Fuel Rack Position
The fuel rack is the rod in an in-line injection pump that rotates the pumping element of every cylinder at the same time; its position determines the amount of fuel delivered per cycle. With the rack fully closed the fuel is cut off, with it fully open the maximum fuel goes through. This is the element the governor actually moves.
On an engine with a mechanical governor the chain is as follows: the throttle lever changes the pre-tension of the governor spring, and the governor positions the rack. That is, the throttle lever does not directly set the fuel quantity, it sets the governor's target. When the load changes, the governor moves the rack by itself at the same throttle position.
- Rack position is almost directly proportional to the torque the engine produces; that is why in some systems it is used as a load indicator.
- A sticking rack leads both to speed oscillation and to the engine being unable to recover under load.
This distinction is decisive for AXI kits: the GS740 and GS740-3P do not touch the rack, they pull the throttle lever with a cable. Consequently, even after the kit is fitted, the element that determines the fuel quantity is the engine's own governor and rack. Stopping the engine also happens by closing the rack or with the fuel shut-off solenoid, not by pulling the throttle lever to idle.
Context in which this term is used: Electronic speed and throttle control on diesel engines