Lotus Esprit V8 "In-Dash" Air Fuel Meter Cycle Meter

Now that 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. If the mixture is to weak, and the engine is starved at high boost and/or load levels, irreversible (and very expensive) engine damage can occur.  In order to ensure this does not even get close to happening, Air Fuel Ratios must be monitored closely during any high performance testing situation.

Now, you can go and buy a meter from your favorite after market parts store, and install it somewhere in the car where it is guaranteed to look like an "afterthought", or you can do a proper job.  We chose to build our own Air Fuel Meter (AFM) and integrate it into the Dash so it looked 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.

The first thing you need to do is acquire an electronic AFM unit, or make one using our kit as described in this article.  If you purchase one, you will need to take it apart and remove the LED indicators from the module and install them in your dash. 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 Air Fuel Meter, and that is what this article covers.  If you buy one ready built, and want to install it in your dash, as we have, then simply skip the layouts sections and go directly to the in-dash installation.

Main PCB Layouts

As you can see, there are a few components. The signal comes into the unit from the driver's Oxygen (O2) Sensor.  Our unit is designed so that when you tap the car's stock O2 sensor wire there is absolutely no drain on the sensor. So there is not need to worry about "Check Engine" lights coming. If you installed the Boost Controller mentioned in a previous article, you already have the wire in the cabin. If not, this is how we did ours. We unwrapped the ECU wiring loom about 2 inches, located the O2 sensor signal pin, spliced into it, and re-wrapped the loom.  This task took a grand total of 30 minutes so it is not hard, if you know where to look.  The ECM is located above the right hand fuel tank.  You will need to remove the cosmetic right hand shelf to get at it.  Remember to DISCONNECT the BATTERY BEFORE beginning any work in this area. We simply removed the ECM main plug and worked with it in place. Once spliced in, the wire can be run through the hole that was previously made in the rear firewall. (Please refer to the details on installing the Water Injection System or Boost Controller for details)

If you wish to construct a Printed Circuit Board as we did, here is some more diagrams that you may find useful.

Main Component, Layout, Component Side, Actual Size

Monitor Main PCB, Trace Layout & Components

The power for this device is derived from +12 volts from the positive terminal of your car battery via a 1 amp fuse. (or some other fused source, we used the dash/fascia board light +12 volt supply line) It also needs a good ground. (Again the dash/fascia lighting ground was used)

As you can see the circuit fits quite nicely onto a small Printed Circuit Board (PCB).

Installing The Air Fuel Meter in the Lotus Esprit Dash

This is the part we were quite concerned about doing, but a quick call to our friendly Lotus dealer, reassured us that the parts we were about to potentially destroy were available as replacement parts. The cost surprisingly enough was not as expensive as we initially anticipated. 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. 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 Lotus Esprit V8 1998 onwards, workshop manual for details. We proceeded as follows:

• First remove the 2 allen screws holding the Binnacle over the dash/gauge assembly, then slide the Binnacle forward and remove it. Put it to one side and store.
• Remove the two black sheet metal screws on the left and right had edges of the dash assembly.
• Remove the two bolts and their associated lock washers that secure the dash to the main body of the car. These are tucked away at the base of the dash assembly, one on the left and one on the right. They each go through a lug on the dash assembly, and are easy to get at.
• Remove the two electrical plugs that provide power and signals to the dash, this is a little tricky as they are tight. Take your time and they will part sooner or later.
• Remove the dash assembly and 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 - Measure and Mark up The Dash and Prepare for Drilling

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 air Fuel Ration LED's (5mm T1 3/4) in the center of the cluster. These complimented out 20 Water Injector and Fuel Injector Duty Cycle LED's (5mm T1 3/4) that were above, and slightly to the left and right of the Speedometer, to provide a symmetrical "Eyebrow" effect. (Please refer to the alternate article on the other injection monitors for additional details) The measurement was not that easy, and partially done by sight, for ascetic reasons.

• Place masking tape all around the dash assembly above, to the left, and to the right of the Tach and Speedo respectively.
• Mark the outlines of the Tach and Speedo with a very fine felt tip pen. Do not press hard, it may damage the dash mask.
• Temporarily place the Binnacle on the dash assembly on the bench, and mark round the top edge. It resembles a large semi-circle, but is not even all round. However, it is quite symmetrical.
• Remove the Binnacle and store.
• Remove the Tachometer and Speedometer and store.

You will now notice there is a very narrow gap between the edge of the Tach, Speedo and Binnacle. This is where we placed the LED's.  As you will see in the photos that follow later in this article, it was a tight squeeze. At this point, depending on how many monitors you are going to install, you will need to use a mathematical compass, and a flexible curve to mark up a curve that somewhat resembles the Binnacle outline you made earlier, and blends in with the circles of the Tack and Speedo. We marked up about 4 or five combinations, and chose the one we liked the best. Once we marked it all up and were happy with the dimensions and ascetic qualities of the work, we moved on to the next step.

Step 3 - Drilling The Dash!

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 15/64 ths. of an inch. (1/64th. smaller than recommended) It was the pilot type that made a very small pilot hole prior to the actual drill size. We used a drill press at 2000 rpm. We chose the plastic type LED mounting assemblies found at Radio Shack, there is only one type for 5mm LEDs.

• Lay the 10 LED mounting assemblies along the line you marked for the meter. We slightly overlapped them to squeeze them into a shorter distance. This was done because a total of 30 LEDs needed to be installed for all 3 monitors. (The other 2 monitors are covered in other articles)
• Line them up by eye (you can do a sophisticated measurement if you like) in the correct most ascetically pleasing position. Remember to take into account any other monitors that may need to be installed.
• Mark the centers with a very fine felt tip pen.
• Drill the holes!
• De-Burr as necessary
• 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.

We then placed the LED holders in the holes we drilled, and installed the LEDs. We used a dummy/spare Tachometer and Speedometer so as not to damage the stock parts during our fabrication.

Lotus Esprit 1998 Dash, Removed from Car, Drilled with LED's Installed

The above photo shows all three monitor's LED configurations.  As you can see it is a very tight fit. This photo also shows two optional switches that we installed. One to turn the Air Fuel Monitor off, (It can be annoying for general driving) and one to turn off both the Fuel and Water Injector Monitors off. (for symmetry)

Step 4 - Wiring up The Monitor(s)

This part is pretty straight forward, if you are electrically inclined that is. The LEDs were wired to the Printed Circuit Boards (PCBs) using 2.5" wire leads. Then the PCB's were mounted directly above their respective bank of LEDs. This was done by drilling 2 small holes in the edge of the dash assembly for each board (6 total).  Then they were countersunk for the 2/56 screws that were used to attach the PCBs to the dash. (Small aluminum brackets were fabricated to finish off the installation) The following photos show the PCB's mounted and wired into the dash, with a dummy/spare Tachometer and Speedometer installed.

Lotus Esprit 1998 Dash, PCBs Installed and Wiring Complete

If you look closely you can see an extra connector in the middle rear of the above photo. This is used to take the signal wires down to their respective sensor points. This was done so we would remove the dash easily at a later date if needed.

Step 5 - Adding White Lettering, and The Finished Product

The following photos show various close ups of the dash before re-installation into the car. The white lettering is dry lettering available at any hobby shop. We added the lettering just as a finishing touch, it really is not needed.

Fuel Injector Duty Cycle Monitor PCB and Wiring Close Up

Fuel Injector Duty Cycle Monitor, LED Layout

Air Fiel Ration Meter On/Off Switch

Dash Mounted in the Car, with Binnacle Installed

We hope you find this article interesting. If you would like to receive your own meter, please go to our Gauges For Sale pages.

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