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· Deez Nutz
22,085 Posts
Discussion Starter · #1 · (Edited)
This is how to install a boost gauge into your 9-3 saab. Please read all of the way through first, and determine what supplies you will need.

So, you have a 1999 Viggen, or a 2000+ 9-3 with a turbo. That means you have T-7 engine management, are a responsible type, and you would like to install a boost gauge before you do any engine modifications.

That's great!

Not only is your boost gauge fun to watch, it's also a useful diagnostic tool!

Our fine swedish cars are vulnerable to vacuum leaks, and boost leaks. A boost gauge can tell you these things!


Click here, and read up:

Now you are thinking "ok e-jerk, how is this useful?"

Well, it's easy.

If you have a car that reads 18 on the vacuum side of the gauge (that you installed thanks to this guide) all the time at idle, and all of the sudden you start it up one morning and, oh shit, it reads 14, you have a vacuum leak.

That means the engine is getting non-regulated air from somewhere else outside the "intake stream", and that's bad. That can mean a crappy idle, poor gas mileage, and a BOOST leak.

A boost leak sucks, because it makes your car slow.

All of the fun pressure that the turbo is making is leaking out some rubber hose, and stealing all of your frumroll (insert brand here) crushing fun.

A boost gauge tells you if you have a leak because all of the sudden the peak boost you brag to your friends about (12 PSI peak stock, yo) is at 9 PSI.

Your Saab factory dashboard boost gauge that you thought was really freaking cool until now, will not tell you these things/. It reads AIRFLOW, not actual BOOST PRESSURE. These are very different things.

So, here is how to put a boost gauge into your T-7 saab:

First, you need to find the proper vacuum line to tap into. Tapping into the proper location is important.

Your first instinct may be to tap into the line on the ByPassValve. The ByPassValve is like a blow off valve that sucks. Instead of making a neato "PSSSHT" noise that all the cool people with turboz make when they let off the gas, it simply ventilates the leftover boost pressure between the throttle plate and the turbo itself back into the intake, and does not make much of noise.


Before you ask...

You CANNOT have a BlowOffValve on T-7 because T-7 "reads and needs" all the air that passes through the motor. If some of the leftover air goes out a BOV for the "PSSHT" noise T-7 will miss this. It's called "metered air". If there is too little "metered air", T-7 will freak out, and give you a CHECK ENGINE LIGHT.

Here is a good link about BOV's:

Ok, anyway...back to the install.

The issue with T-7 and tapping the line to the BPV itself is that it will not read properly. There is a system that controls what the BPV sees, and you want to tap into the system that controls the BPV.

The line that goes from the throttle body to the solenoid that "controls" the BPV is the line you need to tap into to get a correct reading. This way your gauge sees boost *and* vacuum. Not just when the solenoid opens to pressurize the BPV.

Here is a picture:

Now that you have found the line to tap under the hood, GO SIT IN YOUR CAR.

Relax, have a beverage. Maybe try a few stretches too. You will need to be limber for the next part.

Now that you know where to tap the line, you need to pass it through the firewall. This is the fun part. There is a rubber grommet (yes, it's actually there) that you can pass the line through. It's above the gas/brake/clutch pedals and a pain to see.

You need to remove the kick plate that is by your shins when you are sitting in the drivers seat.

To do this, remove the 3 Torx screws on the underside, the 2 that hold the OBD II port in place, (push the port through the hole) remove the fuse Box cover, and remove the 2 torx screws that are in there. The last step is to remove the bolt and washer to the left.

Then yank. It should pop out.

For the next part, you basically have to lay on the driver seat with your feet on the roof of the car with your head under the dash. It's called "assuming the position" If you own a saab, you will assume this position several times. It's a fact.

Now that you are under there, look for the grommet. The grommet is oval shaped, and about the size of a golf ball. It's above the brake pedal.


It comes out behind the fusebox on the drivers side of the car. Some say you have to remove the fusebox to get to the hose you just shoved through the grommet.

I say NO, and here is why...

While your feet are on the headliner of your car, and your hands are all up in the dash, you will cut an 1/2" "X" in the grommet that passes through the firewall with a box cutter, or x-acto knife.

Before you start the install (because you read through this first) you need to find a ball point pen, and pull the insides out. Then cut a 1" section out of it (like a drinking straw).

Then you take the 1" section of Bic pen that you cut up, and stick it in the "X" you just cut.

Then, take the gauge line, and pass it though the bic pen from the interior side of the grommet.

The section of Bic pen allows the cheap, brittle, prone-to-creasing, plastic boost line that came with the cheap-ass ricer boost gauge you bought to pass through the grommet without binding up, and ALSO allows you to grab the end of the hose with a longish pair of needle nose pliers between the fuse box and firewall.

You can then pass the line to the proper solenoid, and then make the "t" that you need. Make sure you follow the gauge manufacturer's instructions when you hook it up. A leaky hose to the gauge can cause a boost/vac leak!

Now for wiring.

The best choice for wiring your gauge would be to tap into a dash switch back light. You want to do this so your gauge will dim along with the other lights on the dash.

You want to find the GREY and WHITE wire on the back of a switch, like this:

See the thing with the yellow dots on it?

That's called a TAP SPLICE and allows you to make a secure power tap into a wire without any cutting. You can also take it off easily when you eventually sell your car for a Subaru. You can find a pack of tap splices at most hardware stores, and Radio Shack.

The instructions that came with your gauge should give you all the info you need as far as power hookups and whatnot.

Here is a good spot for grounding, see the thin wire that comes in from the right side?

If you bought something secondhand, here are a few sites with wiring diagrams and install information:

Auto Meter:
Glow shift:
DEFI: (for the ballers)

· Registered
8,752 Posts
Palmer= teh bestest!

But theres no reason to put a boost gauge on my moms 9-5 linear, so perhaps on my dads Viggen, who knows?

· Registered
6,573 Posts
Pics from my boost gauge install on my NG900. Feel free to copy/use. You may want to point out the grommet etc:

Grommet, looking up from under the pedals

Grommet, poked out, screwdriver sticking through under fusebox

Vacuum hose coming out near A-pillar

Speedparts Gauge Pod installed

· Registered
6,573 Posts
Palmer, you pointed to teh wrong grommet.

The grommet is the one in the middle right, just to the right of the clutch pedal (you can see the clutch cable in the pic). The grommet does not have anything going through it. You poke it out and then you'll have the vacuum hose going through it.

· Registered
17,404 Posts
You can pretty much use any gromit - FYI, as long as you can push some vac hose through it and it doesn't pinch or obstrict the operation of other stuff under the dash or on the firewall then you're good to go!

· Registered
896 Posts
So, this write up is for T7's. For those of us with a T5, we can tap into the bov line which is direct from the intake mani? (I replaced this hose and IIRC it was direct. I have a autometer phantom on my desk and i miss it.
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