Black or Grey ICM - found a good write- up
02-07-2016, 01:12 PM
#1
Black or Grey ICM - found a good write- up
Push Start versus Computer Controlled Dwell TFI-IV ICMs
The internal circuitry of the TFI-IV ICM will have two possible arrangements; push start (PS) or computer controlled dwell (CCD).
The push start system allows for increased dwell (coil on time) when starting the engine. After engine start, the ICM internally determines coil on time (dwell) based on engine rpm (derived from the PIP signal), previous spark position and, coil charge time. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The SPOUT signal is an acronym for SPark OUTput, a digital signal generated by the PCM. The falling edge of SPOUT is ignored by the ICM. On a push start system, SPOUT only controls when the coil fires. The dwell was designed to provide either 17% or 32% excess dwell to ensure sufficient coil charge time under transient engine-acceleration conditions. Push start TFI-IV ICMs are gray in color.
A computer controlled dwell (CCD) system uses both edges of the SPOUT signal. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The falling edge of SPOUT is used by the ICM to turn the coil on. The coil on time (dwell), is therefore, entirely controlled by the PCM-generated SPOUT signal. The ICM does not internally determine dwell, it just responds to directly to SPOUT signal it receives. The PCM determined the correct dwell by measuring the time it takes for the coil to reach a predetermined current level. This has the advantage of limiting excess dwell, which significantly reduces heating in the ICM. TFI-IV ICMs that utilize computer-controlled dwell are black in color.
Last edited: Dec 14, 2010
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The internal circuitry of the TFI-IV ICM will have two possible arrangements; push start (PS) or computer controlled dwell (CCD).
The push start system allows for increased dwell (coil on time) when starting the engine. After engine start, the ICM internally determines coil on time (dwell) based on engine rpm (derived from the PIP signal), previous spark position and, coil charge time. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The SPOUT signal is an acronym for SPark OUTput, a digital signal generated by the PCM. The falling edge of SPOUT is ignored by the ICM. On a push start system, SPOUT only controls when the coil fires. The dwell was designed to provide either 17% or 32% excess dwell to ensure sufficient coil charge time under transient engine-acceleration conditions. Push start TFI-IV ICMs are gray in color.
A computer controlled dwell (CCD) system uses both edges of the SPOUT signal. The PCM calculates spark timing and outputs a rising edge of SPOUT at the appropriate time. The ICM turns the coil off whenever it sees a rising edge of SPOUT. The falling edge of SPOUT is used by the ICM to turn the coil on. The coil on time (dwell), is therefore, entirely controlled by the PCM-generated SPOUT signal. The ICM does not internally determine dwell, it just responds to directly to SPOUT signal it receives. The PCM determined the correct dwell by measuring the time it takes for the coil to reach a predetermined current level. This has the advantage of limiting excess dwell, which significantly reduces heating in the ICM. TFI-IV ICMs that utilize computer-controlled dwell are black in color.
Last edited: Dec 14, 2010
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