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 MANUALSCHEVROLET1986C 10 P/U 2WD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTEMISSION CONTROL SYSTEMSTECHNICAL SERVICE BULLETINSBY SYMPTOMDRIVEABILITYENGINE PERFORMANCE - ALTITUDE ADJUSTMENTPROCEDURE I
1986 Chevrolet C 10 P/U 2WD V8-350 5.7L
Procedure I
1986 Chevrolet C 10 P/U 2WD V8-350 5.7LSECTION Procedure I
To be used for the following 1986 low altitude (NA5) engines used primarily at high altitudes.
^ 4.3L Federal All Except "M" Vans
1. Advance base timing to a maximum of 4~ over specification if little or no detonation occurs at high altitude.
2a. Manual Transmission
Reset idles to original specifications on the Emission Control Information Label.
2b. Automatic Transmission
Set fast idle speed to 1800 RPM in N (neutral).
^ 5.0L/5.7L Federal
1. Advance base timing to a maximum of 4~ over specifications if little or no detonation occurs at high altitude.
2a. Manual Transmission
Do not adjust the carburetor vacuum break.
2b. Automatic Transmission
Reset carburetor vacuum break to 26~.
3. Reset base, A/C solenoid (if present) and fast idles to the specifications on the Emission Control Information Label.
^ Heavy Duty Gasoline Emission Packages
1. Advance base timing to a maximum of 4~ over specification if little or no detonation occurs at high altitude.
2. Set idle speed to specifications in accordance to Emission Control Information Label.
^ LIGHT DUTY FEDERAL DIESEL ENGINE (LH6)
The high altitude modification involves the recalibration of the fuel injection pump to a different fuel rate which will compensate for the lower air density at high altitudes. The injection pump cannot be modified on the vehicle. The following procedure should be used:
1. Remove the injection pump per Service Manual procedures. Be sure to note the relationship of the timing marks on the pump and front housing. The pump must be reinstalled to its exact previous position.
2. Send the pump to an ADS (Association of Diesel Specialists) Service Center for the altitude performance adjustment. The ADS Service Centers will be advised by Stanadyne Corporation Bulletin as to injection pump recalibration procedures.
3. Reinstall the pump per Service Manual procedure. The pump must be installed to its original timing setting. If the original timing relationship was not retained, refer to the appropriate Service Manual.
^ 4.3L Federal All Except "M" Vans
1. Advance base timing to a maximum of 4~ over specification if little or no detonation occurs at high altitude.
2a. Manual Transmission
Reset idles to original specifications on the Emission Control Information Label.
2b. Automatic Transmission
Set fast idle speed to 1800 RPM in N (neutral).
^ 5.0L/5.7L Federal
1. Advance base timing to a maximum of 4~ over specifications if little or no detonation occurs at high altitude.
2a. Manual Transmission
Do not adjust the carburetor vacuum break.
2b. Automatic Transmission
Reset carburetor vacuum break to 26~.
3. Reset base, A/C solenoid (if present) and fast idles to the specifications on the Emission Control Information Label.
^ Heavy Duty Gasoline Emission Packages
1. Advance base timing to a maximum of 4~ over specification if little or no detonation occurs at high altitude.
2. Set idle speed to specifications in accordance to Emission Control Information Label.
^ LIGHT DUTY FEDERAL DIESEL ENGINE (LH6)
The high altitude modification involves the recalibration of the fuel injection pump to a different fuel rate which will compensate for the lower air density at high altitudes. The injection pump cannot be modified on the vehicle. The following procedure should be used:
1. Remove the injection pump per Service Manual procedures. Be sure to note the relationship of the timing marks on the pump and front housing. The pump must be reinstalled to its exact previous position.
2. Send the pump to an ADS (Association of Diesel Specialists) Service Center for the altitude performance adjustment. The ADS Service Centers will be advised by Stanadyne Corporation Bulletin as to injection pump recalibration procedures.
3. Reinstall the pump per Service Manual procedure. The pump must be installed to its original timing setting. If the original timing relationship was not retained, refer to the appropriate Service Manual.
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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.