Turbo/APC guage

Split hose causing hissing noise, maybe bad performance if the leak is big enough, and sluggish response. What problem are you seeing?

Strictly pneumatic, assuming an older 900. No idea about the newer ones. What year/engine please?

The gauge is connected to the inlet manifold via a hose. This can become disconnected either at the gauge (accessible via the speaker grille on the dash) or at the manifold (actually the hose connects to a nylon T, which then connects to the manifold).

The response is fine. Just seems to be that the guage doesn't work. It use to. The car is an 87 900 convertable.

Check the "tee" which is up near the brake servo in the engine compartment, and then when that's not it, remove the left speaker grille in the dashboard top (2 screws), stand on your head, and visualize the fact that the hosee split off of the back of your turbo gage. Easy fix: cut back and re-install. Better fix: replace that hose. Best fix: They're all gonna split, they're 20 years old. Buy a few meters of new vacuum line and redo anything you can see.

Dave

Thank you.... I found the problem.

It's almost certainly a leak in the "air line" or vacuum hose between the dial and the inlet manifold, as Grunff explained.

Alot of C900 pilots, myself included, add another graduated gauge. Up to

1.5 bar (20 psi) should be more than sufficient for most C900 appications, pushing any more than about 1.1 bar on a C900 is rare and not for the feint hearted! The advantage is it allows you to set base boost properly, suggest you google for base boost set up.

You probably just blew the line off the manifold, or as happens with many older C900's the line is perished somewhere. Change all your vacuum lines for silicone and you'll never have to change them again. I got really anal and used blue for vacuum lines and red for the cruise control circuit.

Good luck.

Al

Which end was it?

4 mm ID silicone hose is the best way to replace aging small-bore rubber hose. I've replaced just about all the 4 mm hose in my 1983 turbo c900, and it does improve things when it replaces hose that's cracking and/or splitting and has some leaks.

Craig.

Another thing to look at as well as the hose itself is the fitting where it connects to the manifold. It's common for crankcase vent nipples to not make a good seal as the rubber grommets tend to harden and crack with continually heating and cooling of the engine. The vacuum nipple, while not subjected to quite the same level of heating/cooling as the engine block and cylinder head itself, certainly gets hot and over time the grommet will stop making a proper seal. They're cheap to replace for places like PFS, etc. of any of the other online Saab parts suppliers.

There is probably a better way to do those vacuum connections, and it could well be possible to tap a thread in the grommet hole of the manifold and install some sort of a machined brass fitting onto which the vacuum lines to the brake booster, etc. can attach, but to date I haven't see it attempted. I don't know if the cast aluminium of the intake manifolds on the 8V or 16V engines has enough aluminium cast around the grommet hole to support something threaded into it, but if someone has done this, please let us know!

As an aside I'm still trying to find brass or similar alloy replacements for the high-temp AC cutout swtich t-housing that mounts in the middle of the upper radiator hose in my 8V cars. Do the 16V engines utilise a similarly-mounted thermoswitch mounted in the top radiator hose?

Craig.

yeah, so are you going to share your solution, or just your problems?

This is supposed to be a two way thing here...

Sorry, I'm new to this. It was simply a small vacuum hose at the T connection that was mentioned to me.

Ah, good. Thanks for the follow-up report. ;-)