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.
1991 GMC Forward Control 5.7 K, Standard, SM465/M20FACTORY OEM SERVICE PROCEDURE
3.1L (VIN D)
- Set parking brake, block drive wheels and place transmission in Neutral or Park. Warm engine to normal operating temperature. Turn A/C off (if equipped). Ensure SERVICE ENGINE SOON light is off.
- Ground Tan/Black Electronic Spark Timing (EST) by-pass connector wire located in front of right strut tower. Connect timing light to No. 1 spark plug wire. Check timing and adjust if necessary. See V6 IGNITION TIMING table.
- Disconnect ground from EST by-pass circuit, and reconnect connector. Clear ECM trouble code.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
Comes to youSame-day available12-month warranty
Get a Free QuoteNo obligation. See pricing before you book.