Emissions - Engine Performance Altitude Adjustments
85chevy10Number: 85-46
Section: 6E
Date: Mar., 1985
Subject ALTITUDE ADJUSTMENTS FOR
ENGINE PERFORMANCE
Model and Year ALL 1985 TRUCKS WITH GASOLINE ENGINES
TO: ALL CHEVROLET DEALERS
The adjustments specified within this bulletin are intended for vehicles currently in customer use and do not apply to new vehicles in dealer inventory. The adjustments are provided for the purpose of vehicular performance and customer satisfaction of emissions specifications for the involved vehicles.
This bulletin has been divided into two (2) procedures. Procedure I is applicable to Low Altitude (NA5) trucks taking up permanent residence in a high altitude county. Procedure II is applicable to High Altitude (NA6) trucks being used primarily in low altitude counties.
The only exception is the California closed loop (Computer Command Control) system which is self compensating for altitude. Applicable California engines which require no adjustment are th 1.9L, 2.8L, 4.3L, 5.OL, and 5.7L.
VEHICLE EMISSION CONTROL INFORMATION UPDATE LABEL
Anytime a vehicle is modified for an altitude change, a label is needed. The label should be affixed in a readily visible position in the engine compartment and where possible beside an existing Emission Control Information (Tune-Up) Label and should not be affixed to any equipment that can be easily detached from the vehicle.
Prior to installation of this label, the dealer code number and date of modification must be typed (with or without ribbon) or lettered with ball-point pen in the space provided.
FIGURE 1:
Label, P/N 14091953, is applicable for low altitude vehicles being used primarily at high altitudes (see Figure 1).
FIGURE 2:
Label, P/N 14091954, is applicable for high altitude vehicles being used primarily at low altitude (see Figure 2).
The labels can be ordered directly from WDDGM.
HIGH ALTITUDE COUNTIES
DEALERS AND CUSTOMER INFORMATION
Owners of the 1985 low altitude vehicles taking up permanent residence in one of these high 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, LOW ALTITUDE OPERATION, THE ENGINE SHOULD BE RE-ADJUSTED TO LOW ALTITUDE SPECIFICATION PER THE CORRECT CHASSIS SERVICE MANUAL FOR IMPROVED PERFORMANCE. IF RE-ADJUSTED TO LOW ALTITUDE SPECIFICATIONS, THE SUPPLEMENTAL LABEL SHOULD BE REMOVED.
PROCEDURE I
To be used for the following 1985 low altitude (NA5) engines used primarily at high altitudes.
Light Duty Federal Emission Packages
^ 1.9L Federal
1. Advance base timing to a maximum of 4~ over specification if little or no detonation occurs-at high altitude.
2. Adjust idle speed to specifications on the Emission Control Information Label.
^ 2.8L Federal
Manual Transmission
1. Advance base timing to a maximum of 2~ over specification if little or no detonation occurs at high altitude.
2. Reset-curb idle speed to 700 RPM in N (neutral).
3. Reset idle stop solenoid to 1100 RPM in N (neutral).
4. Reset fast idle speed to-, 2 300 RPM in N (neutral).
Automatic Transmission
1. Reset base timing to 12~ BTDC (before top dead center) if little or no detonation occurs at hiqh altitude.
2. Reset base idle speed to 700 RPM in D (drive).
3. Reset A/C solenoid speed to 850 RPM in D (drive).
4. Reset fast idle speed to 2100 RPM in N (neutral).
^ 4.3L Federal
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.OL/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.
PROCEDURE II
To be used for the following 1985 high altitude (NA6) engines used primarily at low altitudes.
FIGURE 3:
^ 1.9L Federal (refer to Figure 3).
1. Remove vacuum delay valve and rubber hose 'A' connected with white side of the delay valve from rubber hose 'B'.
2. Connect rubber hose 'B' directly with vacuum pipe where the rubber hose 'A' was connected.
^ 2.8L Federal
Manual Transmission
1. Retard base timing as much as 2~ from specification if detonation occurs at low altitude.
2. Reset curb idle speed to 700 RPM in N (neutral).
3. Reset idle stop solenoid to 1100 RPM in N (neutral).
4. Reset fast idle speed to 2300 RPM in N (neutral).
Automatic Transmission
1. Reset base timing to 12~ BTDC (before top dead center).
2. Reset curb idle speed to 700 RPM in D (drive).
3. Reset A/C solenoid speed to 850 RPM in D (drive).
4. Reset fast idle speed to 2100 RPM in N (neutral).
^ 4.3L Federal
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.OL/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 in D (drive).
4. Reset fast idle speed to specification on the Emission Control Information Label in N (neutral).
DEALERS AND CUSTOMER INFORMATION
Owners of the 1985 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.