Strange Noise under load! [Archive] - SaabCentral Forums

: Strange Noise under load!


Ianf
7th September 2004, 05:08 AM
Hello All,

I've only had my saab 95 for a few months and may be asking a daft question but here goes.. I've a 1998 2.3t SE with 60k on the clock under load there is what I can only descibe as a big asmatic wheeze from the front of the car like air is being sucked in (it does sound wrong). I've checked (and changed) the air filter to no avail. Is this normal? I sounds this way only when under load and I've never heard this from any car I've ever drove.

Any ideas.

Chris 9-5
7th September 2004, 04:17 PM
Sounds like the Bosch Dump Valve (bypass valve) failing, the diaphram can split and emit strange noises!

Upgraded dumpvales are more reliable and work more responsively but more expensive, if you know another 9-5 owner try swapping the valve to define the noise, its a very easy DIY job!

Ianf
8th September 2004, 02:29 AM
Thanks for that.

I did remove the dump valve and it looks ok to me. What am I looking for?

hildebird
8th September 2004, 08:59 AM
You can't easily see if it is OK or not. If you look up the big pipe which is central on the cylinder (not the one out of the side) you will be able to see (some of) the diaphragm. If this has any cracks splits or holes in it, you need a new one.
To check it, fit a suitable size hose to the small (3mm?) diameter fitting and suck on it while looking up the big central pipe. You should only be able to suck a small amount of air and then no more, and you should see the diaphragm move away from you and open the valve. If you can suck air continuously, the valve is faulty. In this case, you will not see the valve open.
You can also try blowing down the side branch pipe, this should be sealed off unless you are sucking on the small diameter line.

don't forget that all these pipes will be oily and will need a good clean before you put them near your mouth :cheesy:

Ianf
8th September 2004, 09:08 AM
Thanks a lot for that info and for saving me from a mouth full of oil!

I've tried that and it appears to work fine as you described. So if I can rule out that maybe there is a air leak somewhere? I noticed when I removed the dump valve that the pipe that one end connects to seemed lose to me where it joins the bigger pipe before the turbo. I hope I'm making sence! To be clear the pipe that runs parallel to the front of the car from the dump valve that's held in place with a bolt and a clip.

hildebird
8th September 2004, 01:06 PM
It shouldn't really be loose, so try and get the spring clip to grip it a bit better, but that side which connects to the metal cross-pipe is the vent side anyway, so isn't pressurised like the other side.

Also try checking all the small diameter vacuum hoses for leaks, 9-5's seem to have been fitted with some dubious grade rubber hose which perishes and turns to soot. I changed all my 9-5 hoses at about 3 years old and most of them fell apart in removal. At the same time, I changed the hoses on our 12 year old C900 and these were in far better condition.

Chris 9-5
8th September 2004, 02:59 PM
I tried the "sucking" method to test mine but couldnt diagnose it that way. I ended up buying a forge dump valve and changing the vacuum pipes for silicon and the noise completely dissapeared.

Ianf
8th September 2004, 03:30 PM
Thanks for all the tips. I'll get a new valve and fit the new pipes as you suggest. I'll let you know how I get on.

Ianf
12th September 2004, 12:26 PM
Well I've fitted a new valve (saab standard) and it's still the same. I've had a look at all the pipes and they do look ok no signs of cracks. I think it's time to take it back to the saab dealer. :-?

Chris 9-5
12th September 2004, 12:41 PM
Sorry to hear that Ian, I really thought it would be the valve, let us know what the dealer says.

Good luck, Chris