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DIY ECU controls Honda Insight’s Kubota diesel engine

Arduino TeamJune 18th, 2024

The Honda Insight was the first hybrid car released in North America and Honda put serious effort into making it as efficient as was practical at the time. That meant aerodynamic streamlining, which is why the first-generation Insight had very distinct covers over the rear wheels. It even had special tires with very low rolling resistance. Those factors made the Honda Insight the perfect platform for Robot Cantina’s Kubota diesel engine swap with a homemade Arduino ECU.

Engine swaps are common in the car enthusiast community, but this is an unusual one. Instead of trying to make the Honda Insight more powerful, Robot Cantina went in the opposite direction. Their project replaces the original engine with a 700cc Kubota diesel engine. That’s the kind of power plant you would typically find in industrial machines and vehicles. For reference, that engine has less displacement than any motorcycle currently offered by Harley-Davidson. 

To help this Kubota diesel engine run efficiently and cleanly in the Honda Insight, Robot Cantina needed to construct a custom engine control unit (ECU). They used an Arduino UNO Rev3 for the job. It physically adjusts the boost valve and fuel rack limiter using stepper motors through stepper driver modules. It also monitors the throttle position sensor (TPS) to determine how much the driver is pushing the accelerator. For testing and refinement, an LCD screen shows the current positions and potentiometer knobs let the driver manually set the values.

But while the driver can set boost and rack manually, the goal is to develop a formula to automatically adjust those two values in response to the TPS value. Like a production vehicle’s ECU, this will let the engine run at maximum efficiency without direct driver involvement. It will also reduce visible smog, which is an important factor for a diesel Honda Insight that the driver doesn’t want to drawing attention.