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Home >> Saturn >> 1994 >> SW2 Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Basic Ignition System Checks (C-4) >> HEI-Est Distributor >> Tach Pulse (RPM) Signal
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Tach Pulse (RPM) Signal

  1. Connect a scan tester to the ALDL diagnostic connector. RPM should be indicated on tester when engine is cranked or running. If scan tester is unavailable, tach pulse (RPM reference from ignition module) will be indicated as a voltage signal on a DVOM (with a minimum 10-megohm input impedance) when DVOM is touched to circuit No. 430 PCM terminal with engine cranking.
  2. A tach pulse signal may be simulated (to test PCM response) by connecting a test light in series between battery and circuit No. 430 PCM terminal. Each time test light is touched to and removed from circuit No. 430, PCM will see this as a tach signal. For circuit and terminal reference, see appropriate schematic under NO START - ENGINE CRANKS OKAY.
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