Nissan 300ZX Air Fuel Meter - Nissan 300ZX Injector Duty Cycle Meter

Nissan 300ZX Twin Turbo "In-Dash" Air Fuel & Fuel Injector Duty Cycle Meters

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. You will also want to know how much your Air Fuel Ratio is and how hard your Fuel Injectors are working.. For a start all the cash you spent on the ECU and other performance upgrades can be quantified if it lives up to the specs. Optionally, if you have gone the Electronic Boost Controller (EBC) route, you will want to see that your engine is not running dangerously lean. 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 "off the shelf" Air Fuel Meter And Fuel Injector Duty Cycle Meter from your favorite after market parts store, and install it somewhere in the car where it is guaranteed to look like an "afterthought" in some pod that sticks out like a sore thumb, and join the "Boy Racer" brigade. You could spend copious quantities of cash on an fully integrated computerized system if they are even available, 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 and Fuel Injector Duty Cycle Meter combination integrated into the Speedometer of the car's stock instrument cluster, to compliment our popular In-Dash Boost Gauge. It uses the car's stock 1v Oxygen (02) Sensor and the Number 1 Fuel Injector output to give real time Air Fuel Ratio and Fuel Injector Duty Cycle readings on 20 1.8mm LED Indicators. This article focuses on utilization of the car's stock sensor and injectors. Our Gauges integrate into the Dash (Check out this page for 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.

This article is for the real "Do It Yourselfer", 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)

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 also assume NO RESPONSIBILITIES what so ever for any accidents cause 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.

Main Control Units

As you can see by the layout, there are quite a few components. The signal comes into the unit from the Oxygen Sensor and the Number 1 Fuel Injector, we spliced into it directly at the ECU wiring of the car. Remember to DISCONNECT the BATTERY BEFORE beginning any electrical work on the vehicle. Now this is the Brilliant part. The whole thing integrates with NA cluster speedometer dial just beautifully.  We will cover the actual installation later in this article. This will of course make the NA cluster worth more, as, as of this writing they could be acquired  for about $75 - $80, where as the Turbo Cluster fetches well over $120.  It is as if it was made for the job.

Air fuel Meter & Fuel Injector Duty Cycle Meters Main Control Units, Not To Scale

The power for these devices is derived from +12 volts from the stock instrument cluster. It also needs a good ground. (Again the stock instrument cluster ground was used) Please refer to the following layout diagram for all the interconnection and external wiring information.

Air Fuel & Injector Duty Cycle Meter Main Control Units, Interconnection & Wiring Layout, Not To Scale

Installing The Gauges in the NA Speedometer Dial

This is the part we were quite concerned about doing, and a quick call to our friendly local junk yard and a poke around on eBay, confirmed that they were readily available at a very reasonable cost. So much so that we almost recommend that you buy one and modify it, leaving your stock cluster for some other work. 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 duty cycle monitor somewhere in your car. Or, get someone you trust that owns a nice quality drill press to help you out. It is so much fun to do any car buff would just be eager to help, especially on a Twin Turbo. If you do choose to remove the dash assembly for any reason, please do not forget to DISCONNECT THE BATTERY.

Step 1 - Remove The Dash Complete With Gauges and Wiring

This is a very easy procedure. We have a nice MS Word File that we scooped form www.300zx-twinturbo.com. You can refer to it for the complete procedure. It is based on the 1990 - 1992 model years of the car. Just click on the link below.

nissan300zxgauges\90-92clusterremoval.doc

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

Step 2 - Dismantle The Dash To Remove The Speedometer Dial

This is quite easy also, you just need to remove the 4 screws on the underside of the cluster, unclip the 2 metal supports held on by 2 of the screws you just removed. Then unclip the 5 plastic retaining clips.  The cluster cover and plastic screen come off in one unit.

Step 3 - Measure, Mark up The Speedometer 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 20 Boost Gauge LEDs in the NA speedometer dial. We made two quarter a of LEDs on the bottom of the speedometer dial. 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 other projects (Boost Gauge) we are installing in the Speedometer dial, which is described in another article. You will notice that we are first using a piece of sheet aluminum ($5 from your favorite hobby shop) to make a rigid template that we can then drill the actual dash with. This is a good idea as if you mess it up you have only spent $5 + your time. We then put it over the tachometer dial for the actual drilling process. Creating the template can be done a number of ways, this step describes how we went about doing it. You will need a ).070" high speed steel drill bit for the indicator holes.

Combination Speedo & Tach 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 the template's outer edge as close as possible, Cut out the 3/8" inner circle (Fine Blade Hobby Knife) and we were done.

Speedometer Drilling Template

• 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, mark one top and one bottom with arrows to the top so you can line then up.
• 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.
• Then remove the template, and using a 3/8" drill, carefully drill the center hole very slowly, we used a small drill to pilot the hole first then finished the hole off with the 3/8".
• Cut the 3/8" center hole out of another paper template with a razor knife and put the 3/8" drill through it and the TOP alloy square. Align it so it looks square then stick it down. We used DRYLINE YELLOW glue strip by liquid paper.
• Then we used a 5/32" drill and a 5/64" drill to line up the holes in the dial with the ones in the template. Then we double checked everything. We used a 3/8" diameter socket in the center hole to align them exactly.  To make sure the template is secured to the dial face, we used Liquid Paper Dry Line removable paper adhesive for extra hold.
• Drill the 6 dial alignment holes, countersink the bottom, and find 6 countersunk screws and nuts, remember these are for location purposes and should not foul on the dial edges.
• De-bur everything.
• Cut the 3/8" center hole and the 6 alignment holes out of yet another paper template with a razor knife and put the 3/8" drill through it and the TOP alloy square. Align it so all the alignment holes in the aluminum template line up perfectly with the paper template and stick it down using double sided tape or DRYL.INE YELLOW glue strip by liquid paper.
• Now center punch all the other 20 indicator holes.
• 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.

Step 4 - Drilling The Tachometer Dial!

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 3000 rpm.

• Place the dial in between the aluminum template, use the shanks of 3/8", 5/32" and a 5/64" drill bits to line up the center, top and bottom holes respectively.  Now put the scews and nuts in the alignment holes and 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 3000rpm, 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.

Speedometer Dial Drilled Ready for LED Mounting, & the Baby of a Template that did the Job

The above photo shows all 20 1.8mm LED holes, in two quarter circles for the Gauges.  As you can see it is a very tight fit. But we were really pleased with the out come.  Now onto installing the LEDs and the electronics.

Step 5 - Installing the LEDs

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.

   Speedometer Dial, Drilled with Lettering Applied

Here is how we installed the LEDs.

• Make sure you 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 you 20 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.
• 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 24 hours to dry. you can cut off excess caulk with a small razor blade or a hobby knife.
• 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 LEDs Installed for Integrated Boost Gauge

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 1/4" 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 straight line as close to the caulk surface as you can get. Ours were about 1/4" from the rear face of the dial to the top of the leads when bent.

Speedometer Dial, with LED Anodes Wired Together

• Bend all the cathodes at right to each other, the last one will stick out a little. Once bent there should be only about 1/8" of lead after the bend. Line them all up so there is no contact between them.
• Then we wired each of the leads to each LED one by one. Make sure they originate from the right of the dial as you are looking at it from the rear. All LEDs were wired in backs of 10 so the wires for each bank emerged from between the 4500 and 5000 RPM markers for 1 - 10 and between 5000 and 55000 RPM markers for 11 - 20.
• There are actually 21 wires as one is for the common anode wire. Make sure you remember which is LED 1 - 10,  we test each one with a 5v supply and a 2.2k resistor before soldering them into the boost control board.
• You may want to shape the wires into a loom and tie them off with a very small tie wrap, you will find that most 28 swg wires will roll up to about a 1/4" in diameter.  This is tricky and should be done so that the wires do not foul on any parts of the instrument cluster.

Tachometer Dial, with LEDs Installed and Wired for Integrated Boost Gauge

• Getting the Dial back in the cluster is quite easy. We added some double sided tape onto the middle of the dial so it would stick to the plastic light pipe.

Step 7 - Rebuilding the Instrument Cluster

Depending on what wires you used for the LEDs you will need to cut two small holes in the White Plastic Tachometer backing. Simply re-assemble the cluster in the reverse order that you took it apart. We ended up cutting 2 slots as can be seen in the photo.

Cluster Assembly, Showing Cuts for Wire Routing

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 and a Normally Aspirated Speedo Dial

Step 8 - Testing & Wiring Up The Gauge Circuit Boards

This part is pretty straight forward, if you are electrically inclined that is. The LEDs were wired to the Printed Circuit Boards (PCBs) using the wires that we wired in Step 6. It is best to keep the wires as SHORT as possible to reduce any interference or noise, although we never experienced any problems and the circuit is compensated for longer LED leads. 12" should do the trick. This ends up being 5" outside the cluster, this is more than enough so the control box can be tucked away below and to the left of the cluster once installed in the car. It is a good idea to check each LED before you finally solder them to the PCB. If you use a 3k Ohm resistor with a 12v power supply or a 9v battery will also work), you can easily check each wire and establish which LED it represents, then wire it to the appropriate pin on the PCB. Simply connect the +12v lead (or the +9v from the battery) to the common anode wire you marked earlier, then connect the -ve lead to the resistor and touch each LED wire with the other end of the resistor. The appropriate LED will light up dimly in the cluster to let you know all is OK. If you get problems with multiple indicators lighting or an indicator does not light, now is a good time to diagnose and fix it.

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

This part is pretty straight forward, if you are electrically inclined that is. The LEDs were wired to the Printed Circuit Boards (PCBs) using the 28 swg wire that we wired in Step 6. It is best to keep the wires as SHORT as possible to reduce any interference or noise, although we never experienced any problems and the circuit is compensated for longer LED leads. 9" - 12" MAX should so the trick. Referring to the Circuit Layout, wire the 10 LED Indicator wires from each gauge and the +12v common anode LED power to their respective Control Units. Make sure you get the correct bank of indicators to the correct control unit. Then the PCBs were placed in an enclosure and tucked behind the cluster. There are four other wires that need to be connected to the car in order for the gauges to function correctly. The + 12v in from the battery (Red Wire).  Make sure this is wired so it comes on only when the ignition is on. Ground (Black Wire), this can go to any solid car ground. Try to use a common ground used by other devices on the car so you know it is good. Then the two signal wires need to be wired to the car's ECU. The Injector Duty Cycle Wire (Green Wire) goes to the Number 1 injector driver pulse.  This can be taken from the ECU Pin 101, it should be a WHITE Wire.  The Air Fuel Meter can go to any of the car's Oxygen Sensors. These are Pins 55 or 29, also WHITE wires.

To test the setup before wiring up the sensor wires perform the following:

• Turn on the car's Ignition so power is connected to the gauges.
• The Number 10 Indicator for the air Fuel Meter will be the only Indicator illuminated.   
• Ground the Air Fuel Meter Signal wire momentarily, then remove it and let it float. All the indicators will go off, then each one will illuminate and then go off until Number 10 is left on.
• Ground the Injector Signal Wire. All the Duty Cycle Gauge Indicators will illuminate until the ground is removed from the signal wire.

Step 9 - Setup & Calibration

There is no calibration required for the Air Fuel Meter and The Injector Duty Cycle Meters.

Step 10 - Admiring the Finished Product

The following photos show various close ups of the dash after re-installation into the car.

Complete Dash Mounted in the Car

We hope you find this article interesting. If you would like more information please Email us or go to our Gauges For Sale pages.

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