Procedure II

To be used for the following 1986 high altitude (NA6) engines used primarily at low altitudes.

^ 4.3L Federal All Except "M" Vans

1. Retard base timing up to 4~ from specification if detonation occurs at low altitude.

2a. Manual Transmission

Reset idles to specifications on the Emission Control Information Label.

2b. Automatic Transmission

1. Set fast idle speed to 2200 RPM in N (neutral).

2. Reset all other idles to specifications on the Emission Control Information Label.

^ 5.0L/5.7L Federal

1. Reset base timing to specification on the Emission Control Information Label.

2a. Manual Transmission

Do not adjust the carburetor vacuum break.

2b. Automatic Transmission

Reset carburetor vacuum break to 24~
3. Reset base idle speed to specification on the Emission Control Information Label.

4. Reset fast idle speed to specification on the Emission Control Information Label.

^ LIGHT DUTY FEDERAL DIESEL ENGINE (LH6) Vehicles designed for principal use at high altitude that perform satisfactorily at low altitude without excessive smoke levels need not be adjusted for extended operation at low altitude.

DEALERS AND CUSTOMER INFORMATION Owners of the 1986 high altitude vehicles taking up permanent residence in one of the low altitude
counties, should be encouraged to have these adjustments performed when vehicles are brought in for service. After performing these adjustments, dealers should advise customers that, IF THE VEHICLE IS RETURNED TO CONTINUOUS, HIGH ALTITUDE OPERATION, THE ENGINE SHOULD BE RE-ADJUSTED TO HIGH ALTITUDE SPECIFICATION PER THE CORRECT CHASSIS SERVICE MANUAL FOR IMPROVED PERFORMANCE. IF RE-ADJUSTED TO HIGH ALTITUDE SPECIFICATIONS, THE SUPPLEMENTAL LABEL SHOULD BE REMOVED.