1995 Saab 900SE Turbo Bypass Valve location??

OK, so I finally figured out where the bypass valve was. When he said it was disconnected he was apparently talking about the small "baby" hose that comes out of the top of the valve, not the whole valve itself.

I looked around the engine compartment and there is a small diameter pipe coming out of the right front of the turbo (as you're facing the front of the car) which doesn't have a hose connected to it. Is that where its supposed to be connected?

Robert

The vacuum line to the Turbo Bypass valve is disconnected and the engine doesn't stall when you take your foot off the accelerator to stop? That doesn't seem possible. And the hose is not just held on by vacuum; it should resist being pulled off unless the hose is worn/stretched/cracked. If that is the problem, cutting off the damaged part (which should only be a short amount) should resolve the problem long enough to see if there is an improvement. The vacuum hose on my 1991 9000T doesn't yet show any of these signs, although the valve itself failed and needed replacement.

That little hose is just a vent to the atmosphere and doesn't go anywhere.

The small hose from the front of the turbo goes to the top (c) input on the boost control solenoid (apc)

Here's some pics that will help you out.

Frank /~

in article snipped-for-privacy@q75g2000hsh.googlegroups.com, robertjm at snipped-for-privacy@hockeyhockeyhockey.com wrote on 14/04/2007 23:37:

The breather hose does have to be a specific type with a proper oil resistant lining. Air/oil mist that comes off the crankcase can attack normal rubber.

I'm not exactly sure, but if you follow all the hoses off your throttle body (should be one between 15mm and 25mm), you'll arrive at it in the end. It's black, says Bosch on it and on your car should have two large 25mm ports and one vacuum port. It should fit into the large air pipe that runs between the airbox and the turbocharger.

With regard to your vacuum, hose is cheap enough to replace all the hoses under the bonnet. Take each one off in turn, cut the correct length from your new reel and fit it. Don't think about pulling them all off first, or you'll forget how they go back together.

Paul

in article snipped-for-privacy@4ax.com, Frank Vuotto at snipped-for-privacy@hotmail.com wrote on 15/04/2007 05:18:

This is not actually right.

On a re-circulating valve like you will have on your model, the smaller hose is an integral part of the valve's working. A run of vacuum hose should run from that port up to the intake manifold. Check all the small (4mm) hoses that run off the intake manifold and see if any are not connected. A vac leak will lead to a high idle, poor running and increased fuel consumption, not to mention the car stalling. Some cars can compensate quite well, but best find the errant hose and re-connect it.

Contrary to popular belief, the boost pressure is not the main force acting on the valve to "force it open". The vacuum line is the force that actually pulls the bung inside the valve. You can prove this by turning the valve around and putting it on the other way ... It will still work. In fact, on the later 9-3 Viggen model, the valve is actually fitted from the factory "the wrong way round".

Take a look at this link:

Aside from being a good resource for comparing popular market diverter valves, it shows in the table how the valves are best orientated. Notice the standard Bosch valve is best orientated "normally".

How to fit in reverse:

So ... You must have that vacuum line connected for the valve to work.

Yup! That's the charge hose ( C ). You can follow the bottom picture to test your solenoid valve, not that we suspect anything wrong with it at the moment.

Paul

in article snipped-for-privacy@w1g2000hsg.googlegroups.com, robertjm at snipped-for-privacy@hockeyhockeyhockey.com wrote on 15/04/2007 06:13:

It's likely that an unconnected vac hose is compensated for by the engine management by giving more fuelling. In certain circumstances, like when coming off boost, the engine may go very rich. You may end up with your "Check Engine Light" (CEL) coming on ... Unless a previous owner pulled the bulb?

Just connect up the vac hose as I described earlier and you'll be fine. Don't go blowing flames at the chap at the smog shop - he'll laugh at you :)

Paul

If this is a '95 NG900 turbo, there should be only one hose coming out of the bypass valve. It leads back to the manifold, as Paul suggested.

See this diagram:

These hoses are known for becoming brittle and often breaking off. Most of us with NG900's have purchased 6 feet or so of hose and replaced (one by one when we do it) all the (small) vacuum hoses on the engine. Total cost is about $5 and it takes at most a half hour.

in article snipped-for-privacy@4ax.com, still me at snipped-for-privacy@yahoo.com wrote on 15/04/2007 16:07:

That's an excellent diagram - well played! Yes, indeed ... I believe it is port #4 off the throttle body.

Paul

True, it really needs the small tube to work.

This is how it's placed in our '95 900SE;

in article f05mka$6ho$ snipped-for-privacy@news6.zwoll.ov.home.nl, MH at snipped-for-privacy@no.no wrote on

That is in what is called the "correct" orientation. Notice how the valve is orientated so the internal bung and spring actuate perpendicular to the charge air. The smaller vac hose rapidly sucks the top of the valve when the pressure drops out of boost.

On some later SAABs (and other turbo cars), the valve is placed the other way around, so the charge air cannot technically act upon the underside of the internal bung. The valve is purely actuated by vacuum.

Paul

in article C24D8CDC.827F% snipped-for-privacy@blueyonder.co.uk, Paul Halliday at snipped-for-privacy@blueyonder.co.uk wrote on 19/04/2007 21:17:

Duh! Forgot to attach the pictures :)

Like this:

... Or this:

Paul