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 MANUALSCHEVROLET1987FORWARD CONTROL 4.8 T, AUTOMATIC, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMFUEL INJECTION SYSTEM - TBITROUBLE SHOOTINGPRELIMINARY CHECKS
1987 Chevrolet Forward Control 4.8 T, Automatic, 400/M40
Preliminary Checks
1987 Chevrolet Forward Control 4.8 T, Automatic, 400/M40SECTION Preliminary Checks
Check or perform the following items before beginning diagnosis of fuel injection system:
- Check vacuum hoses for cracks, kinks, and proper routing.
- Check for air leaks at throttle body flange and at intake manifold.
- Check ignition system.
- Check all electrical connections and terminals (including battery).
- Perform DIAGNOSTIC CIRCUIT CHECK. See GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
- If engine cranks but will not run, see CHART A-3 in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
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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.