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Home >> Buick >> 1995 >> Roadmaster Base >> 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 DLC. RPM should be indicated on tester when engine is cranked or running. If scan tester is not available, 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 PCM terminal circuit No. 430 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 PCM terminal circuit No. 430. 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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