AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 182)

Page 182 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
Accel dTPS – Displays the current delta TPS value
Accel dTPS Latched – Displays the last activated delta TPS value
Accel Trigger Count – Displays the current number of times the accel pump has been
triggered. Resets at 255.
Accel Fuel +Max – Displays the current allowable size fot the accel pump based on the current
injector PW and Accel Limit value
Accel Fuel – Current calculated Accel Fuel value in milliseconds
Ignition Tuning Theory
Some basic terms, concepts and recommendations should be understood prior to beginning the
ignition tune.
Spark Plugs
Spark plug selection affects engine performance. On forced induction engines, it is critical that
the proper heat range and gap is used. Heat range refers to the ability of the spark plug to
conduct heat away from the electrode to the engine. A plug that has high thermal conductivity
has a short insulator that comes in contact with a large portion of the metallic plug shell. This
large area allows the combustion heat to be carried through the plug shell to the cooling jacket
of the cylinder head. In the case of a hot plug, the insulator is recessed deeply into the plug
shell with minimal contact to the shell. The plug has low thermal conductivity due to the lack of
contact with the shell. The nose of the insulator should operate at between 400
– 850 degrees
C. Temperatures above 400 degrees C are desirable because at higher temperatures deposits
from carbon, lead or soot are burnt off. Temperatures of 850 degrees C and over should not be
exceeded because this is typically the point where detonation or auto ignition can occur. Lower
heat range plugs have a higher resistance to auto ignition while higher heat range plugs have
less tendency to foul.