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A first-generation Honda Insight has traded its original gasoline-hybrid engine for a small Kubota diesel, with an Arduino Uno Rev3 handling part of the engine-control setup. The project’s reported fuel-economy result is striking, but it comes from a builder-run route test—not an EPA rating or an independently replicated comparison.
What engine was installed in the Honda Insight?
The conversion uses a Kubota diesel in a first-generation ZE1 Honda Insight. Hackster described the engine as a 719cc Kubota and said the builder paired it with a Saturn transmission selected for its gear ratios. Arduino’s 2024 account called it a 700cc diesel. In 2025, Equipment World identified the installed engine as a Kubota D722, rated at 20 horsepower in that account, and reported a five-speed manual transmission, automotive clutch and RHB31 turbo.
Those descriptions establish the broad layout, not a complete swap recipe: the coverage does not supply a full parts list, fabrication drawings or a step-by-step installation guide. Equipment World’s 2025 account names the D722, while Hackster’s project coverage describes the earlier 719cc engine and transmission choice.
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What does the Arduino ECU control?
The described setup uses an Arduino Uno Rev3 to read the throttle position sensor. Stepper motors, driven through stepper-driver modules, move two engine controls: the turbo boost valve and the fuel-rack limiter. The system also includes an LCD to display current positions and potentiometer knobs for manual adjustment, according to the project descriptions.
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In Arduino’s June 2024 account, adjusting those controls automatically in response to throttle position was a development goal; the account does not establish that a finished autonomous calibration strategy was implemented. Therefore, “Arduino ECU” is best understood here as a custom controller for particular engine functions, not proof that the Uno replaced every function of a complete automotive ECU. The articles do not provide ECU source code or independently validated safety and calibration data. Arduino’s project description and Hackster’s account describe the controls and manual-adjustment features.
How much fuel economy did the diesel Insight achieve?
Equipment World reported that the builder compared the Kubota-powered Insight with the original hybrid on a 60-mile rural Kansas route under identical conditions. The reported results were 70.1 mpg for the diesel conversion and 62.7 mpg for the stock Insight. The figures are the builder’s experimental results as reported by the publication, not standardized EPA ratings or proof that another build or drive would achieve the same economy. The coverage does not establish an independent replication.
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The Drive also reports the builder’s method of weighing diesel before and after the drive and gives the same 70.1 mpg and 62.7 mpg figures. It separately mentions 78.6 mpg for an earlier supercharged diesel Insight build; that is a different build and should not be treated as the result for the D722 conversion discussed here. Equipment World’s report and The Drive’s report describe the figures and test.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsIs this a complete Arduino ECU build guide?
No. The project coverage explains the controller’s general inputs and actuators, but does not publish the full wiring plan, source code, component-level parts list or a reproducible calibration procedure. It also does not independently validate the design. Treat it as a documented maker project rather than instructions for copying a road-going engine-control system.
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- BOARD AND USB CABLE INCLUDED: Comes with 1 ELEGOO UNO R3 development board and 1 USB-A to USB-B data cable; breadboard, sensors, shields and power adapter are not included, and younger learners should work with an experienced adult
The project reports do not establish present road legality, emissions compliance or long-term durability. Those questions cannot be answered from the reported road test alone.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Which Arduino board did the project use?
The project account identifies the Arduino Uno Rev3. Arduino’s product page lists an ATmega328P, 14 digital I/O pins, six analog inputs and a 16 MHz clock. Those are board specifications, not evidence that the board is suitable by itself as a complete or ready-to-install automotive ECU. Arduino Uno Rev3 product page.
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- POWER AND MODEL EXPECTATIONS - Use USB-C, 7-12 V VIN or a regulated 5 V input, share ground and drive motors or relays through suitable modules; this classic Nano V3-style board has no Wi-Fi, Bluetooth or features from Nano Every, Nano 33, Nano ESP32 or Nano R4
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