Toyota Hilux Diesel-Gas tachometer converter

Project updated 24.04.2004


My friend Ripa did diesel conversion for his Toyota Hilux. Ripa did not find a way to get Hilux original tachometer to work with new diesel engine 2L-T. Ripa asked me help. After some research tachometer is now working.


Converter implementation

Toyota 2L-T engines injector pump contains tacho generator. Tachogenerator gives nice solid sine signal. Problem was / is that no data is available how many pulses / engine revolution tachogenerator produces. First guess for 4-cylinder gas tacho divisor drive was 24 or 25. Tests during installation gave divider value 20. 20 are good value until better information is available.

Coil ignition tachometer drive is basically simple task, give voltage spike on every ignition event. Problem however is that no specification is available how high and how long pulse should be for particular tachometer implementation. To get this solved was the most work in this project.

First try was 0-12V 2ms pulse. No cheese with this.

Second try was simple flyback circuit generating 200V 10us spike. Also no cheese with this one.

Third try was more systematic test with 100Hz signal. This was produced with variac and rectifier. Tests showed that 18V p-p is the trigger threshold. So rather long pulse and over 18V was needed for Hilux tachometer drive. You can see the implementation from schematic


Schematics can be found here

No PCB is made for this project. Picture of prototype board can be found here

Software can be found here

Few lines of software needed for this converter is written with Hi-Tech c. Because we did not know correct divider I made software to read divider from portb. There is also jumper J5 for test tachometer without tacho generator input. When test jumper is installed converter generates 500 Hz (1000pulses/s) input test signal.