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
Leakage Test
- Open tester shutoff valve 3/4 to 1 3/4 turns from a closed position. Blow dry injector nozzle tip. Slowly depress tester lever until pressure gauge reads 1400 psi (98 kg/cm2 ). Maintain pressure for 10 seconds and observe injector nozzle tip.
- A drop may form on end of injector nozzle, but should not drop off within a 10 second period. Replace injector nozzle if drop of test fluid drops from tip during the 10 second period. See Fig 1. Release tester pressure.
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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