The popular 24+TDC configuration from the Toyota, Mazda Rotary, Honda etc. engines can be used in many different ways. The 24 tooth gear gives a pulse every 30 degrees of crank rotation. Some distributor encoders use a combination of TDC and Home triggers with this gear. Below are explanations of the different types and also the modifications that could improve stability and simplicity in wiring when using the Spitronics ECU’s.

Toyota usually have one tooth on a separate space in combination with two sensors. Each sensor provides a home pulse on a different revolution of the engine. This allows the ECU to sink injection and timing to a specific stroke of the engine every time it starts. This setup requires three inputs from the ECU. The ECU could sync in one revolution. Some ECU’s have only one home input which means then engine may have to turn sometimes two revolutions before crank angle can be established.

Using the sensors without modifications is possible but due to the differences in sensor that the Spitronics ECU’s have to cater for, this one needs a bit of external filtering. See the drawing below.

The Reference wire is usually common in these encoders. The older ones used these colours and white is common. Then Crank and Home are connected to P1 pin 12 and 11 respectively. Check the drawings for wire colours. Usually we use only Home1 sensor. You may add the Home2 sensor on the same connection as shown in optional jumper settings. If the sensor signal is strong this will work perfectly. If it is week then it cannot be used. This method is only for Split sequential injection. For full sequential only use Home1 sensor. If you find interference during cranking or at higher revs add the optional resistor A to the circuit. Resistor B is seldom required due to constant excitement of the crank sensor. If it is possible, move the sensors closer to the tooth gears but they must not touch. Ensure a paper can move between them easy. It they touch it will make more interference.

These 24 tooth trigger wheels can be modified and used with different firmware if it is available for that product. Make sure about this before you proceed. This means that the home sensors are not required. The interference with the 24 tooth gear is very little as the sensor is constantly exited by the many teeth. If you are going to fuel the engine with Split-sequential injection you may grind out two opposing teeth on TDC and BDC. This will then convert to the 12-1 programs which is available. NB. Engine must be on TDC in the drawing below. Note that the Home pulses on the Toyota CAS units have a gradual build-up of metal in front of the sensor as it turns. This is to prevent interference on the sensor due to no excitement. The Mercury2 style input cannot sense this configuration successfully so you may need to modify the sensor as described below.

If you want to do full sequential then only take 1 tooth out under the sensor when the engine is on TDC. The firmware for this gear is Program 84 24-1 Dizzy 4Cyl Full/Seq. It is not popular and may be supplied on request. See the drawing below.

Mazda Rotary engines are 2 stroke and don’t require a home pulse. They opted for the pattern below.

Using the sensors without modifications is possible but due to the differences in sensor that the Spitronics ECU’s have to cater for, this one needs a bit of external filtering. See the drawing below.

The older ones used these colours. Then Crank and Home are connected to P1 pin 12 and 11 respectively. Check the drawings for wire colours. If you find interference during cranking or at higher revs add the optional resistor A to the circuit. Resistor B is seldom required due to constant excitement of the crank sensor. If it is possible, move the sensors closer to the tooth gears but they must not touch. Ensure a paper can move between them easy. It they touch it will make more interference.

Honda use a 3 level crank angle sensor like below. The 4-point wheel is handy to start quickly because spark does not need to be synced to the stroke of the engine due to the distributor cap that does the syncing. Spitronics only use the crank 30° and the Home 720° sensors.

Using the sensors without modifications is possible but due to the differences in sensor that the Spitronics ECU’s have to cater for, this one needs a bit of external filtering. See the drawing below.

The older ones used these colours. Then Crank and Home are connected to P1 pin 12 and 11 respectively. Check the drawings for wire colours. If you find interference during cranking or at higher revs add the optional resistor A to the circuit. Resistor B is seldom required due to constant excitement of the crank sensor. If it is possible, move the sensors closer to the tooth gears but they must not touch. Ensure a paper can move between them easy. It they touch it will make more interference.

These 24 tooth trigger wheels can be modified and used with different firmware if it is available for that product. Make sure about this before you proceed. This means that the home sensors are not required. The interference with the 24 tooth gear is very little as the sensor is constantly exited by the many teeth. If you are going to fuel the engine with Split-sequential injection you may grind out two opposing teeth on TDC and BDC. This will then convert to the 12-1 programs which is available. NB. Engine must be on TDC in the drawing below.

If you want to do full sequential then only take 1 tooth out under the sensor when the engine is on TDC. The firmware for this gear is Program 84 24-1 Dizzy 4Cyl Full/Seq. It is not popular and may be supplied on request. See the drawing below.