Honda Insight Receives a Tiny Diesel Engine Swap with DIY Arduino ECU

Go to your local “cars and coffee” meetup and ask around about engine swaps. You’ll likely find one person who dropped an LS1 into a Mazda Miata to get crazy horsepower-to-weight numbers and another person who put an SR20DET in an old Datsun for similar performance reasons. What you probably won’t find is a car with a tiny diesel engine intended for farming and construction equipment. That’s why we’re so titillated by Robot Cantina’s ongoing quest to swap a Honda Insight engine for a little 719cc Kubota diesel engine.

This is a first-generation (ZE1) Honda Insight that already came with an itty bitty 1.0L three-cylinder gasoline engine from the factory as part of the hybrid electric drivetrain (the first in a production car in North America). The ZE1 was very slow, but also incredibly efficient. Thanks to the hybrid drivetrain and aerodynamic streamlining, it could achieve 61mpg (US gallons) on the highway — significantly better than the 41mpg of the first-gen Toyota Prius that would hit the market a few months later.

Robot Cantina decided that the ZE1 would be the perfect platform for their swap, because the new Kubota diesel engine has a displacement of just 719cc and doesn’t produce enough power to move a heavier, less aerodynamic vehicle around safely on public roads. They originally put this engine in an old Saturn SC, but that vehicle was falling apart and proved to be more hassle than it was worth. So now they’re in the process of putting that engine in the Honda Insight.

Mounting the engine was straightforward, as it is very small and the ZE1’s engine bay has plenty of room for it. Robot Cantina paired the Kubota engine with the transmission from the Saturn, which had more suitable gear ratios than the Insight’s transmission.

This Kubota engine is meant for grunt work, so it can run with very little electronic sophistication. But Robot Cantina wanted the Insight to perform efficiently without spewing huge clouds of black smog all over the place. That led them to the creation of a DIY ECU (engine control unit) for managing the engine.

Robot Cantina created this ECU using an Arduino Uno Rev3 board. The only real input is the TPS (throttle position sensor), which tells the ECU how far the driver is pushing the accelerator pedal. In response, the Arduino adjusts two things: the turbo boost valve and the fuel rack limiter. Those work together to influence the air-fuel mixture, which is critical for efficiency and performance. The Arduino is able to physically make the adjustments using stepper motors.

The driver can use a pair of potentiometer knobs to adjust the boost and rack values manually, but Robot Cantina’s goal is to come up with an algorithm that lets the ECU set values automatically based on throttle position for maximum efficiency. This is a long process, so be sure to follow along on the Robot Cantina YouTube channel.