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.
1990 Chevrolet Forward Control 7.4 N, Automatic, 3L80-HD/M40FACTORY OEM SERVICE PROCEDURE
Ignition Coil Resistance (Internally Mounted)
- Turn ignition off. Remove the distributor cap and coil assembly. Turn cap upside down. Set ohmmeter to low scale. Connect leads to coil BAT and TACH terminals. See Fig 1. If resistance exceeds zero, or nearly zero, replace ignition coil.
- Set ohmmeter on high scale. Connect one lead to coil secondary terminal and the other lead first to TACH terminal and then to ground terminal. If resistance reading in BOTH instances is infinite, replace ignition coil.
Factory Service Tools
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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.
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