Sync Cam

Overview

Old synchronization strategy used with timing wheels with a high number of teeth without any missing/extra teeth. The camshaft sensor is used to identify the engine cycle position.

Option Description
option iconSync MX OFF
option iconSync Cam Count OFF
option iconSync Crank S Count OFF
option iconSync Cam Width ON
option iconSync Crank Divider ON. This option has a major impact on timing interrupts and changing it requires an ECU reset.
option iconMissing Set to 0 since there are no missing / extra teeth.
option iconCrank Divider Divisor for reducing crank teeth to internal teeth.
option iconCam Width Test Number of subdivided teeth that must be seen in order to synchronize.
option iconSync Teeth Copied to channel iconCrank Div Sync Err if synchronization is lost; number of good sync’s required to set channel iconStat Sync'd to ON.

If the option iconSync Cam Width option is ON, synchronization is achieved if channel iconCam Width = option iconCam Width Test when the Cam interrupt occurs.
In some ECUs this may be option iconMX Sync test.

If the option iconSync Cam Width option is OFF then synchronization would achieved if channel iconSS Tooth No = option iconCam Width Test when the Cam interrupt occurs. However, channel iconSS Tooth No is only set when option iconSync Crank Divider is OFF or during crank interrupt with the Sync Crank S Count strategy enabled. So this mode is no longer of use in recent firmware versions.

In case of loss of sync, channel iconCrank Div Sync Err is set to the value of the option iconSync Teeth and decremented for each successful Cam synchronization. When channel iconCrank Div Sync Err reaches 0, the ECU will consider the engine to be synchronized and will set channel iconStat Sync'd to ON.

channel iconPulse Acc count T1 (aka channel iconPA Count T1) is captured at start of T2 interrupt, stored in channel iconPA count1 temp. This counts T1 events (crank teeth).

channel iconCam Width receives the number of subdivided crank teeth that have occurred since the last Cam sensor event.

Examples

These are historical examples that may contain errors and have not been re-tested on modern hardware.

Historical BMW M3

135 crank teeth on ring gear, one sync pulse at 1/2 engine speed.

  • Crank Divider = 9, giving 15 internal teeth per rev. 24deg/internal tooth
  • Ign Range = 2.75
  • Fuel Teeth = 30
  • Spark Teeth = 15 (wasted spark)
  • Cam Width Test = 30 (May be channel iconMX Sync Test on some ECUs)
  • Sync Cam Width = ON (? original example reported as OFF)
  • Sync Crank Divider = ON

Nissan

360 crank teeth (high speed), 4 cylinder slots of different widths, equivalent to 2,3,5,or 5 crank teeth.

  • Crank Divider = 15, giving 12 internal teeth per rev. 30deg/internal tooth
  • Ign Range = 3.0
  • Fuel Teeth = 24
  • Spark Teeth = 12 (wasted spark)
  • Cam Width Test = 251 (? - needs confirmation)
  • Sync Cam Width = ON
  • Sync Crank Divider = ON

Use only fast falling edges for crank (T1) and cam (T2).