348 question

It very could be, and probably is, a bearing problem.

I recently had a whistling noise and the problem turned out to be (thank God) only an alternator belt bearing.

Please see my thread here regarding this issue.
http://ferrarichat.com/forum/showthread.php?t=94943

 

I didn't see much in the archives beside this: http://www.ferrarichat.com/forum/showthread.php?t=76491

and a few references to the 348's emmission controls and exhaust tips...

at least, other than "bearings."

I can say though that the 348 does something unique from 3500 to 5500 rpms; we've got Intake Compensation Solenoid Valves. The ICSV is activated between 3500 and 5500 RPM's (when we are at Wide Open Throttle (WOT). This improves torque by opening our Compensation Throttles (helmholtz resonators).

Our transmissions do occassionally whine, either from bearing failure or from a simple linkage misadjustment (testable if the whine goes away when you put pressure on your stick shift): http://www.ferrarichat.com/forum/showthread.php?t=80586

 

How does our air pump emmissions work? Do they shut off at Wide Open Throttle?

Also, would a bearing make a noise at half-throttle that it wouldn't make at full throttle?

 

So which part is the ICSV??
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

My 348GTS sometimes whistles. It's a very subtle whisle and is 100% like a turbo whine and occurs under the exact same conditions i.e. accelerating moderately under load, perhaps in a higher gear than you should have selected.

It doesn't sound at all malevolent and the dealer seems to think it's just a normal noise from the induction.

To be honest, it sounds quite pleasant, and certainly nothing like a failing bearing.

 

Well from this description it sound like something to do with the intake compensation valve. It's located under the front bottom part of the intake plenum. You could either have the leaking air tube, or the vacume tube could have come off. If you look at the first picture that ND posted the tube is #14. The valve opens at the rpm's you are describing to help balance the intake pressure inside the plenum. It is run off of the 5/8 engine ecu. So when the rpm's are between 3,500 and 5,500 it opens. What I'm thinking is the "whistling" you are hearing is the tube not making contact with the intake compensation valve, or it could have com off of the intake compesation solenoid. So instead of the valve being opened, all you are hearing is the air being sucked into the tube. Go have a look at ALL of your a vacume tubing, make sure everything is connected and the tubing is in good condition.

 

Hey Ernie, for us dillettantes rather than the pros, can you explain how Dr.T or myself could disconnect the ICSV signal?

I'm thinking that the tubing might be difficult to verify as being connected...but that if the ICSV signal is disconnected that he can test to see if the whistle goes away.

Perhaps that would isolate his problem?

 

The tubing is not hard to verify. All you have to do is look at all the connections. I DO NOT recomend that you disconnect the Intake Solenoid. The solendoid is there to help with the power of the car under acceleration. Also if you were to disconnect it you wouldn't be able to hear where the whistling is coming from. It sound like the problem is with the vacume tubing not the solenoid, because he is hearing the whistle, and thus there is vacume going on and the solenoid is functioning. But if you want to disconnect it all you have to do is unplug it. Looking in from the back of the car the solenoid is on the bottom lef side of the plenum, to the left of the oil filter. Again I would leave it connected and try to find the tube that is not connected properly or is leaking. So start at the solenoid and work your way around the tubes. You could have the engine running and then rev the engine to 4,000rpm or so. Listen to hear if the whistling is coming from the solenoid, or from under the plenum.

 

The solenoid opens to help with the midrange torque, not that the 348 has a whole bunch of torque to begin with. So If you are running without the compensation valve functioning properly you won't accelerate as quickly as you could in the mid rpm range. The solenoid is not open at all times, only between the given rpm's. So when you are just putting around town at 2,800 rpm it is closed, or when the engine is singing at 6,800 rpm it is also closed. It is only to help with the midrange torque of the engine, by varying the intake flow, and opening bewteen 3,500 - 5,500/rpm. So if it isn't fuctioning properly the compesation valve isn't being opened, and thus cannot open the throttle inside the plenum to vary the pressure between the to side of the intake.

I don't think your solendoid is bad because you are hearing the whistling. If the solenoid was bad you wouldn't hear anything at all. The solenoid opens and allows the air to be sucked through the vacume tubes. If there is no problem with the with the conditions or connection of the tube you should not hear any whistling because the vacume would be opening the compensation valve and not making the whistle. Again I do think it is a problem with the vacume tube because you are hearing a whistle, meaning that the solenoid is opening and closing as it should.

But then again I could be wrong and it could be the boogers in your nose doing all the whistling because you were breathing so hard from all the excitment. LOL

 

It should be fine to disconnect the ICSV for a test. All in the world that it does is to tune the sound (helmholtz resonation means matching sound wave pulses to when the intake valves are open) and equalize pressure between plenums. Without that fine-tuning you will lose some mid-range torque...but that should be fine for a test.

If the ICSV is disconnected and you no longer hear the whistling, then surely Ernie is right that it is an ICSV connection problem.

 

No

I said I thought it could be a vacume tube problem.

 

My mistake. Sorry.

 

Nope just go to the auto parts store and get what you need. "Sounds" like the rubber is dried out. They sell the stuff by the foot. Take one of the old tubes to match it up with the new stuff. While your at it I would go ahead and change all the old vacume tubing.

 

Say, did you try reving the engine while it was on, so you could listen to where the whistling was coming from? If you haven't I would give that a shot.

 

I'd think that DrT still needs to isolate the problem. His problem exists at partial throttle between 3,500rpms and 5,000rpms, but goes away at full throttle.

This could be the air injection (e.g. a hole in an air line), which probably shuts off at full throttle and might not be very loud below 3,500 rpms.

Or somewhere in the ICSV system (very coincidental rpms).

And that's if it's an air whistle rather than a bearing whine.

 

Dr.T, any updates?

 

My car does the exact same thing. I had it checked out and the mechanic cited the air filter (a KN type) as the result. We chased it for some time and this was the result. We did not replace the air filter, however, so there is an outside chance that there is another cause.

The car makes the noise only under load, so you cannot duplicate it under idle by revving the engine. Worse, you can only hear it from the driver's side of the car, so it may be the issue is located on that side of the engine bay. I have stopped chasing the noise, but I sure would like to find the cause if it is fixable. The fact that it occurs only under load leads me to believe that torque may be related, as ernie says. I'm keeping an eye on this thread.

BTW, my Spider never did this and it only had the stock air filter.

 

BTW, my mechanic discounted that vacuum could be the cause since the whistle sounds only on near full throttle at that 3500-5000 rpm speed. He claims that there is no engine vacuum to leak.