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I have a honda jazz with an i-DSI engine and when I did a coil check by unplugging the coils one by one, all four coils in the front does not affect the engine rpm when removed, except the 4 in the back. Is it a normal characterisric for an i-DSI engine or do I have bad coils?

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Honda i-DSI engine uses dual spark plugs per cylinder. So, I assume you have a 4-cylinder engine with 8 spark plugs, 2 per cylinder.

One of the spark plug initiates the combustion, the other sparks later to complete the combustion.

If you unplug the spark plug that completes the combustion, you should see little difference, only slightly lower power and slightly worse fuel consumption. Remember that an ordinary gasoline engine does not have this second spark plug.

If, on the other hand, you unplug the spark plug that initiates the combustion, you should definitely see harmful effects, because only the plug that sparks too late is sparking.

Sounds just like I would expect a Honda i-DSI or for that matter any dual spark plug per cylinder engine to work.

(Edit: changed "remove" to "unplug"; you shouldn't obviously completely remove a spark plug...)

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    It is not the only engine to have had two spark plugs per cylinder... Alfa did it amongst others... – Solar Mike Jul 7 at 7:11
  • A 6 cyl engine had valves fail on one cylinder in a race, so they removed the plug and drilled holes in the piston so they could run on 5 and reduce the pumping losses... – Solar Mike Jul 7 at 7:14
  • Sooo.. I guess its normal behavior for this type of engine. Btw I was talking about the ignition-coils not the spark plugs, since i know the plugs are good cuz i just got it replaced, so i was then checking each indivual coils by disconnecting their wires and observing if the rpms would drop indicating they are still good, since i cant afford to replace all of them cuz they are expensive as hell. I guess this type of checking method is not effective for this type of engine. Thanks tho, it helped – john natalis Jul 7 at 7:29

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