Disabling i-Stop Feature

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I’ve been wondering what i-Stop actually entails, thinking that the engine simply shuts down while you are sitting at a standstill, and then the starter-motor kicks in once you’re ready to proceed to get the engine going again.  Apparently Mazda’s Idling Stop Technology¹ is much more sophisticated than conventional idling stop systems that depend so much on the starter-motor, and I didn’t realize that they’ve adapted it to Fiat’s engine…

While conventional idling stop systems rely on a starter motor to restart the engine, Mazda’s i-Stop restarts the engine through combustion; fuel is directly injected into a cylinder while the engine is stopped and ignited to generate downward piston force. The result is a quick and quiet engine re-start compared to other systems and a significant saving in fuel.

To restart the engine by combustion, the compression-stroke and expansion-stroke pistons need to be stopped at exactly the correct positions to create the right balance of air volumes. Mazda’s i-Stop ensures precise control over the piston positions during engine shutdown. With all the pistons stopped at the optimum positions, the system then identifies the initial cylinder for fuel injection. It injects fuel and ignites it to restart the engine. Even at extremely low rpm, cylinders are identified for sequential ignition, making the engine quickly pick up to idling speed.

These technologies enable the system to restart the engine with exactly the same timing every time, to enhance fuel economy, and to deliver smooth and comfortable acceleration for the driver at restart. The restart takes place in a mere 0.35 seconds (internal measurement on vehicle with automatic transmission), which is about half of the time taken by conventional starter-motor idling stop systems.

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Perhaps many of those that have this feature don’t realize that the starter-motor isn’t working extra duty after all, but regardless wish to disable i-Stop and forego the 8% savings in fuel economy².  Other than a programming change via the OBDII port (using a ELM327 diagnostic scanner and figuring out what to change), I’ve been reading other little tricks that will disable the feature that is incorporated into the 124 Spiders built for certain regions of the world.   I’m personally not familiar with the feature in the U.S., so I assume North American vehicles in general don’t get it, although Fiat has specified that Mazda install their “Start-Stop” heavy-duty battery in all Spiders.

  • Pressing the i-Stop button once the vehicle is started will disable the feature for the current trip.
  • If the windshield defog is activated, i-Stop will not engage, so if that function survives through the restart procedure, that might be a viable alternative.
  • A permanent method was described in the German Mazda-3 forum and ronnie has provided the Google translation:

In the hood lock is a small switch, which mediates whether the hood is open for maintenance purposes. The i-Stop is disabled for maintenance purposes. The switch is fixed with a screw and has a plastic pin that sits in a bore. Loosen the screw, turn the switch so that the pin sits next to the hole and screw on again. Now it is no longer pressed with the hood closed and the i-Stop is permanently deactivated!

Since there is [no ‘hood open” light in the cluster], there is also no error message!

¹    quote and illustration courtesy of Mazda
²    (under Japan’s JC08 mode test cycle, per Mazda)

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