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.
1987 GMC Forward Control 4.8 T, StandardFACTORY OEM SERVICE PROCEDURE
Typical Oscilloscope Patterns: Notes
NOTE:
A special adapter placed on top of the coil cap assembly is commonly used to view the HEI secondary pattern. Refer to the scope manufacturer's instructions.
Attach scope secondary pick-up and adapter (if equipped). Connect pick-up to No. 1 spark plug wire. Connect primary pick-up to "TACH" terminal at distributor connector plug. See Figure.
Factory Service Tools
Use the Manual With the Right Hardware
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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.