Procedure I

To be used for the following carbureted 1987 and 1988 low altitude (NA5) H.D. engines used primarily at high altitudes.

^ 5.7L (LT9)

1. Advance base timing to a maximum of 4 degrees over specifications if little or no detonation occurs at high altitude.

2a. Manual Transmission

Do not adjust the carburetor vacuum break.

2b. Automatic Transmission

Set carburetor vacuum break to 26 degrees.

3. Set base, A/C solenoid (if present) and fast idles to the specifications on Emission Control Information Label (P/N 10123811).


^ Heavy Duty Gasoline Emission Packages 4.8L (L25) and 7.4L (LE8)

(Carbureted Models Only)


1. Advance base timing to a maximum of 4 degrees over specification if little or no detonation occurs at high altitude.

2. Set idle speed to specifications per Emission Control Information Label (P/N 10123811).


^ Federal 6.2L Diesel Engine (LL4 and 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 Bulletin detailing the timing procedure to follow.


4. Install Emission Control Information Label (P/N 10123811).


DEALERS AND CUSTOMER INFORMATION FOR HIGH TO LOW ALTITUDE OPERATION

Owners of 1987 and 1988 high altitude vehicles taking up permanent residence in a low altitude county, should be encouraged to have their vehicle adjusted when 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 ADJUSTED TO LOW ALTITUDE SPECIFICATIONS PER THE CORRECT CHASSIS SERVICE MANUAL, FOR IMPROVED PERFORMANCE. IF ADJUSTED TO LOW ALTITUDE SPECIFICATIONS, THE SUPPLEMENTAL LABEL SHOULD BE REMOVED.