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I bought a timing light to check my spark timing; my vehicle is a 93' Mazda Miata and I am rotating the Cam Angle Sensor to advance or retard my timing. When I first used my timing light the engine was warm but not quite hot. I found out that my timing was retarded by about 3 degrees so I advanced it back to 10 degrees BTDC and took it for a test ride and after I got back I rechecked my timing and it seems to have advanced about 3 degrees so I retarded it back to 10 degrees. Now after the vehicle has cooled down I go again to test my timing and it seems like it is retarded back to where it was.

Now my questions are

  • why does the timing advance when the engine is hot? The rpm and engine load is the same so I don't think it has anything to do with that.

  • When should I adjust the timing? when it is hot or while it is warmed up?

  • When testing the timing while the engine is hot, the firing even seemed to be at a random angle every time like sometimes it was 12 others it was 14 does that signify anything?

  • Are you checking the timing with any vacuum advance disconnected? I'm not sure it has one, but you shouldn't check it with it connected because it will cause bad readings. – Pᴀᴜʟsᴛᴇʀ2 Apr 30 '17 at 0:56
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    Did you jumper the TEN and GND terminals at the diagnostic connector? The engine should be at operating temp and idle speed should be at 850 rpm when adjusting timing. – Ben Apr 30 '17 at 3:31

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