Regal V6-260 4.3L DSL (1985)
Engine Speed Signal: Description and Operation
The ECM monitors engine RPM through a ``tach'' lead from the Delcotron ``R'' terminal. Engine RPM is used to determine EGR solenoid dwell
period and to control TCC engagement. The ``Check Engine'' lamp will remain illuminated whenever the ignition key is on and the engine speed signal is
less than 400 RPM. However, if the ``tach'' signal is lost, the light will remain illuminated even after engine speed exceeds 400 RPM.
