Installing Brew City Boost Bypass Valve (BPV) in SAAB c900

My trusty c900 convertible, Greeny, has had some annoying driveability issues since her conversion to Trionic 5 (aka T5) engine management a couple years ago. Mainly occasional uneven 'hunting' idle, but sometimes just dying entirely. Not all the time, but sometimes, which is frustrating to track down.

It sure feels like a vacuum leak. I went through and replaced all the old vacuum lines with silicone and recently relocated the MAP (manifold air pressure) sensor much closer to the intake. All of this made for major improvement but still I had the occasional issue which I wanted to resolve. Aside from the sometime annoyance, life with T5 is fabulous, what with 18 psi of boost (!) and much better throttle response. When the boost comes on, hang onto your hat!

One thing I had not done was replace the old Bosch turbocharger bypass valve (BPV). I read where a sticky or failing BPV could result in the type of thing I was seeing, especially the odd just dying sometimes instead of coming back to idle. The purpose of the BPV is to dump boost pressure away from the intake when the throttle valve is shut - the pressure would otherwise have nowhere to go, so the BPV allows it to exit from the intake. If the BPV is leaking or sticky, it can create driveability issues.

With all that in mind, I set about installing a new BPV. I didn't want to just replace the factory BPV with the same thing, since it's plastic and notorious for sticking. I briefly considered the GFB valve, but $200 was a bit pricey. In searching around, I found Brew City boost and their 'knockoff' BPV.

BCB markets their BPV for NG900s, 9000s, 9-3s, etc. There is no mention of a c900. But the BPV is the same, it's just in a different place.

Surely it will work...bwhahahahahha.

This is not a difficult job - you just need to make note of how the pipes, connectors and vacuum lines are connected. Take pictures or make drawings to ensure it all goes back the same way.

You can see the BPV is a bit buried under the pressure and intake pipes. We just need to remove them to get at it.

My (gloved) hand is on the pressure (silver) and intake (black) pipes.

We undo the clamp on off the turbo's compressor side.  Put a clean towel in the outlet after you get the hose off so you don't drop anything down there!

Undo the other end of the pipe where it connects to the intercooler.

Here's the pressure pipe removed.

Note that depending on the ease of access and tightness of the clamp fittings, I used a nut driver, a socket, or a screwdriver to undo the clamps as I went along.

There are vacuum lines running from the boost control valve to the turbo, the turbo's blowoff value (not the BPV) and the intake pipe. You'll need to undo a couple of these for the pipes to clear.

Note that this valve is part of the T5 system. Mine is mounted on the panel above the radiator. Stock 900s don't have this.

More undoing of clamps - here's one end of the intake pipe. This is the airbox end.

The turbo end is more recessed but can be reached with a socket and long-ish extension.

I found it easier to disconnect the factory connector to the airbox to help maneuver the pipe off the car.

The connectors just spring off the airbox.

One connector that's a bit of a pain is the connector that joins the crankcase breather line - it's steel - into the intake pipe. I used a screwdriver to wedge the connector off.

The breather pipe fits into a rubber donut on the intake pipe.

Here it is removed. You can see the pointed end of the breather line and the donut on the pipe. The pipe is pretty much free at this point - I've rotated it a bit for this picture to show the two pieces that fit together.

You can now pull the intake pipe upward, with the BPV still attached.  The clamp on the BPV needs to be loosened - the other end of that smaller hose on the BPV goes up to the intake manifold.

Here I've loosened the BPV clamp - and moved the intake pipe along with the BPV upward to remove from the car.

I also have removed the end of the BPV's vacuum line. That line connects up near the intake manifold, where it joins two other lines (I show that connection further down).

Here's the intake pipe along with the BPV removed.

Funny how these wide angle camera shots (I think this is about 28mm focal length here) make the pipe look as big as the engine!

Comparison between the shiny new Brew City Boost BPV and the stock one.

The new valve comes with 3 different springs - light, medium and stiff and is rebuildable. Really a nicely made piece. Too bad nobody will see it after it's installed.

I have the stock (light) spring in for now.

A shot of the internals showing how nicely made the BCB valve is made. 

Installing the new valve is a reverse of what we did to get the old one out.

Put the new valve on the intake pipe. I didn't tighten the clamp down all the way so I could move the valve as needed when locating it.

Here it is tucked into place.

Note the vacuum nipple on the turbo - that's for one of the lines that goes to the boost control valve.

Another shot of the new valve in place - with both of those vacuum lines connected. At this point I tightened the clamps on this end.

Reconnecting the breather line to the intake pipe. We're looking at this connection from the airbox side of the engine.

This connection was frustrating. The donut is really tight on both the steel line and the intake pipe. The intake pipe is plastic, so it wants to flex under pressure. I wound up popping the donut out of the pipe, slipping it over the breather line, and then into the intake pipe. 

Another angle on the turbo end of the intake pipe. The BPV is just visible in there.

Tightening up the clamp on the boost pipe.

Here's where the BPV connects at the intake manifold. It's at the same point where the MAP sensor (part of the T5 conversion) connects.

At first, I had the MAP sensor was on the other side of the engine compartment, but I relocated it to keep its line as short as possible.

Everything is back together.

The car is running much better, much less fluctuating idle. It's not dying when returning to idle from high speed, so that's an improvement. And the car seems to build up boost a bit faster than before.

I'm planning to replace all the old rubber intake lines with silicone ones from Do88 - that's the next project.