Here are some methods/tips that I uncovered as I did these installations in my own car. All installation described below preserve your existing OEM gauges and are applicable to just about any car. Anyone can easily accomplish these installation, just take your time!
A couple of initial notes... first, plan where you are going to place the gauge(s). A 3in diameter gauge in a 1in space is not going to work. There are a couple of ready made installation alternatives, such as A pillar pods for single and double gauges, there is a center vent gauge holder capable of holding 2 or 3 gauges (hint: if you use your A/C, use the two gauge with vent model). It would also be worth it to first get ahold of the gauge, just to check things out with gauge in hand..
The OEM shop manual is invaluable in this project, telling you how to remove panels, where to find electrical connections, etc. In fact, if you ever want to work on your car, the OEM manuals are better than any of the Chilton's genre and the price is not significantly more. Your owner's manual indicates how to order them with a phone and a credit card.
This installation talks about installing a Vacuum/Boost and an Oil Pressure gauge. You may find once you see how easy it is to do that you start installing lots of gauges!! The record for gauges in a T/E/L is held by the 4Banger - search the archives for the number, I am not ruining the surprise! Seriously, though, in order of priority you should should install 1) a Vacuum/Boost gauge, 2) Air/Fuel Ratio or Exhaust Gas Temperature, 3) Oil pressure gauge, 4) Voltmeter or Ammeter (specially those cars with serious sound systems), 5) Water or Oil Temperature (those who are racing may prefer this a no. 4), and so on... the sky and your dashboard is the limit!
Standard Disclaimer: Everything discussed here has been tried and has worked for me, but I am assuming that you have more than basic skills. If you are afraid that you will end up toasting your electronics, dumping your oil on the side of the road - get a trusted friend to help or better yet a good mechanic! Last, don't blame me when it breaks!! ;-)
You will need a gauge (of course!), with its associated tubing, hardware, and a plastic tee. Your gauge should, as a good minimum, be able to read from 30in of vacuum to 20psi of pressure - this range is quite common and easy to find in various sources from JC Whitney to our online vendors. Higher pressure range gauges are also available at a slight premium.
There are various places that can be monitored, but for expediency sake I will describe just one - the rest can be setup with a similar procedure. I personally choose to monitor the intake plenum, after the throttle butterfly, since this provides a monitor on the conditions of the air (pressure and/or vacuum) as it enters the cylinder - plus a monitor here will be the final judge on whether any changes made to the intake tract, before here, have made a difference or not on your power.
Our T/E/Ls have three convenient taps to this side of intake plenum, one goes to the air valve for recycling boosted air, one feeds the brake booster, and the last feeds the fuel pressure solenoid. It is this last one that we are interested in (the other two would also work but I prefer not to interfere in the least with my brakes or the boost valve). Find the line that leaves the intake and goes to the solenoid on the firewall. On my particular car, there was a plastic joint (which is either a calibrated orifice or an assembly easing widget) either way I used this opening to avoid cutting the lines (you can cut in at a different spot if you prefer) and added a plastic T.
I already had a convenient hole already available from a previous alarm installation, where the speedo cable crosses the firewall. Look around in the area, there are several places where there are grommets that can be used. If you cannot find one, you may have to drill one, but at least then you can place at your convenience, just use some touch up paint and some silicone to seal -- watch not to drill something that you do not want to!
Now comes the hardest part, mounting the gauge. Since this is an important function to monitor, which also changes rapidly, you will want to put this where it can be monitored without taking your eyes off the road. The pillar mount should fit that bill or you can mount in various places with commonly available aftermarket gauge pods. I have chosen the pillar pod. For the gauge lighting read on. That's it, you are now done except for tie wrapping the loose air tubing.
1. Can plastic tubing can be used instead of the copper line that came with my gauge?
Yes, most auto parts stores will sell the plastic line and the connectors/adapters. You can also find the brass hardware (adapter, T, connectors, etc.) at any good ACE hardware store - and its a lot cheaper than the car stores!
2. When you mentioned tapping the fuel pressure solenoid, you spoke of a calibrated sic - orifice or assembly easing - "widget". Would this be located on the driver's side of the car?, and if so, was there a rectangular plug covering the nipple?
Yes, I was referring to a black nylon male-male connector, kinda like a tube with nipples on either end, joining the vacuum line near the solenoid. Note that this is only for my car - it may not be installed in your car (different model year cars will differ in small details like this). Also note that there are two solenoids on my 1992 TSi, one of the solenoid does have a rectangular looking "plug" which is actually a vent to the atmosphere - do not tamper with this part! It is not the correct one to work with - read on.
3. When I look at my car, I see this plug covering the nipple with no hoses coming out that side of the solenoid. If I have found what you were speaking of, what do I then use the T fitting mentioned in your post? It would seem as though I could connect my gauge directly to this nipple.
Let me give you some better directions to assure your success.. Find an object on the driver's side of fuel rail (its on the end of the fuel rail) that looks like a tin can (it's the fuel rail pressure regulator) that has a vacuum line and a rubber fuel line connected to it. Trace the (thin) vacuum line back to the solenoid located on the driver's side of the firewall. Now, the line that feeds into that solenoid from the intake manifold is the one that you want to tap into (tap into the line anywhere it is convenient only make sure it is in between the solenoid and the intake manifold!).
It happened to be that on my car, on that line located near to the solenoid, there was a black nylon male-male connector installed which I replaced with my vacuum line T. I imagine that this connector was either to supply a calibrated orifice or to facilitate assembly of the car when the engine is installed - hence my reference in my original note (and yes, I believe it is just an assembly facilitating widget since everything is working fine..) One last thing, flexible nylon tubing should be tied down every six inches since over time they harden and will crack if they are flexing too much.
For those that are ordering & installing their new gauges, here's a few tips.
1) Order a 2 - 2 1/16 inch diameter gauge, if you intend to use an A pillar pod or the center vent holder - most pods/holders will not work with anything bigger.
2) Look for gauges with 1/8in plastic tubing instead of the 1/8 inch copper piping. If you did get one with copper pipe, just go to any well stocked automotive store and get the tubing kit.
3) Tie off and support the plastic tubing every six inches - it tends to harden as it ages and will fatigue if unsupported.
4) Most tubing hardware that you will need can be found inexpensively at any well stocked hardware store - that includes tees, ferrules, unions, etc.
5) When you install the gauge, shoot for a friction or press fit within the pod. That way the gauge will be removable without having to remove the pod. Also leave some slack in your installation to pull the gauge out to work on.
6) Any decent gauge will do, and will be 300% more informative than the dash gauge. JC Whitney, Jegs, Summit, Sun and the aftermarket suppliers mentioned on the web page all carry gauges that will work for you. Caveats: a gauge does not have to be expensive to be good, but you will get what you pay for.. - see point 5 for when you need to replace the gauge! JC Whitney has good gauges, but mostly in the 2 5/8 size. They only have two in the 2in size that meets all of the above. I got the "racing-style" mechanical boost gauge which is made by Equus and came with the different light condoms to match your lights. Note: if your gauge is acting erratically, first check your connections for tightness before assuming the gauge is bad - oh and keep the length of the line to the minimum needed.
7) A very convenient spot for connecting the gauge's light can be found behind the gauge cluster fascia of the pre-95 models. Remove the six screws and the fascia. Look for a unused connector installed behind the top left plug. It will have two wires, Green/White and Black/yellow, connect your light's wires to these and voila! Lights and dimmer control through the rheostat..
8) Throughout the installation you will be fishing wires through various small holes, a piece of coat hanger wire will make an excellent tool.
9) When trying to fish the wires into the A column, do it in two steps. Start at the hole where the A column fascia and the dash meet, in the door jamb. You should be able to run the fish wire directly down into the inside of the dash coming out near where the hood release handle was (you should remove the bottom cover for this exercise). Pull out plenty of length. Then pull the wires into the A column through the hole you cut for them. Pull them through the pod and install the pod with its adhesive tape. Those that wish can remove the A column fascia for an easier installation - the shop manual describes the steps to follow.
You will need the gauge (make sure it can read a minimum of 100psi - you would be amazed by how much pressure our engines put out at cold startup!) and its associated tubing, another tubing kit (yes, you will need this one since I choose a longer path for the tubing), a 1/8inch coupling to join the ends of the tubings, a 1/8inch female NPT pipe tee, a 1/8inch union (its a short male-male piece of pipe), a 1/8 inch - 27 NPT tap and die (to clean and shape couplings that do not fit right - you can also use a 1/8inch -28 BPT tap and die, in a pinch), some red Loctite, some high quality gasket making silicone and lots of paper towels. BTW, the best time to do this is when you are doing an oil change and have drained out all the old oil but have not yet filled the car up.
Needless to say, this gauge is a little more involved to install, so allow lots of time - we do not want any leaks. First, jack up the car and remove the front left wheel. Remove the inside cover and you will now be staring at the crank and the OEM electric pressure gauge.
This gauge can be removed with a wrench and set aside. Take your tee and assemble you male-male union to one side of the run (use Loctite here) but do not tighten all the way just firmly tighten for now - read on and you will see. Add the oil tubing coupling to the other side of the run also with Loctite. Clean and dry the old hole of the sending unit, apply some silicone to the end of the male-male union and thread your assembly (the tee, male-male union, and oil tubing coupling) into the hole. Now, as the assembly begins to tighten, the goal is to end up with the branch of the tee facing directly down so that we can install the OEM sending unit in it. Generally, one of the sides of the male-male union will give enough so that you can achieve this - if you are concerned about leakage, skip the silicone and use Loctite - but prepared for a bear if you want to remove this later.
As indicated, add the OEM sending unit to the tee's branch and connect its electrical connection. Check that the assembly will be clear from any moving or hot parts. Attach the oil tubing to its coupling (using care not to twist, kink, or damage it). (NOTE: I choose the following route since I did not like routing a line near my drive shaft - you may choose to do so, just make sure to tie everything with lots of tie wraps, allow slack for engine movement and make sure the line cannot touch any hot or moving thing!!! )
Now route the tubing so that it loops under the assembly, going towards the front of the car. Come up the near corner of engine well, attaching to the power steering cooler lines and route your tubing towards the firewall. Somewhere around here your tubing will not be long enough, so pick a convenient spot, cut off the remainder and attach the coupling to add on the new tubing line. (Don't forget to choose a spot where you can tie wrap firmly down the coupling!) Route your tubing through the firewall allowing lots of slack inside the car.
Now we must try to bleed out as much air out the line as we can. Get a container (like an empty oil bottle), and while holding the line inside the container start the car. As soon as oil comes out the line (watch for splash!), turn off the engine. Clean the end of the line, attach the gauge coupling and gauge. Go back and check for leaks, adding tie wraps where needed (keep line away for moving and hot things!!!!) It goes without saying that you should route the line inside the car towards your final position of the gauge.
Lights can be hooked up similarly like the boost gauge description above.
You should also have a small container in which to lay the gauge when you first try it out so as to check and catch any oil leaks (no nasty, hot oil inside our cars!).
Finally, double check everything for a few days to assure that no leaks have developed - a leak here can pump your engine dry in less than you think! (You may want to carry a quart or two of oil in your trunk for a while)
I repeat myself, take your time and do not route the tubing anywhere near any hot place, any moving or any sharp edges!!!