VW Passat  "In-Dash" Air Fuel Ratio Meter

Before and especially after additional performance modifications have been completed and installed, it is imperative we know whether the Electronic Control Unit/Module (ECM/ECU) is providing the engine with enough fuel under high boost and/or load. First you will want to know how much boost your turbo chargers are providing you with. Second you will want to know whether the Injectors, ECU, Fuel Pump Etc. can provide the correct amount of fuel for the added boost. For a start all the cash you spent on the ECU can be quantified if it lives up to the boost and mixture specs. Optionally, if you have gone the electronic boost controller route, you will want to see the stock ECU is capable of controlling the fuel deliver process correctly. Air Fuel Ratio at eye level becomes a very handy addition to the car's stock gauges. Air Fuel Ratio must be monitored closely when doing turbo upgrades and other inlet manifold pressure related performance modifications. Now, you can go and buy an cheap and nasty "off the shelf" Air Fuel Meter from your favorite after market parts store, and install it somewhere in the car where it is guaranteed to look like an "afterthought" and join the "Boy Racer" brigade. You could spend copious quantities of cash on an integrated system, or you can do a proper job, with the satisfaction that you did it all yourself.  And hey, that is half the fun, isn't it?.  We chose to build and design our own Integrated Air Fuel Meter integrated into the Tachometer of the car's stock instrument cluster. It uses the car's stock 1 Volt Oxygen Sensor readings to give real time Air Fuel Ratios on 10 1.8mm LED Indicators. Indicator number 1 is Lean and 10 will be Rich. Our Air Fuel Ratio Gauge integrates into the Dash (Check out this page for a kit of component parts or a complete unit) so it looked as if it was there from the factory. This takes a lot of planning and measuring, in the long run it will look perfectly acceptable to the most discriminating connoisseur.

Disclaimer (Please Read it Thoroughly)

By connecting and using this Custom Gauge you agree that the designer and author of this document and gauge is in no way responsible for damage to persons, a vehicle or vehicles as a result of installing meter.

Liabilities: The author and designer assume no responsibility for the modifications you do on your car. Although to our knowledge these instructions are accurate, this includes any errors that these instructions may contain, any differences between your car and the one(s) showcased, as well as any errors in following the instructions. If you don't feel comfortable working with automotive electrical wiring we suggest you let someone with some experience do these modifications. The installer should posses a good understanding of the electrical system of the vehicle being worked on.  Please double check all your connections and ALWAYS work with the car battery DISCONNECTED.  Always keep your safety and that of others as the highest priority.

Warranties: The modifications described in this document could potentially void any manufacturer's warranty you may have left on the car (not likely, but possible nonetheless). You assume all responsibility if your car is still covered by warranty.

Legalities: Laws in your country/state/region/whatever may not allow you to modify systems such as these on your car, the penalty being at least a fine. Please check with your local authorities to be on the safe side.

We assume NO RESPONSIBILITIES [emphasis added] what so ever for any accidents caused by the driver gazing at this tremendous addition to the stock instrument cluster while they should be concentrating on the road and their driving. We always endorse good and safe driving practices at all times.

With that, good luck, and have fun with this Custom Made Gauge.

Please note, that if you have any problems with the ECU or the ignition timing on your car you will get inaccurate readings from this meter.

With that, good luck, and have fun with this Custom Made Meter.

The first thing you need to do is acquire an electronic Air Fuel Ratio Meter as described in this article (And on this page).  You will need to be reasonably proficient with a soldering iron and lead solder, as you will be using them a lot. (Or you could get someone else to do it)

This article is for the real "Do It Yourselfer", we designed and built our own Custom In-Dash Air Fuel Meter, and that is what this article covers.

Completed Unit

Main Air Fuel Meter Control Unit

As you can see by the layout, there are quite a few components. The signal comes into the unit from the car's O2 sensor, we spliced directly into it directly at the ECU of the car. Remember to DISCONNECT the BATTERY BEFORE beginning any electrical work on the vehicle. This signal wire is different on different years of the car so please consult you repair manual for the exact location.  You can also trace the wires from your front or rear O2 sensors and tap them directly at the interface plugs inside the engine compartment. We also tie wrapped the signal wire to the main wiring loom on route to the firewall access hole. Sometimes this signal can be very sensitive, and subject to noise.  It may require a shielded ground to be routed along with it. Ours worked fine without any shielding. Once spliced in, the wire can be run through the existing hole(s) in the firewall. We used Pin 1 or Pin 2, one of the two thick BROWN Wires of the large plug for our ground,  and Pin 3 the thick BLUE/BLACK wire for switched +12v.

Main Control Unit, Not To Scale

Please refer to the following layout diagram for all the interconnection and external wiring information.

Main Control Unit, Interconnection & Wiring Layout, Not To Scale

Installing The Gauge in the Dash

This is the part we were quite concerned about doing, and a quick call to our friendly dealer and spotting some eBay Auctions, confirmed that to replace the dash was a relatively inexpensive option, reassuring us that the parts we were about to potentially destroy were available as replacement parts. Armed with this "insurance" we proceeded very cautiously. The following steps involve drilling and cutting the dash assembly. Unless you are pretty good mechanically, we recommend you simply read this for interests sake, and put a commercially available boost gauge somewhere in your car. If you do choose to remove the dash assembly for any reason, do not forget to DISCONNECT THE BATTERY.

Step 1 - Remove The Dash Complete With Gauges and Wiring

This is a very easy procedure. You can refer to the car's repair manual for details. We proceeded as follows:

• First remove the fuse box cover on the left of the car's cockpit. It simply pulls off. Put it to one side and store.
• Remove the 4 bolts holding the color coordinated drivers side knee panel and slide this forward and rest it on the drivers side carpet.
• Remove the 2 screws on either side of the thin plastic trim that goes all the way round the steering column. It has a plastic insert in it that moves as you raise and lower the steering column.
• Remove the 2 small screws holding the upper steering column cover and remove it completely. The lower cover need not be removed.
• Put the cars steering column tilt in the lowest position and lock it.
• Gently raise the plastic insert on the top of thin plastic trim that goes all the way round the steering column.  Using a long necked torx screwdriver remove the remaining screws holding the plastic trim ring in place. This is quite tricky be sure to find the screws if you drop them.
• This will expose the 2 torx screws that hold the Cluster in place. Remove the 2 Torx screws.
• Gently pull the cluster forward so you can get at the 2 plugs on the back, there are little clips holding them in but they are easy to do if you have a little bit of finger nail left. (After all the chewing you did contemplating this modification)
• Remove the dash assembly by pulling it forward and tilting it down to the left. Place it on a clean protected workbench. (We used towels to protect the dash form unnecessary scratches)

Now that you have removed the dash assembly, the fun can begin.

Step 2 - Dismantle The Dash To Remove The Tach Dial

This is quite easy, you just need a few nifty little pieces of plastic or metal. We used 1/16" plastic sheet.  We use a lot of this plastic sheet, where do we get it? you may ask.  Well, you know those three ring binders you use all the time for files, at the front and rear there is usually a sheet of plastic, either white or black used to support the pages.  That is what we use.

• Cut six pieces of 1/16" plastic about 3/8" x 1"
• Place the dash assembly face down on piece of cloth.
• Remove the two Torx Number 10 screws from the rear edges of the unit.
• Using a small screw driver, slowly  lift the six the plastic retaining clips and slide a single cut piece of plastic under each one.
• Very carefully and pop the cover off. Store it in a clean safe place.
• Mark where the tachometer needle is pointing when fully anticlockwise against it's internal stop. You will need this for when you put it back.
• Now gently, turn the needle anti-clockwise while pulling up on it. It will pop off as it is only a push fit.
• Now the Tachometer dial can be removed by turning it anti-clockwise and lifting it off the keyway.
• Get ready for the scary part coming up next.

Step 3 - Measure, Mark up The Tach Dial and Prepare for Drilling LED Mounting Holes

This is the very tricky bit. It can be done a number of ways, this step describes how we went about doing it. We chose to locate our 10 indicators (1.8mm ) in the Tach dial. We made a straight line indicators between the stock Tachometer numbers and below the indicator lamps. The measurement was not that easy.  A template was created after many, many iterations and here is what it looks like. It includes the layout from another project (The Integrated Boost Gauge) we were installing, which is described in another article. You will need a ).070" high speed steel drill bit.

Tachometer 180 Degree Dial Drilling Template

Here is what we did:

• Print the template to scale on thick bond paper. (Best quality) Only print 1 per page to keep the scale.
• Cut 2 4 1/2" squares of about 1/10" Aluminum sheet or there abouts, you do not want any thicker, it is too hard to work with. These pieces should be about 1/4" larger than the dial all round. They do not need to be perfectly square.
• Clamp them together, mar one top and one bottom with arrows to the top so you can line then up.
• Drill the 4 corner holes, countersink the bottom, and find 4 countersunk screws and nuts, remember these are for location purposes and should not foul on the dial edges.
• Temporarily stick a template to the top and mark only the center hole as close to the actual center as you can without having any of the dial locating holes off the edge of the alloy square.
• Carefully drill the center 1/2" hole very slowly, I use a small drill to pilot the hole first then put the 1/2" drill in.
• De-bur everything.
• Cut the 1/2" center hole out of another paper template with a razor knife and put the 1/2" drill through it and the TOP alloy square. Align it so it looks square then stick it down. I stick it using the DRYLINE YELLOW glue strip by liquid paper.
• Now center punch all the other holes and do not forget the alignment hole at the very top, ever so slightly to the right of 12:00 O'clock on the template, as well as the one at 9:00 O'clock.
• You will punch 22 holes all together.
• Using a very slow drill and your newly acquired 0.070" drill drill them out and de-bur them.
• Clamp the bottom to the top, and now using the top piece as a guide you can drill the bottom.
• Voila! One sandwich style aluminum template.

Dash Drilling Template, With Key Detail, Top & Bottom (Note Location Hole at 12:02 Position)

   Step 4 - Drilling the Tachometer Dial and Applying the Lettering

As we only had one chance to get this right, we checked and double checked our measurements, and then we checked them again. The drill we chose was a 0.070". of an inch. (a tick smaller than needed for 1.8mm LEDs), We used a drill press at 2340 rpm.

• Place the dial in between the aluminum template, use the shanks of 1/2", 1/4" and a 0.070" drill bits to line up the center, left and top alignment holes respectively.  Now tighten the 4 nuts on the countersunk screws to hold the dial in place securely.
• Using the 0.070" drill and a speed of over 1750rpm, carefully and SLOWLY drill out the holes.
• Remove the template screws and take out the dial being very careful not to scratch the face. You should have something that looks pretty good.
• Stand back, admire your work, and congratulate yourself on the fine drilling job you just did...... You deserve it. In fact, go get a beer.

Now you will want to apply the Dry transfer lettering to your newly drilled tachometer in order to get that professional look and feel. This is not too hard to do providing you take your time and do the job properly. Make sure your hands are clean and free from grease and dirt.

Here are the steps we took to do our example:

• First take the dial and stick it to a sheet of clean paper with painters masking tape. Use the not too tacky kind (the cheap stuff) so as not to leave an adhesive residue on the dial.  Test it first in an inconspicuous area of the dial.
• Select the area where you want to place the lettering and use a strip of masking tape to get a straight line to use as a guide.

Tachometer Dial Drilled Ready for the Lettering

• Carefully align your lettering on the masking tape straight edge and gently apply the lettering using a ball point pen or a special dry transfer lettering burnishing tool.

Tachometer Dial with Lettering

• Repeat the above process for all the lettering you have to apply, being very careful not to mask the lettering. Otherwise it WILL come off.

Tachometer Dial Masked, with the Numerals

As you will see in the photos that follow later in this article, it was a tight squeeze.  

The above photo shows all 10 1.8mm indicator holes in a straight line.  It is also VERY difficult to ensure the holes are in exactly a straight line. Make sure your template is good before drilling you dial. As you can see it is a very tight fit. But we were really pleased with the out come.  Now onto installing the indicators and the electronics.

Step 5 - Installing the Indicators

This is the most time consuming of all the steps.  It is not hard to do, just slow. As you can see in the above photo of the dial, we applied 12 point white dry transfers to the dial. You can choose your own numbers and letters, just be careful not to obscure the warning decals on the dial.  The decals are clearly visible when you hold it up to the light.

You will need the following items:

• A tube of colored adhesive household caulk, we used a non silicone based white tub and tile type that you can get from your local hardware store. You want a color as opposed to a clear so that when the dash backlights are on, you do not get light through the LEDs from the back when they are off. Any color will do.  Black would block the light, so it is a good choice also.
• A clean lint free cloth.
• Three small (approximately 1" x  1/4") pieces of 1/16" thick plastic or wood. We used 1/16" plastic sheet.  But you can use thin modeler's type ply wood, just make sure they are clean and have no sharp edges.
• Some white lettering 12 point Dry Transfers, these can be pickup up from a local hobby shop.
• A lot of patience.

   Here is how we installed the LEDs.

• Make sure your hands are clean and dry. And when handling the face of the dial us a clean cloth or lint free tissue paper.
• Place the dial face down on a soft flat surface, a towel or piece of felt is good Make sure the LED holes are not obscured.
• Line your 10 LEDs in the color order you wish to have them, so they are close at hand.
• Offer each one up to their respective position and pop them into the dial from the rear, they should be an interference fit. each one should hold in place quite nicely. Do one at a time, remembering which LED goes in which hole. Sometimes the different color LEDs vary very slightly in diameter.

Tachometer Dial, with LEDs Installed, Showing Optional Boost Gauge

• Now, one at at time position each LED and apply a small bead of the caulking round it. (We used a small toothpick to spread the caulk evenly) Make sure you get all the cathodes and anodes (the anode is normally a little longer than the cathode) on the same side because you will have to join them together later. We found that setting 3 or 4 at a time then letting the caulk dry was the best way to go. Once they are all set, leave for 12 - 24 hours to dry. You can cut off excess caulk with a small razor blade or a hobby knife.

Tachometer Dial, all Caulked & Ready to Wire Up

• We painted the caulking black once it had dried, just to be 100% sure that no light got through.
• Stand back, drink another beer and admire you results again. Now doesn't that look sharp?

Tachometer Dial, with Indicators Installed

Step 6 - Wiring Up The LEDs

You can do this any way you wish. We used 28 swg stranded wire with a very thin insulation.  You need as thin wire as you can get.  28swg is the thinnest we wanted to go and stranded wire is more flexible than solid, although there is no real reason that solid wire could not be used. We wired 20 LEDs one by one , starting with the closest to the exit point.

• Cut all the Anode Leads (they are usually longer than the Cathode) on the LEDs to about 1/2" in length.
• Bend them at right angles to each other, overlapping them slightly, so you can solder them together. The last one will have to be bent in reverse of all the others so as to be soldered to them.
• Solder them all together so they are in a nice circle as close to the back of the LED as you can get. Ours ended up about 1/4" from the rear face of the dial to the top of the leads when bent and soldered.

Tachometer Dial Rear, Indicators Ready for Wiring - Indicator Anodes all Wired Together

• Cut all the cathodes to about 1/10" above the LED back.
• Then we wired each of the leads to each LED one by one. Make sure they originate from the left of the dial as you are looking at it from the rear. We made each wire 9" from the exit point which in this case was the 10th LED. So all the wires ended up on the left hand side of the tack dial when facing DOWN. This will actually come out of the right hand side of the cluster when assembled.
• There are actually 11 wires as one is for the common anode wire. Make sure you remember which is LED 1 - 10. You can either mark the wire with masking tape or as we do simply test them with a 5v supply and a 2.2k resistor. This will also prove they are all working. It is easy to damage LEDS with too much hear when soldering.
• You may want to shape the wires into a loom and tie them off with a very small tie wrap or tie wire. We in fact simply used 12 pound test fishing line every inch or so. This is quite tricky and should be done so that the wires do not foul on any parts of the instrument cluster.
• Bend the loom down so it runs parallel to the Clock Cut Out about 3/8"towards the edge of the tachometer dial left side when facing down. Refer to the pictures below for some helpful hints.
  
  An alternate method of wiring is also shown, on some installations we chose to split the loom. 11 are on the right side (looking at the rear of the dial) and 10 on the left. Make sure the wire lengths are the same for both looms. In this case they will both have the same exit point from the cluster so the loom on the left actually has slightly longer wires.

Tachometer Dial Rear, Showing Indicator Wiring

• Getting the Dial back in the cluster is also quite tricky. You cannot rotate it as the LEDs are in the way. What we did is place it down flat, and gently pressed it onto the keyway, being very careful not to damage our lettering.  Actually we pressed a little too hard on the letters and had to redo a couple of them. You will find it will eventually clip down into place. This is the only really tricky part of the installation.

Step 7 - Rebuilding the Instrument Cluster

Depending on what wires you used for the LEDs you may need to cut some plastic out of the White tachometer housing backing. We ended up not needing to cut anything.  The black instrument cover will however need to be cut so the wires can get through.

Tachometer Cluster Assembly, Showing Cuts for Wire Routing

This is what we did:

• Located the wires evenly down the right hand side of the Clock Assembly under the tachometer dial. (Looking down at the cluster.)
• We then offered the cover onto the cluster and marked where we wanted to have the wires come out. they come out of the cluster, turn a sharp left and then come out of the black cover.  It happened to be located right on a molding mark on the plastic. You can just see the molding in the photos below.
• A hole/slot was then cut out of the cover at the marked location. It turned out to be about 1/4"" in diameter open at the bottom (see picture below) It was easily cut out with a small  hack saw, then shaped with a file. Be careful not to get any plastic filings in the clear plastic face.
• The cables, now rolled up at this point were routed around the clock assembly and through the hole/slot. This worked out fine for us.

Tachometer Before Installation, and AFM Control Board Location on the Rear of The Cluster

Here is a nice photo of the finished tachometer mounted in the cluster ready to go. If you click on the photo you will see it in action.

Tachometer Installed in the Cluster and Powered up

We hope you find this article interesting. If you would like more information on this great mod, please email us or go to our Gauges For Sale pages.

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