Hi all,
Just a quick DIY write-up on installing a boost gauge in your P2 (I did this install on my S80 T6, the gist of it will work for all P2s, particularly the hose routing, but some steps will differ and as usual YMMV for exact the install process). One thing of key importance too is that this specific process will only work for 1999, 2000, 2001 and some very very early 2002 S80 T6 models. 2002-onwards models switched to the B6294T and also removed the recirculation valve from the intake system, and all 5cyl cars have the CBV on the compressor, so you will have to tap into another vacuum line from the manifold.
Supplies
For this install, you're going to need:
- A boost gauge (duh). I used a Turbosmart -30-0-30psi 52mm mechanical unit, although any boost gauge will work. I would recommend one that can read to at least 25psi, as being able to see when your boost spikes (T6s spike pretty badly if you punch it while in 1st, sometimes over 20psi because of ME7's slow boost control logic)
- Enough vacuum tubing to reach your chosen boost/vacuum source from the dash (if you're using a mechanical gauge). The gauge I bought did not have enough so I had to grab some 4mm vacuum tubing from my local auto store.
- An inline filter. Any filter will work, I recommend them as it stops any oil/particulate matter from reaching your gauge, or if you have an electronic gauge, they're pretty much mandatory to avoid damaging the sensor with oil. It also helps to absorb pulses from the intake system when using a mech gauge, which will give a steadier, smoother reading.
- A fuse tap and a ring terminal. You can tap into some other part of the wiring loom instead of using my solution, I chose the fuse tap and ring terminal solution because it means I can easily reverse the install later if I want to.
- A suitable T piece to tap into your vacuum source. I used the one included with the gauge as it fit the recirc's boost/vacuum reference line perfectly, but if you're tapping into another vacuum source (such as the fat line off the side of the manifold) you'll need a different sized T piece.
- Some way of mounting your boost gauge. I used a Turbosmart mounting cup as well, although it required drilling to install it so if you're not into that, I would recommend getting a gauge stand/cup that has an adhesive mount.
- Approx 2hrs of your time, beer and/or friends to "help" are optional but recommended.
Step 1: Choosing where to mount your gauge.
This step is pretty important as it decides where your gauge will sit and how exactly you will run the boost tubing and wiring. I mounted mine to the A pillar (see below). If you're using a cup or stand, dry assemble your gauge and gauge cup and play around with it until it's sitting exactly where you want it to. Make some sort of reference/witness marking so you can set it back up there later. If you're drilling to the A-pillar, I suggest using tape to hold the foot of the cup in place so you can remove the trim to drill into it safely.
Step 2. Wiring the boost gauge lighting (optional for mech gauges)
To wire in the boost gauge's lighting, I simply used a fuse tap and an 8mm ring terminal. The positive line was crimped to the fuse tap wire, and an additional fuse installed. The tap assembly was installed into the fuse for the cigarette lighter, and that fuse was also inserted into the location provided on the tap. I then removed the upper 10mm bolt in the fuse box next to the door seal, inserted it through the ring terminal (with the negative wire already crimped on) and rebolted it to the chassis. This is a solid ground to the chassis and I have had no grounding issues.
Run the two wires up through the small gap between the dash and door jamb, then push them between the A pillar trim and dash, see below for an example.
Step 3. Running the reference tubing (or sensor wiring).
Thankfully there is a fairly simple method of getting the tubing into the engine bay without disassembling half your dashboard (If you're using an electronic boost gauge with a remote sensor, these instructions will work as well, just install the sensor where it won't be subjected to intense heat (aka, not six inches from the intake piping or intake manifold), connect the tubing from the sensor the same way, and run the wiring the same way as the instructions below. First things first, open your bonnet, reach down to the left hand/driver's side of the intake manifold, and you should see a large, black, somewhat-cylindrical item with a black vacuum line running into the top of it. This is your recirculation valve (sometimes called a blow-off valve or diverter valve). For future reference, this is a standard Bosch valve. There are two methods of tapping into this line. The first (which I prefer and will go into detail below) involves adding more tubing and the T-piece between the valve and the existing tubing. The second method is simply to cut the tube that's already there and connect the T-piece in the middle. The first method is as follows;
First, use a pair of needlenose pliers to squeeze the 3 tabs on the clamp that's on the DV's top nipple. Slide the clamp up the hose past the nipple, then release the clamp. Pull straight up on the hose to disconnect it from the DV. Take your T piece as well as a short piece of vacuum tubing. Connect it to the straight section of the T piece and then slide the clamp from the existing line onto this tube. Slide the existing vacuum tube onto the other end, and then connect the tube that will go to the boost gauge to the T section. Slide the new tube over the nipple on the DV, and then squeeze the clamp tabs again and slide them past the barb on the nipple, then release. Once all this is done, your DV will look something like this:
Once you've done that, start running the tubing towards your boost gauge. I ran mine over the airbox intake pipe (and put a ziptie around it just tight enough so the hose isn't flopping around, but not so tight as to squash the tubing), then alongside the front end wiring harness going across the radiator, ziptying the lot together as I went along. I put the inline filter at where I had measured the included tubing would end up (just near the right hand headlight, see below), although adding a bit of slack to take into account my guesstimation. You can install the inline filter wherever it will fit, it doesn't matter too much, although keep it in the engine bay for simplicity's sake.
The pipe then runs past the ECU/TCU box, and the power steering reservoir.
It then runs up onto the lip of the chassis (be careful where you position the tubing here, else it will get squashed by the bonnet when it closes.) and into the gap between the guard and chassis.
Open your driver's side door and feed as much of the tubing through as you can, then walk around to the other side of your door, and pull the tubing through. This next part is probably the trickiest part of the install and is what will probably consume the most amount of time (and cause the most consumption of beer). Once you have fed the tubing through the guard and you have it hanging loose in the door jamb, put your hand in between the door and chassis, just above the height door arm and below the upper door hinge there is a firm rubber, disc-shaped object. Grasp it as best as you can, and pull it out of the chassis. This will take a bit of effort and you won't tear it, so you can pull with a modicum of force. Once you have this out, find a drill bit roughly the same size as the OD of your tubing, and drill a hole through the center of this rubber piece. Feed all of the loose tubing through it. If you put it back on before, remove the fuse box cover. Approximately 2/3rds of the way down it, next to the weatherstripping, should be a foam plug. Pull this out as best you can without tearing it. You're then going to want to feed the tubing through the gap filled in the chassis by the grommet, and then through the hole the foam plug previously occupied. This will take more than a few attempts, and a second pair of hands to shine a torch through the large hole so you can see is invaluable. Once you have fed it through, pull some more through, then take the large rubber grommet in the door jamb and slide it down the tubing so you can put it back into the hole it previously filled. It's important you put this back, else you'll end up with air/dust/water/other crapola rushing into the massive hole. Pull the rest of the slack through the grommet and hole in the fuse box, then put the foam plug back in the smaller hole where it came from.
Once you've done that, pull the weatherstripping off the door frame a little bit, and run the tubing up between the chassis and black plastic dash/fusebox frame, then across and tuck it between the dash and A pillar, just like the gauge wiring. Push the door seal back on, this will also help hold the tubing in place. Mount your gauge how you want it again (if you haven't already), and measure how much tubing you will need to reach the nipple on the back of the gauge. Cut off the excess, run the tubing into the gauge cup (if you're using one), connect it to the back of the gauge, then reassemble the gauge and cup, and reinstall the fusebox panel.
Congrats, you're done! First things first, insert your key and turn it to the accessory position (I). Your gauge should light up (if you connected the wiring), or if you have an electronic gauge, it should go through its startup/self-calibration sequence and then set the needle to 0psi. If it doesn't, check all of your wiring connections. If it works, start your car, the gauge should start reading a decent amount of vacuum. If it doesn't, check that you haven't accidentally nicked the tube or disconnected it somewhere. Go for a test drive, check you're making ~10psi of boost on the gauge (S80 T6s only, other models refer to the service manual or other sources for correct pressure). If you're not, and the car feels more sluggish than before, you probably have a split or leak somewhere along the line, causing the diverter to be forced open because there's not enough pressure to hold the diaphragm in the DV shut. If you're getting correct readings, congrats, you've installed it correctly. Enjoy your gauge, and the decrease in fuel consumption from hitting boost to watch it move :P. I'll get a video up of the gauge working soon.
