Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1987HI-CUBE 6.2 J, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISCCC TBI TESTS W/CODESDIAGNOSTIC CHARTSIGN SYSTEM CHECK (REMOTE COIL EXCEPT 2.5L "S" SERIES)TEST DESCRIPTION
1987 Chevrolet Hi-Cube 6.2 J, 400/M40
Test Description
1987 Chevrolet Hi-Cube 6.2 J, 400/M40SECTION Test Description
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- 1) Two wires are checked to ensure that an open is not present in a spark plug wire.
- 1a) If spark occurs with 4-terminal distributor connector disconnected, pick-up coil output is too low for EST operation.
- 2) A spark indicates the problem must be distributor cap or rotor.
- 3) Normally, there should be battery voltage at "C" and "+" terminals. Low voltage would indicate an open or a high resistance circuit from distributor to coil or ignition switch. If "C" terminal voltage was low, but "+" terminal voltage is 10 volts or more, circuit from "C" terminal to ignition coil, or ignition coil primary winding, is open.
- 4) Checks for shorted module or grounded circuit from ignition coil to module. Distributor module should be turned "OFF", so normal voltage should be about 12 volts. If module is turned "ON", voltage would be low, but above one volt. This could cause ignition coil failure from excessive heat. With open ignition coil primary winding, small amount of voltage will leak through module from "Bat" terminal to "Tach" terminal.
- 5) Checks for open module, or circuit to module. Applying 12 volts to "P" terminal or module should turn module "ON" and voltage should drop to about 7-9 volts.
- 6) This should turn module "OFF" and cause a spark. If no spark occurs, fault is most likely in ignition coil because most module problems would have been found before this point in the procedure. A Module Tester (J-24642) could determine which is at fault.
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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.