Ian964

Just today I started to hear a high pitched whirl sound coming from my car. Its coming from behind on the drivers side. I first though something might be rubbing but then I turned the car on but didn't start the engine and I still got it at random times. It wasn't bad at all just a few times.

I just took it out and now its happening like every 10 seconds, and it can last for 30-40 seconds, its VERY iratating.

I'm thinking its gotta be something to do with the sterreo? I tried getting in the back seat but I couldn't get it to do the sound again.

Any idea?

Mr Michael B

Could very well be your air pump or air pump belt.

I had an air pump belt going bad on my 1991 and it did what your are experiencing.

The pump is located right there (behind the drivers seat - in engine bay of course).

Ian964

Would the air pump be working without the engine on? I can hear the sound just with the electric things on (key turned 1 notch).

Mr Michael B

Oh man...

No, the air pump in your car is driven via a belt off the cam...

A 993 has an electric air pump that fires up off the key...

I have the fix for you though... Turn up the radio & forget it. <img border="0" title="" alt="[Wink]" src="wink.gif" />

Maybe your just hearing a fuel pump cycle.

Ian964

I tried that, and its so high pitched that you can't really just tune it out. Its really bad.

Adrian

Dear Ian,
Check under the right hand seat and see if the noise is coming from the radio booster. If you think the noise is in the engine I would be looking at the ignition transformer (coil) these things can really hum just before they go pop!!!
Ciao,
Adrian
911C4

Ian964

Adrian, if it goes pop would it do a lot of dammage? Should I take it in to be looked at?

special tool

Hey Ian - have Toby come up from Ct. and give it a listen. I am sure we can figure it out.
<img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

Ian964

I was driving my car today and I was driving pretty hard on from an onramp onto the highway. I was at about 5000-6000 rpms and Instead of shifting from 3rd to 4th I shifted down into 2nd(not on purpose) for like maybe ... 1/4-1/2 of a second. I didn't fully release the clutch and I poped it right back into N and slowed down. The neddle definatley readlined and for a second. Could I have done some dammage? The car isn't running any different.

PeterV

Ian,
normaly most engines are protected from over-revving either by ignition or fuel cutoff, sometimes both, so under the condition when the engine is driving the back wheels, the engine will not be allowed to over-rev.

In your case it is the opposite, in that when you shifted into second, the momentum of the car caused the back wheels to force the engine to rev harder, rendering any safety devices such as fuel/ignition cut-out ineffective.

Given the right conditions [like going down a steep embankment] one could for a short instant force the engine to reach any rpm!

Have you caused any damage? Who knows, probably not if the engine did not go too far over the redline. In any case the reality is if you have caused some minor damage, what are you prepared to do about it? Take the engine down and inspect the internals?

If the engine sounds and goes the same as before without any unusual noises, then thank god, leave well alone and relax.

peter
93 Turbo 3.6

Adrian

Dear Ian,
The 964 Turbo does not have a built in rev limiter. It has a boost limit circuit. If you hit redline you will not damage the engine or the transmission. They are built to be driven at redline. It is how far over redline that can sometimes become a concern.
I very much doubt that you have damaged anything. You would hear it and feel it by now. Expensive mechanical rattles and grinds. Redline clears the gunk out of the engine.
Ciao,
Adrian
911C4

Kevin Ross

Ian,

I could be way off here, but I had a similar experience in my C4, it turned out to be Aircon Clutch giving in....

Ian964

Aircon clutch? What is that.

I took the car out today and it did it when I first started the car for about 40 seconds. Then it stoped and it did it once more about 5 minutes later and thats it.

Its not the speaker, I checked that.

fc-racer

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Adrian:
<strong>Dear Ian,
The 964 Turbo does not have a built in rev limiter. It has a boost limit circuit.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Actually, this is inaccurate. The 964 Turbo definitely has a rev limiter which shuts off the fuel pumps when you reach ~6800rpm. It is the MOST violent rev-limiter I have ever felt in a car. It essentially shuts the car off for a second. I'm scared when I'm driving hard on slick services if the wheels spin and it hits the limiter.

This limiter only comes into effect when you are accelerating. On a downshift, it will not prevent over-revving.

fc-racer

Adrian

Dear FC-Racer,
You are quite correct. The Turbo does have an engine governing feature. I have no idea where my mind was but it was certainly not on the job when I wrote my answer.
The violence is because the ground to the fuel pump is removed at 6,800 rpm which in a CIS system is not appreciated.
Ciao,
Adrian
911C4