This factory service and repair manual for the 1986 GMC W7500 Forward has two turbocharged diesels to account for, and the gap between them is wide: an 8.4L inline-six of 513 cubic inches and a 5.8L inline-six of 353. Both go into the low tilt straight truck in the W7R042 trim. Since the two engines differ substantially in size, the specifications and torque values are stated per engine, and the diagnostics follow each on its own terms.
Engines covered
- 8.4L inline-six (513 cu in) — turbocharged, diesel
- 5.8L inline-six (353 cu in) — turbocharged, diesel
Body styles covered
- Straight truck, low tilt
Trims covered
- W7R042
Known issues on the 1986 W7500 Forward. No recalls are recorded federally for the 1986 W7500 Forward, and NHTSA holds no owner complaints for the model year. That leaves the manual to cover both diesels on their merits, the 513 cubic inch 8.4L and the 353 cubic inch 5.8L, each turbocharged, with the procedures, specifications, torque values, wiring diagrams and diagnostics that keep either one serviceable.
