Hissing from Rear Turbo or Intercooler???

[spec1976]

Hi Folks,

I am seriously peed off with my Noble at the moment. Hope you guys can give some advice?

Ok i broke down on Good Friday due to alternator problem and it didnt charge the battery. Was able to get home with assistance from some nice passers by who gave me multiple quick charges. I replaced the alternator and that seems to be fixed now.

Anyway after starting the car i notice that the boost gauge is reading -0.5 at idle. This was not like this before as it used to sit at maybe -0.2. After leaving the car to get to temperature and double check the alternator the boost gauge is still at -0.5. On revving the car it will go up around 0.0.

When i turn off the car i hear a hissing sound that goes on for about 15 seconds. this is at the back and sounds like it is coming from the intercooler or rear turbo. I cant seem to hear the hissing when the car is idling but of course it is loud. I checked the hoses to the turbo and cannot find any air escaping.. What i did notice is the lambda sensor wire does seem to be twisted at a right angle. I cant see for sure if it is broken.

Some mods I have done recently in the last couple of weeks, I installed the Pro ally oil separator & Header tank.

Any ideas what could be up, Lambda issue, a leak elsewhere, turbo screwed, coolant (cant see any leaks, wrong install with my mods. I havent been out in the car to see if i am down in power or anything yet, should I?

I am so fed up

Thanks

Steven

[Adrian W]

Check high pressure pipe work again, including intercooler, if it's hissing you must be able to find the source of the noise.
The rear turbo to intercooler pipe is a weak point, they split.

[coolchris]

my intercooler had a huge split in it Dave at jetstream found the problem but it was not visible as it was down one of the seam welds hidden behind its boxing.Check large intake pipe as well mine was loose simple push fully back on then clip tightened up and it was ok.

[Green3R]

Hissing noise for 15 seconds after you turn it off...

Not a clear answer, but my thinking would be;
I can't see there would be residual presure in the intake so that would rule out boost pipes.

You'd smell a coolant leak I think- and you'd notice a drop is the water level (check when cold).

Could the fuel pump still be running? (can't see how).

Turbos / bearings running down is my best guess. If they've become noisy then that might indicate wear? A kinked oil line?

Would you be able to say for sure that the noise wasn't always there? ie you're hearing it now as you're testing with the clam open and an ear that's alert to trouble?

[stevegto3]

When you say 'hiss' do you mean it sounds like the car does a outward breath (if that makes sense) immediately after ignition goes off?

If so mine has always done this, I thought it was just the air pressure in the system escaping from the filters. however it goes after a second.

[StreetDragster]

If you get a length of vacuum pipe, stick one end in your ear, and use the other end to listen to points round the engine it sould help you locate the hissing.

[TuxMan]

all sounds pretty normal to me , suggest you go and have a drive too see how it feels .

[Blu3R]

Your boost gauge readings at idle and when revved with no load are exactly how it should be. If you were at -0.2 on idle before then I'd say there was something wrong then but not now. -0.5 is about perfect.

[Green3R]

I'm gonna pop out in the garage later and see if mine hisses. Probably does and I've never paid attention before!

[Hollowpockets]

TuxMan said:

all sounds pretty normal to me , suggest you go and have a drive too see how it feels .

Exactly, there's nothing wrong with the car, the problem is your paranoia. (I still get this)

They all sit in the -0.5 and it did do it before, you just never looked properly. You rev it then it will climb to 0 and only once under load in gear will it go into the positive.

Hissing after the car turns off? that's most likely the noise of your turbo's still spinning down to a stop. Drive the car and tell us what pressure the gauge gets to on full throttle. At worse you'll have a loose clip or a burst rubber hose but you won't hear that when the car is turned off

Graham

[spec1976]

Thanks for the comments, I will take it for a pin tonight and see if there is any loss of power.

Unfortunately the hissing sound was definitely not there before