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HOMESERVICE MANUALSCHEVROLET1987STEP VAN P20, 7.4 W, AUTOMATIC, 475/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMCCC TESTS W/O CODESINTERMITTENT PROBLEMSPOSSIBLE CAUSE & CORRECTION
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 475/M40

Possible Cause & Correction

1987 Chevrolet Step Van P20, 7.4 W, Automatic, 475/M40SECTION Possible Cause & Correction
  • Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
  • If visual check doesn't find cause of problem, drive vehicle with voltmeter connected to suspected circuit and ground. If voltage reading changes as problem occurs, problem may be in that circuit.
  • Check for loss of trouble code memory by disconnecting TPS. Idle engine until "SERVICE ENGINE SOON" light comes on. Code 22 should be stored when ignition is turned off. If not, ECM is faulty.
  • Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch. They can cause a sharp electrical surge. Problem will usually occur when faulty component is operated.
  • Check for improper installation of electrical accessories such as auxiliary lights, 2-way radios, etc.
  • Make sure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and alternator. Ensure wire from 453 to distributor has a good ground.
  • Check ignition secondary wiring for short to ground.
  • Check circuits 419 and 451 for intermittent shorted to ground.
  • Check ECM power grounds.
  • Check for incorrect or defective CALPAK or PROM.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.