AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 22)

Page 22 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
engine position. Distributed spark systems also rely on a mechanical link between the engine
and ignition output, which adds another dimension of unreliability-and to a minor extent-
inaccuracy in timing. In addition to these problems, distributed spark systems typically produce
the least intense spark of all ignition systems. The time to achieve full charge diminishes as
engine speed increases; therefore the coil charge is reduced as a function of RPM. In spite of
the potential problems with distributed spark systems, they have been used successfully for
many years on high-performance engines. Distributed spark ignition systems respond well to
spark amplification within their design limits.
Wasted Spark
Wasted spark systems employ one coil for two cylinders. The term “wasted spark” comes from
the fact that each plug fires every engine revolution. On a 4-cycle engine, the piston is at Top
Dead Center (TDC) two times for every cycle; once for firing and again during the overlap
phase. The wasted spark coil fires one plug Before Top Dead center (BTDC) and another plug
just before the overlap phase (at the latest part of the exhaust stroke before the exhaust valve
closes). Wasted spark systems have a higher potential for spark intensity because the duty of
charging and discharging is split between the coils, which allows for more charge time per coil.
Additionally, wasted spark systems build up less heat in the coil, making it more reliable.
Wasted spark systems have been in use sin
ce the mid 80‟s on GM cars and on motorcycles for
considerably longer than that. There are no moving parts, no complicated relationships with a
cap and rotor to maintain, and they deliver very accurate spark timing. Furthermore, multi-
channel spark amplification systems to enhance spark duration or intensity are available for
wasted spark ignition systems.
Direct Fire
Direct fire systems employ one coil on each spark plug and is the most reliable system used
today, (this type of system is used on most modern cars). Each coil fires sequentially in the
cylinder firing order. The charge time for each coil is twice as long as those of a wasted spark
system, which allows direct-fire, coil manufacturers to build compact, lightweight coils that retain
sufficient spark energy. There are no moving parts to wear out and no HT leads that will
deteriorate. The lack of HT leads in direct fire systems is a major advantage for an EFI-
equipped car because there is a very low incidence of noise due to leaking or improperly routed
wires. There have been incidences of the terminal from a direct-fire coil (that attaches to the
spark plug) cracking and subsequently causing Radio Frequency Interference (RFI) or “noise” to
the ECU. This will cause engine operation problems, but it should be noted that these cases
are extremely rare.
Harness Connections
Coil Harness Connections
Name Wire
Wire
Color Stamping
Coil 1 Output 22 Dk Blue IGN 1
Coil 2 Output 22 Dk Blue IGN 2