Dr_KarlB

I hear a similar metallic rattle sometimes... especially if i blip the throttle when downshifting and the revs are quite low.
Again CA Bay area gas :-)

Hella-Buggin'

I've gotten that exact sound under the exact described conditions. It always happened on the same corner coming up the hill on my way home. I just started going down into first to keep the rpms up and try and stay out of that lower range when possible.

Skibum

It still happens to me even if I run 100 octane gas.
As so many folks have the issue I guess it's OK?

Sharkys

Been lurking for a while, but I just had to register to contribute information on this topic. I hear a faint 'ping' when I used to practice heel and toe on the street. I gave up practicing because the speeds were so low entering a corner that the brake and accelerator peddle were too far apart to effectively practice. In the corner, the RPMs would drop more than necessary and a moderate to hard stab of the gas peddle to match at the low rpm would cause a single ping. Imagine a really lazy shift with some right foot action to bump RPMs. I added a few gallons of racing fuel and I never heard the ping on the same corner or under similar circumstances but I can't say 100% that the 100 octane gas I mixed (50/50) with 91 Octane Chevron Techron resolved the issue. I never hear the ping when I'm 'on it'.

Skibum

Would be great to get an official word on this...
I wince each time it happens.

Macster

Uh, they told you wrong.

The knock sensors detect pre-detonation vibrations and the engine controller retards the timing. The intent is to avoid any detonation, not stop it once it appears.

If one hears detonation its over. And sometimes detonation is not audible. Just the sound of a breaking engine.

Sincerely,

Macster.

Macster

You're doing the right thing.

The easy solution is to just avoid subjecting the engine to the operating conditions that cause the noise.

The symptom everyone's talking about arises from the lean air/fuel mixture these engines experience at low engine speeds and when the throttle is opened suddenly.

Opening the throttle a bit too much when the engine's operating in its lower rpm range results in poor combustion to the point we can hear it.

Opening the throttle causes the intakeair speed drop to slow some and this lets some gas fall out of hte intake air stream so the mixture is momentarily leaner than it is at other times.

Porsche could 'fix' this by elecronically limiting the rate at which it allowed the throttle valve to open (it almost certainly does this to some extent already) but the car's responsiveness at higher engine operating speeds might be affected then everyone would complain about that.

These engines are high performance engines and while they do work well at lower engine speeds they're not truck engines. Give 'em some rpms people.

No need to go all crazy and bounce the tach needle off the limiter every upshift but just try to keep the rpms up in the higher gears.

My Boxster will not make this noise no matter how low of rpms I drive the thing at, even at 1K in 4th. But the Turbo doesn't like low rpms and I keep the rpms up higher when I drive the Turbo vs. when I drive the Boxster and the Turbo engine loves me for it. And I love it right back.

Sincerely,

Macster.

cbzzoom

Hmm.. someone tell me if I have this right -

the ECU advances timing under decelleration/coasting to reduce emissions

thus the worst ping would happen when you are coasting at low rpm with foot off the gas, and then apply throttle hard.

I think I have this.

I think there was another thread about the same thing :

http://www.6speedonline.com/forums/9...gine-ping.html

Fahrer

No...
The ECU advances timing under light throttle to increase efficiency. Pinging cannot occur when coasting because there is no fuel being injected at that point. When someone steps on the gas, the ignition timing is retarded to prevent pinging. But with these cars it does not seem to work so well.

wwest

When I picked up my '01 C4 at the factory I was told that I would not always be able to find premium grade fuel in our travels in europe but not to worry the car would automatically address adjust the A/F mixture to accomodate low grade fueling. When I asked, the factory rep told me that the engine control ECU continuously monitors the knock sensor in relation to crank position. If the knock/ping occurs post ignition then the timing is retarded, if the knock/ping is pre-ignition then the mixture is enriched slightly.

So the ECU learns, in real time, the proper timing and A/F mixture "on the fly".

To do that it must CONTINUOUSLY run "trials", pushing the envelope as it were, trying to attain the most AGGRESSIVE settings/parameters for both. With that single "ping" just as the engine transitions from 14.7:1 standard (idle/cruise) mixture (oxygen sensor controlled) to enriched (~12:1) mixture (MAF/IAT controlled) the engine ECU "learns" what A/F mixture ratio to use.

I would be surprised if the knock/ping were encountered more than once per drive cycle.