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The OzTrip Car Computer

Testing a new DIY trip computer.

By Tim White, Pics by Julian Edgar

Click on pics to view larger images

Trip computers have been commonplace in luxury cars for nearly two decades. These devices provide statistical information, such as the distance travelled and fuel used on a journey, average fuel consumption and the distance that may be travelled on the fuel remaining in the tank. The OzTrip Car Computer is made by OzTechnics in Sydney. As far as we're aware, it's the first universal trip computer readily available in the aftermarket. We tested version 1.1 of the OzTrip to see whether it's an accessory worthy of a home in the modern performance vehicle.

The Unit

The OzTrip computer boasts a total of 27 functions. About one quarter of these functions provide the same information for up to three separate journeys, each of which may be monitored independently. This would be useful if you wanted to isolate a particular leg of your trip for analysis.

All the standard trip computer functions are there, including:

  • Current (instantaneous), average and peak speed,
  • Current and average fuel consumption and cost,
  • Distance to empty and the amount of fuel remaining in the tank,
  • Time remaining until the end of the trip, based on the current or average speed.

Also included in the diagnostic mode are functions for measuring injector pulse width, a "sprint timer" suitable for measuring 0-400m times and displays of the total engine hours, running time and fuel used by the vehicle.

Installation and Calibration

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The hardest part of installing and setting up the OzTrip is trying to understand the fourteen-page instruction manual. There is a lot of information but to successfully navigate your way around it requires a large pad of Post-It notes, a big pot of coffee (or a longneck) and half an hour or so. There's no contents page and the installation instructions are located somewhere near the back. The manual that was supplied did not include a wiring diagram and so a phone call had to be made to the manufacturer. Fortunately, the after-sales support was very good: the phone was manned on the weekend and our questions competently answered.

Fitting the OzTrip computer is straightforward. On the electrical side, there are only six connections to be made. The first three should be very easy to find on most vehicles: power from the battery (so the computer doesn't lose its memory when the car is switched off), ignition power (to activate the display), and earth. The fourth wire is spliced into the headlight circuit to allow the automatic dimming of the OzTrip's display when driving at night.

The remaining two wires are the data inputs for the computer and need to be spliced into the car's engine management loom. One of these inputs is the injector "on" time, obtained by attaching a wire into an injector wire coming from the ECU. The other input is from the vehicle speed sensor which is used to provide information about how far the car has travelled and at what speed it has done so. So long as you have reasonable wiring diagrams for your car, locating these two wires should only take ten minutes or so. A fuel-flow sensor is available to allow the computer to be used with vehicles running a carburettor, although we didn't test this particular unit here.

In its standard form, the OzTrip unit consists of a box measuring 135 x 110 x 35mm. The unit is very neat in appearance, although it's quite bulky and as such is unlikely to be a welcome addition to the cockpit of a modern performance vehicle. In most cases the only places it would fit are either on top of, or below the dash. For the testing we performed it was stuck on top of the dash with double-sided velcro tape. This allowed easy viewing of the display without having to look too far away from the road.

Click for larger image

If, however, the installer takes the time and effort to integrate the keyboard and LED screen into the car's dashboard, a much more aesthetically pleasing installation may be achieved. The circuitry can be hidden behind the dash so that the only space taken up on the fascia itself would be for the display screen and the four-button keyboard. The internal circuitry takes up far less room than the box dimensions would suggest, so this is probably easier to do than it first sounds.

Once the OzTrip has been wired in and fitted, the next step is to calibrate the unit so it knows the flow rate of the injectors and how to interpret the signal from the speed sensor. Calibrating the speed/distance measure requires only the pressing of a few buttons, driving the car five kilometres and then pressing some more buttons. The hardest part of this operation (as with the installation) is finding the instructions in the manual.

Calibrating the fuel-use measurement takes a fair while, although most of the job can be carried out during daily driving. The car must be filled chock-a-block with petrol and the OzTrip set to "fuel calibration" mode. The car is then driven until most of the fuel in the tank is used and the tank refilled at the pump used for the previous fill. The amount of fuel used is entered into the computer and it calculates and then stores the flow rate of the injectors. Obviously, the more fuel used during the calibration stage, the smaller the relative error will be and the more accurate the calibration procedure.

On The Road With The Oztrip

Once calibrated, the OzTrip is ready to go. It's very easy to use, with the different functions able to be called up at the press of a button. It's just a shame that the instructions complicate things so much! Each display is available in metric, Imperial or US units: a simple button-press is all that's required to change between them. There's no need to flick a switch on the back of the unit or re-calibrate it or anything like that.

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Our first attempt to use the OzTrip proved to be a failure. It was fitted to a VL Commodore with its bog-standard Nissan RB30 engine and management system. Wiring-in the computer was easy enough: the injector and speedo inputs were taken from the engine management loom near the ECU. Power and the headlight signal were drawn from behind the instrument cluster (the computer doesn't take much current). The problems began when we tried to calibrate the unit.

The first computer we tried wouldn't enter the fuel calibration mode and needed to be returned to the manufacturer. The next unit we received entered the fuel calibration mode okay but gave very strange numbers. As it transpired, the OzTrip has been developed on late model cars which use sequential injection - where each injector fires separately and/or only once per engine cycle (ie every two crankshaft revolutions). The VL, being an older car, runs group-fire injection where all the injectors fire simultaneously twice per engine cycle. It seems that the OzTrip doesn't like the smaller pulse widths of the VL's group-fire injection system.

An alternative vehicle was sourced - again a VL Turbo, but this time running MoTeC sequential injection. The calibration procedures were carried out again and this time some sensible numbers were returned. Time to go testing! A two-hour squirt through the hills around Bathurst provided all sorts of driving conditions to see whether the OzTrip could keep up with the constantly changing injector pulse width and vehicle speed.

Speed and Distance Measurement

The distance measure had been calibrated using the car's trip meter, which was found to be just about dead-accurate on one of those five kilometre freeway "speedo checks". As you'd hope, the OzTrip's distance values corresponded exactly with the trip meter throughout our testing. The calibration number achieved from the OzTrip was 800, meaning that it received 800 pulses from the VSS for every kilometre travelled. In theory then the distance measurement is accurate to within 800/1000 of one kilometre (about 0.1%).

A useful feature of the OzTrip is that it allows you to check the accuracy of the speedo itself.

The VL's odometer is driven mechanically by a cable and gearset. This type of mechanism typically remains accurate for the life of the vehicle - so long as the tyres have the correct rolling radius! However, the speedo relies on a cable-driven magnet to lift the needle against a spring - this type of mechanism can be expected to lose accuracy as the vehicle ages. Since the OzTrip calculates the vehicle speed from the speed sensor (whose signal comes directly from the cable), it's likely to be more accurate than the speedo needle.

During this particular test, the VL's speedo needle was found (at most speeds) to read about 2% lower than the OzTrip's display. One letdown here was that the speed display moves in increments of 3 km/h.......okay in most cases but not good enough if you want to accurately check your speedo.

Fuel Consumption Measurement

The fuel-use calibration yielded a number of '20' - we're not sure what that number meant in terms of fuel flow per injector on-time. What it does indicate is that the accuracy of all subsequent fuel-use measurements with the OzTrip should be accurate to within 1/20 (5%).

The new version 1.2 computer (due for release any day now) has ten times greater resolution and so will theoretically be accurate to within 0.5%. The manufacturer claims that this accuracy is enough to detect the extra fuel used on a trip when the air-conditioner is running, compared to when it is not.

So how did it go? Very well! The VL was refuelled when the computer said that 26.4 litres had been used. The pump showed it was a pretty good result.

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The OzTrip allows the amount of fuel added to the tank to be entered after each refuelling, rather than needing to be reset with a full tank. This means that useful distance-to-empty and fuel-remaining values can be displayed even if you only partially fill the tank - a feature not available on most OEM trip computers.

One of the most useful features of the OzTrip (and indeed of any trip computer) is the display of specific fuel consumption figures. Consumption figures are available in either distance travelled per unit of fuel used (km/L, miles/gallon or miles/US gallon) or fuel used per unit of distance travelled. The average fuel consumption display worked well. For comparison purposes it was handy being able to flick between km/L and miles/gallon with the press of one button. However, the current (instantaneous) fuel consumption suffered from an erratic display, even when the vehicle was being driven at a fairly steady speed.


While the measurements that the computer makes and the displays seem to be very accurate, there are some software compromises that let it all down. The most obvious is the resolution of the tachometer function: the display is limited to 120 rpm increments. While this is okay for monitoring the engine speed at high revs, it's not much use if you want to accurately set the idle speed, for example. Even though this resolution limit has been set to reduce the amount of memory required by the OzTrip (and so reduce its cost), it is a little disappointing. The speed display, as mentioned previously, has a resolution of only 3 km/h although most other functions are displayed to one or two decimal places.

A few other software glitches exposed themselves during testing. The decimal point would wander around when the computer was displaying the (also erratic) instantaneous fuel consumption. The "sprint timer" refused to work and the injector pulse width display returned a value only occasionally.

But perhaps the major letdown is that the OzTrip doesn't seem to be compatible with all cars, especially older ones running group-fire injection. Before purchasing this unit, it would be wise to check whether it's been tested on your particular vehicle or to make sure you get a guarantee that you can return it if it doesn't suit. That said, the technical support we received was quite good.

The second unit we tested had a sticky "function down" button which sometimes resulted in an erroneous value being entered into the computer or the wrong function being selected. This could be easily fixed by removing the two screws that hold the two halves of the case together and then enlarging the button-hole in the front window with a file. Things like this are, however, something that we'd expect to be improved on for version 1.2.


Click for larger image

The OzTrip Car Computer is a useful tool for things like comparing a car's fuel consumption before and after performing a modification. For those who frequently drive long distances, it would also be a useful partner for planning fuel stops. If nothing else, it's another high-tech gadget to put in your car - so long as you can find a place to fit it in! But the unit we tested had a lot of problems. Version 1.2 is due for release about now and the manufacturer assures us that all the bugs that plagued our test unit will be gone in the new model. Unfortunately we didn't have time to see whether this is the case.

The OzTrip is yet to be properly marketed - perhaps this will happen with the release of version 1.2. In the meantime, it's available direct from OzTechnics in Sydney. It's fairly easy to fit yourself or any good auto electrician would be able to do it for you in perhaps as little as an hour. The OzTrip retails for A$297 including GST, which is a fair bit to spend on a product that doesn't directly improve your car's performance. It's hard to comment whether the OzTrip represents good value as far as trip computers go since at the time of writing there are no similar products on the market against which to compare it.

An extra A$110 will buy you an interface board and software to set up a "virtual dashboard" display on a PC. The fuel-flow sensor for vehicles with a carburettor adds A$121.

Detailed information on the OzTrip Car Computer and other associated products is available from the OzTechnics website.


Rob Priestley


+61 2 9541 0310

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