Jump to content

930 odd noise


Recommended Posts

I have an 86 930 with 74k on the clock.  No issues with the way it runs or performs apart from an odd noise that I can't trace.  I get a constant 'middle C' note when the car is under any load.  It's the same note regardless of road speed or gear selection so i don't think it's related to the gearbox, engine internals or diff / drive train.  My mate who is a race car mechanic (ex F1) suggested it may by a split pipe on the induction side, or air value that's not seating properly.  On a trailing throttle or  really light throttle ir goes away, but as soon as any pressure is applied to the pedal (say to go up a slight hill or go into the next gear, it's comes back.  I can't replicate it when the cars is stationary which makes it all the more difficult to track.  It may not be Middle C as I'm tone deaf but that's the best way I can describe!!

Any idea's on how to trace or what it may be.  If I had to estimate the area in the engine compartment where the sound originates, i'd say on the top of the engine, somewhere behind the intercooler if that helps!!

Regards

Mark

Link to post
Share on other sites
13 hours ago, Markmb2 said:

I have an 86 930 with 74k on the clock.  No issues with the way it runs or performs apart from an odd noise that I can't trace.  I get a constant 'middle C' note when the car is under any load.  It's the same note regardless of road speed or gear selection so i don't think it's related to the gearbox, engine internals or diff / drive train.  My mate who is a race car mechanic (ex F1) suggested it may by a split pipe on the induction side, or air value that's not seating properly.  On a trailing throttle or  really light throttle ir goes away, but as soon as any pressure is applied to the pedal (say to go up a slight hill or go into the next gear, it's comes back.  I can't replicate it when the cars is stationary which makes it all the more difficult to track.  It may not be Middle C as I'm tone deaf but that's the best way I can describe!!

Any idea's on how to trace or what it may be.  If I had to estimate the area in the engine compartment where the sound originates, i'd say on the top of the engine, somewhere behind the intercooler if that helps!!

Regards

Mark

Sounds like a boost leak Mark. Common area is where the intercooler presses into the throttle body . There's 2x O rings there . They are prone to splitting. There are a number of other places but I'd check there first as you won't otherwise be able to check unless you're under load. 

D

Link to post
Share on other sites

If it only happens under load then I think a boost leak or, less likely, a vacuum leak is probably the noise. 
 

if a boost leak is significant then the mixture will be rich as air is lost after its metered for fuel. Checking the Air Fuel Ratio (AFR) under load would help if you’re able to do this. Also checking these you’re making full boost lwould be good, although the standard electronic gauge isn’t really accurate. Failing that you need to systematically check all O rings and hoses. As said a common failure point are the O rings at either end of the charge pipe (aluminium pipe jointing turbo to the intercooler) and where the intercooler sits on the throttle body. The bottom. O ring nearest the turbo gets pinched easily. 
 

There are lots of Vacuum hoses in the fuel and ignition systems and also many components that use vacuum (ie have diaphragms - WUR, AAR, distributor etc). Work through checking for splits. Putting components and lines under vacuum using a hand pump is a good way to check and maybe replicate the sound.

Start by removing the intercooler and go from there, checking everything as you go. 
 

David

Link to post
Share on other sites

Thanks for the replies,  I will systematically check and report back.  I need to take the intercooler off anyway as I have to change the seals on the BOV as these click when the throttle is blipped.  Currently waiting for Pelican Parts to deliver.  I don't suppose the two issues are related.

Regards

Mark

Link to post
Share on other sites
1 hour ago, Markmb2 said:

Thanks for the replies,  I will systematically check and report back.  I need to take the intercooler off anyway as I have to change the seals on the BOV as these click when the throttle is blipped.  Currently waiting for Pelican Parts to deliver.  I don't suppose the two issues are related.

Regards

Mark

It’s possible Mark.  I did this a few years ago - the plastic seal disintegrates In the recirc valve. Mine didn’t whistle though, only click on a closing throttle. It’s a good opportunity to check for boost and vac leaks as you say. 
 

Cheers
David 

Link to post
Share on other sites
  • 1 month later...

An update and further question.  I have now received the BOV seals from Pelican Parts (7 weeks!) and taken the intermediate throttle body off so I can replace the BOV seals.  One seal had all but disintegrated and the other was on it's way,  so now have fitted two new seals.  I've not found any spilt pipes or damaged O rings yet but have noticed  a single pipe blocked off with what looks like a pop rivet and jubilee clip. The pipe comes out of what I think is the control valve.  It has been neatly done so didn't know if this is normal, or has been altered at some stage in the car's life.  Hopefully the picture will show which pipe it is, it's the looped one.  Any ideas where this should be attached to or do I just reassemble as is?  I'm assuming there is another end or union that is missing a pipe??

Apart from the strange noise as described above, the car and turbo seems to work fine, I can hear it spin up and the gauge moves to around 0.8 bar when giving it some 'beans'.  I've never heard a Whoosh sound when Turbo waste gate opens so not sure if standard 930's do that.

Thanks

Regards Mark

 

 

IMG_2328.JPG

Link to post
Share on other sites

Hi Mark, 

I think that this valve is a part of the air injection system on a pre 84 930 so I’m guessing that your air pump has been deleted? If so you can leave as-is, or maybe remove the system fully as I have done.  I’m not too sure as my 84 had a different design without that valve, but I think that the hose went to something called a diverter which has probably also been removed.
 

Standard 930’s don’t really make noise when the wastegate opens. On the intake side it’s a closed system with the air recycled through the recirculation valve. On the exhaust side the wastegate vents through the silencer (separate silencer on 84 and later but integral on earlier). You can modify to a BOV and also fit a dump pipe to the wastegate so both air and exhaust go to atmosphere. I run the standard recirc valve but have a dump pipe so you do hear the exhaust as the wastegate opens.

You can’t hear the turbo spool with a standard set up but you can if you run a straight through exhaust (I have a Rarleyl8 using an M&K box). Upside is it spools quicker and builds boost at slightly lower rpm but the downside is that’s it pops and bangs on the overrun and is loud when the wastegate dumps. 
 

Regards

David

Link to post
Share on other sites

Thanks David,

I got the car back together today, finally and took the opportunity to change the fuel filter while the Intercooler was off.  In doing the work on the BOV seals and trying to find why the car makes an odd noise as described earlier, I came across a pipe that was not connected.  It has a banjo fitting on is rubber around 3/8" in diameter.  The unattached end is in front of the metering unit underneath the air filter unit.  I followed the rubber pipe back to a unit that is located on the opposite side (back), but not part of the metering unit.  I don't know what this unit is or if it's the source of the noise.  It can't be fuel as there is no leak, same for oil, so that just leaves air??  The pictures below may help to identify what the unit is...

Regards Mark

 

2F503B8E-C0EA-42CE-ACC8-F4B8DE773697.jpeg

12DAE11E-70E9-4F98-9380-182F9CA953FC.jpeg

0AAD6D65-EA62-43BB-822A-9CC55FE02D9B.jpeg

Link to post
Share on other sites
14 minutes ago, PorscheApostle said:

That' looks like cold start injector. Fuel. 

Yes, looks like your cold start valve, although the picture isn’t that clear. I run with mine disconnected and have no starting issues. I’m not sure all motors will be happy with this; I imagine it depends on fuel pressures, mixture, ambient temperature etc.
 

David 

Link to post
Share on other sites

Yes that's the one, just Google'd and looked at the images.  Thanks.  

The pipe that connects to the top has an open end (disconnected banjo) so I have put a nut / bolt and washers to seal it up.  I've always been surprised at how well my car starts up from cold, even in the winter, even more so now I know the cold start valve has never been connected during my ownership.  

Working on the principle that "if it ain't broke, then don't fix it".... i will leave well alone especially as it's so difficult to get at.  Out of interest, I will research and find out how it's meant to work.

So I have fixed the clicking BOV, just need a dry day to test and see if the whistle noise has gone or changed in any way.

Thanks again for your expert input.

Mark

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...