imagining it.

Hopefully we can all compare notes in person some time soon.

Cheers
Tim

 

[Lancerlot]

I wonder if it's engine detonation "pinking" you are hearing.

This would be certainly be cured by engine remapping ie retarding the ingnition; also in damp conditions due to denser air.

Just a thought. [8|]

Regards,

Clive

 

[tims1959]

Hi Clive,

Hmm - I get your reasoning but this is more of a buzz than a tinkle, and only ever there on really light (or no) throttle at just around 3k, so just not when you'd normally expect to get pinking.

I had a couple of old Mini Coopers back in the 'seventies and got to know the sound of pre-ignition when I accidentally lugged the old A-series engine in fourth gear after flooring it (but forgetting to change down first).

Those were great cars, I really loved them. I had a 1963 Morris Cooper, (997cc, 0-60 in about 15 seconds, 7 inch front brake disks, 10 inch wheels, little rubber cones for suspension), then a '66 Morris Cooper S 1275cc - a properly fast little car in its day, but I spent more getting its bodywork welded up to pass the MOT than it had cost me to buy it.

Enough nostalgia though - knowing the M96/M97 engines' reputation for perhaps not being Porsche's strongest, I use Durametric to help keep tabs on my engine's health, and so far it's never thrown up any fault codes, so hopefully this buzz isn't anything sinister.

But you never know - I had thought it was just rattly heat shields

Congratulations on your new turbo btw: I have fond memories of your Scud going past me as if I was standing still at Llandow a couple of years ago!

Cheers
Tim

 

[garyw]

Tim, I owned (if briefly) and Downton Cooper...[] and enjoying the nostalgia []

garyw

 

[Lancerlot]

Ah Ha,

The dim and distant past........

When I was young and in my prime, I used to autocross a 997 mini. It was actually 2 mins welded together and painted with underseal. [&:]

Was a bit rough and ready but used to win me a bit of silverwear.

Trouble was I always got stopped quite a lot by the local fuzz when on the road.

Regards,

Clive

 

[tims1959]

Thanks Gary - sadly you don't see too many 'real' minis on the road any more. Whenever I do see one I'm amazed at how tiny they are, can't believe I used to chuck one around for fun.

Sorry to go way off topic here, but nostalgia ain't what it used to be and I can't resist sharing a few more late-70s apprentice petrolhead memories (and all brought back because Clive mentioned pinking) ...

- No Chris F to tweak your toes and cambers to within a minute of arc (I'll be up at CG tomorrow afternoon), back then you got a bloke with a bit of string and some mirrors leaning up against the front wheels and a blowtorch and hammer for making adjustments

- No rev limiter or DME over-revs, just yellow I II III on the speedo at the prescribed speeds for first, second, and third gear, then a dose of valve bounce if you still forgot to change up

- No-one asking 'any modifications?' when you renewed the insurance

- No crumple zone or collapsible steering column, just be careful not to crash head-on because if you did you knew you probably wouldn't get a second chance

- A can of WD40 a week on the distributor or the engine would cut out every time you drove through a puddle

- Never take it through a car wash, you knew you'd just end up getting wet (and the engine wouldn't start afterwards)

- Headlights held in place by some carefully-place blobs of Isopon while you saved up £30 for a pair of new wings

- The wonderful smell of old oil, unburnt petrol, and damp felt

- One of your friends could unlock and start you car with his motorbike's ignition key

- Spend hours balancing your twin carbs to get that last elusive fraction of one extra BHP, go for a quick test drive, re-check the carbs and they're more out-of-balance than when you started

- Borrow a mate's Neon strobe to set your ignition timing and you have to wait until nighttime to use it because the light from the strobe is so dim - all for another imaginary fraction of one BHP

- Floor it in second to try and impress your girlfriend after fitting a new LCB manifold, but all that happens is your exhaust falls apart because you forgot to tighten your u-clamps properly

- Dream of owning a Porsche one day