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.
1998 GMC Forward Control 6.5 FFACTORY OEM SERVICE PROCEDURE
Electrical Component Locator: Miscellaneous
MISCELLANEOUS
| Component | Component Location |
|---|---|
| Accessory Junction Block (Deluxe School Bus) | On left side interior bulkhead, near relay bracket. |
| Battery Junction Block | On left side of firewall, above relay bracket. |
| Data Link Connector (DLC) (4.3L VIN W) | Below dash, near steering column. See Figure. |
| Data Link Connector (DLC) (5.7L VIN R) | Below dash, near steering column. See Figure. |
| Data Link Connector (DLC) (6.5L VIN F) | Below dash, near steering column. See Figure. |
| Data Link Connector (DLC) (6.5L VIN Y) | Below dash, near steering column. |
| Data Link Connector (DLC) (7.4L VIN J) | Below dash, near steering column. See Figure. |
| Distributor (4.3L VIN W) | On top rear of engine. |
| Distributor (5.7L VIN R) | On top rear of engine. |
| Distributor (7.4L VIN J) | On top rear of engine. |
| Fuel Heater (6.5L VIN F) | At fuel filter assembly. |
| Fuel Heater (6.5L VIN Y) | At fuel filter assembly. |
| Fuel Injectors (6) (4.3L VIN W) | On top center of intake manifold. See Figure. |
| Fuel Injectors (8) (5.7L VIN R) | On top center of intake manifold. See Figure. |
| Fuel Injectors (8) (7.4L VIN J) | On intake manifold, at each cylinder intake. See Figure. |
| Fuel Pump Prime Connector (4.3L VIN W) | Taped to fuel pump relay breakout. See Figure. |
| Fuel Pump Prime Connector (5.7L VIN R) | Taped to fuel pump relay breakout. See Figure. |
| Fuel Pump Prime Connector (7.4L VIN J) | Taped to fuel pump relay breakout. See Figure. |
| Fuel Solenoid Driver (6.5L VIN F) | On top left of engine. See Figure. |
| Fuel Solenoid Driver (6.5L VIN Y) | On top left of engine. |
| Fuel/Water Separator (Filter) (6.5L VIN F) | On rear of intake manifold. |
| Fuel/Water Separator (Filter) (6.5L VIN Y) | On rear of intake manifold. |
| Glow Plugs (6.5L VIN F) | On cylinder heads, below valve covers. |
| Glow Plugs (6.5L VIN Y) | On cylinder heads, below valve covers. |
| Ignition Coil (4.3L VIN W) | On top right side of engine. See Figure. |
| Ignition Coil (5.7L VIN R) | Top right side of engine. See Figure. |
| Ignition Coil (7.4L VIN J) | On bracket at rear of intake plenum. See Figure. |
| P/B Booster Fluid Flow & Pressure Alarm (School Bus) | On brake warning system harness, taped to dash harness at breakout to dash fuse block & headlamps switch. |
| Remote Battery Access Terminal Block | Rear of right radiator core support panel. |
| Secondary Battery | On right side of frame rail, behind engine. |
| Vehicle Speed Sensor (VSS) Buffer (6.5L VIN F) | On left side of interior bulkhead, mounted under bracket. |
| Vehicle Speed Sensor (VSS) Buffer (6.5L VIN Y) | On driver's island support, above accelerator pedal. |
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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