Bitsa

Thanks Guys

I'm feeling better about it now that I've seen some more "technical" explanations for the problem...

I wish my dealer could give me the same "detailed" ,"technical" reasons for the problem... even if they just relayed the info from Porsche ! But even the Porche Rep didn't have any explanation to offer (according to the service guys at the dealership) !

Hey CARERRA GT ! Are you a Porsche Dealer ?
.

TD in DC

Carrerra GT,

You are absolutely correct that you get the same sound if you shut off a hot engine and immediately try to restart. I rarely (or never) have the problem when cold, but hear it when I restart.

TD in DC

Carrera GT

Dealer?
No, I have a little Porsche service shop near San Francisco ... spark plugs, oil filters ... you know, the usual stuff ... Ohlins, JRZ, Brembo, Recaro, Forgeline ...

Lagavulin

A couple of weeks ago when I saw a black 997 S in person, I was standing outside in front of the car when it was cranked up, and it sounded just like a popcorn popper (..literally)! I was very surprised as I have never heard that type of staccato from an engine before.

nyca

interesting, so you are saying its part of the LEV compliance? I can understand this when the car is cold (cat is cold). but what about the people saying they get the same noise on a restart of a hot engine? do they just run the pump by default until they can get a reading from the O2 sensor that shows the cat (hot in this example) is actually working?

Ray G

Yes, corn popper is what I hear with my 997S on cold starts. My kids even asked me "are you popping corn?" when they heard it.

ScottS

Funny, the sound you're describing sounds more like 997 resale value dropping down 20%.

nyca

the current Car and Driver has a blurb on the new 997 motor in the "2005 new cars" section - they don't mention this noise specifically, but they do mention the air pump mechanism referred to here needed to meet emission standards. but one would think they would have spotted a problem like this, and been more attentive to solving it.

nyca

article below, read down to the "Technical Highlight" section:

http://www.caranddriver.com/article....rticle_id=8608

"To comply with ever-tightening emissions regulations, there's a pump to inject air into the exhaust manifolds during cold starts. Combined with a richer mixture and retarded spark timing, this injected air causes the catalyst to light off more quickly. But the system requires a camshaft-driven vacuum pump to compensate for the loss of engine vacuum during this cold-start procedure."

the mixture and timing change adds to the "noise" I would think - these stupid emissions regulations that require this, aren't they satisfied enough to have the car not pollute after it has had a few minutes to warm up?

Bitsa

Thanks NYCA !

The "Air Pump" explanation seem to fit my problem !

Now, if only the Porsche Rep had known about it :-o

I've sent an email to the Service rep at Rusnak and asked him to explain it to the PCNA rep..

nyca

Yes, send it to the service and PCNA reps - they certainly should be better informed and more helpful to you.

Ray G

Yesterday I listened carefully to the sound on cold-start. I think it really is nothing to be concerned with. The sound is not coming from inside the engine - it is coming from out of the exhaust. I'm sure it is just the engine running rich with extra air pump etc to heat up the cats. It goes away after a minute. It only happens on cold starts. -Ray

SkipSauls

Have you guys opened the engine cover yet? I did and it's pretty clear where the noise is coming from:



It's an air popper, so the popcorn is pretty bland by itself, but there is a handy butter compartment on the top. It's been a while since I've had air popped corn, and I've forgotten how good it is compared to the microwave stuff that's so common today. If you don't eat the popcorn, it falls down into a rotating blade driven by the fan belt where it is all but vaporized and released into the air stream behind the car. Oddly, you won't have to fill the popper that often because there is a huge amount of corn stored behind the rear seats. I was wondering what was in the area that was an indentation on the 996, but this explains it.

csertich

chuck

PrimeArchitect

Hi all

I just had the cylinders 4-6 replaced on my 2006 997 C4S as they had scratches after 70K miles. when I got the car back I notice that whenever it's idling now the engine emits a rattling sound. Seems to come and go in the sense that it gets louder and quieter but I'm not sure I've quite identified the circumstances fully. Definitely rattles loudly at start up when the engine is cold, so I suspect the oil getting warmed up is part of the reason it gets quieter but it's not going away completely.

Normally I'd just take it back to the garage that did the work but they've worked on the car three times (under warranty) and each time the original problem gets solved the car comes back with a new problem, and this is a case in point. Got the cylinders replaced but now I've got the engine rattling like crazy every time I stop at traffic lights, loud enough to have everyone walking by wondering what the noise is.

anyone got any ideas on what the problem is?

here's a video of the sound

https://*******/bfh

Thanks