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 MANUALSCHEVROLET1985S10/T10 BLAZER 4WD L4-151 2.5LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTIGNITION SYSTEMIGNITION TIMINGADJUSTMENTS
1985 Chevrolet S10/T10 Blazer 4WD L4-151 2.5L
Ignition Timing: Adjustments
1985 Chevrolet S10/T10 Blazer 4WD L4-151 2.5LSECTION Adjustments
NOTE: Refer to the underhood Vehicle Emissions Control Information label. Follow all instructions on the label.
IGNITION TIMING ADJUSTMENT
- Block wheels and warm engine to normal operating temperature.
- With ignition off:
- Connect timing light to number 1 cylinder.
- Place Electronic Spark Timing system in Bypass Mode by jumpering terminals "B" to "A" at the Assembly Line Data Link (ALDL) connector.
- Start the engine, and aim the timing light at the timing mark. The mark on the pulley should line up with the timing mark, adjust if necessary. Specifications
- Turn off the engine, remove the timing light, remove jumper from ALDL connector.
- Recheck Idle Speed, adjust if necessary.
NOTE: Jumpering the ALDL connector will set a trouble code and cause the check engine light to flash. After checking timing, check and clear trouble codes.
Spark Plug Wire Routing:
TIMING MARK:
IGNITION TIMING ADJUSTMENT
- Block wheels and warm engine to normal operating temperature.
- With ignition off:
- Connect timing light to number 1 cylinder.
ALDL Location - C2:
ALDL Connector:
- Place Electronic Spark Timing system in Bypass Mode by jumpering terminals "B" to "A" at the Assembly Line Data Link (ALDL) connector.
- Start the engine, and aim the timing light at the timing mark. The mark on the pulley should line up with the timing mark, adjust if necessary. Specifications
- Turn off the engine, remove the timing light, remove jumper from ALDL connector.
- Recheck Idle Speed, adjust if necessary.
NOTE: Jumpering the ALDL connector will set a trouble code and cause the check engine light to flash. After checking timing, check and clear trouble codes.
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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.