Ignition Timing Adjustment

The active ignition timing is a sum of "Base Timing", which is a fixed manual timing adjustment, and either a prebuilt or custom timing map.
  • For a prebuilt timing map, which is made for a specific engine, the ignition will adjust timing based on changes to speed and load (if a manifold pressure sensor is present). The map is also adjusted based on user-entered elevation and fuel specific gravity, if known. The Base Timing offsets the timing map some amount if desired.
  • For a custom timing map, the user specifies an RPM Advance, which adjusts timing based on changes to RPM, and a Load Advance, which adjusts timing based on changes to load. The Base Timing is also used to quickly adjust the timing up or down. A custom map can also be used for fixed timing by setting the RPM advance values to the same advance.
The total timing is limited to the range 5 to 60 degrees BTDC, and if out of range it will be clipped.

BASE TIMING


Base Timing is a manual timing adjustment that is fixed. The purpose of Base Timing is to allow the operator to quickly advance or retard the timing in small increments without having to modify the RPM Advance, Load Advance, or map settings.

Base Timing can be positive (timing advance) or negative (timing retard). Base Timing adjustments increment in 0.25° steps. Base timing is adjusted on the Timing Display page (Pg. 443), which is accessed by clicking on the small timing graph on the Ignition Home screen.


ICM Timing Display screen

If a prebuilt timing map is selected in ignition setup, the base timing will start at 0 degrees. The base timing can still be adjusted to raise or lower the timing. If in a prebuilt timing mode, it is not recommended to have base timing outside the range +/- 5 degrees.

SELECTING A TIMING MAP

A timing map is normally selected during ignition setup at step 4. To change after setup, go to "Setup and Testing", then "Timing Map / RPM Advance / Load Advance". On the left side of this screen the user can select a prebuilt timing map for this engine, or can select "Custom" for a custom map.


Timing map selection screen with "Custom" selected

CUSTOM MAP


If not using a built-in timing map, RPM Advance is used to automatically adjust ignition timing for changes to engine speed. RPM Advance is configured during the setup process but can be adjusted at any time through the above screen. Security access of Setup or Engineering is required.

For the low RPM timing:
  • Set the low RPM value to the cranking RPM or at the lower range of operating RPM, whichever is desired
  • Set the timing the ignition should be running at that specific RPM
For the high RPM timing
  • Set the high RPM value to the maximum operational RPM
  • Set the timing the ignition should be running at that specific RPM

The timing will automatically be interpolated between the two specified RPM values. If the engine speed runs below or above the RPM values, the timing will clip to those respective values.

Timing is typically advanced, or increased, from TDC as RPM increases.

LOAD ADVANCE


If not using a built-in timing map, Load Advance is used to automatically compensate ignition timing for changes in engine load. In order to configure and utilize the Load Advance feature, a manifold pressure sensor (EMIT #13207) is required. The manifold pressure sensor can be directly wired to the ICM or wired to an AFRC or Governor, if equipped. Load Advance is configured on the Load Advance screen (Pg. 431) and requires Engineering security access. This page can be accessed from the "Timing Map Selection" screen if "Custom" is chosen, by selecting the "Load Advance" button.

When setting up Load Advance, use the “+/–” button in the keypad to switch between pressure units and advance or retard timing. For pressure, positive units are in PSI boost, and negative units are in “Hg vacuum. For timing, positive units are timing advance and negative units are timing retard.

For the low load timing:
  • Enter the manifold pressure value that represents low or moderate load on the engine
  • Enter the degrees of additional timing advance or timing retard at this load point
  • This is typically left at “0.00°”
  • Enter the percent load of the engine at this manifold pressure
For the high load timing:
  • Enter the manifold pressure value that represents high load on the engine
  • Enter the degrees of additional timing advance or timing retard at this load point
  • Enter the percent load of the engine at this manifold pressure

When setting up Load Advance, keep in mind that the timing values are in addition to existing RPM Advance and Base Timing settings. For example, timing may already configured, but Load Advance is required to adjust timing for load swings. A typical Load Advance setup may have 0.0° at low load and -5.0° timing retard at high load.

The Load Advance screen (Pg. 431) also allows a load calculation to be configured. The “Percent Load” values provided will calculate the load based on changes to the manifold pressure. These values are for display only and are intend to give the user an idea of the current load on the engine.




Load Advance Setup Screen

INDIVIDUAL CYLINDER TIMING

The timing for each cylinder can be offset from the Total Timing of the ICM. Timing offsets are in increments of 0.25° of either timing advance or timing retard. An individual cylinder can be offset at most +/- 3.0° from the global timing value. Like global total timing, an individual cylinder’s total timing will be clipped to the range 5° - 60° BTDC.

Cylinder offset timing is set on the Individual Cylinder Information screen (Pg. 442) of each cylinder, which is found by selecting the desired cylinder on the Cylinder Information screen (Pg. 440). A security access mode of Setup or Engineering is required to adjust the timing.


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