Engine - High Altitude Conversion and Adjustment
No.P-4243
25-05-88
Date
October 10, 1988
Index
EMISSIONS
Subject
High Altitude Conversions and Adjustments for Improved Engine Performance at Altitude (4000 Feet and Above)
Models
1988 B-D-N-W-AD- & AW-Trucks
Instructions are now available to accommodate a customer who may wish to convert a 1988 low-altitude vehicle for improved high-altitude engine performance.
Vehicles with the low-altitude package transferred to service in high-altitude areas may exhibit undesirable driveability. However, the installation of a high-altitude conversion is voluntary and at the customer's expense.
The high-altitude field conversion packages and procedures outlined below have been authorized on the following 1988 nonaltitude-equipped engine families in service at altitudes 4,000 feet above sea level.
CONVERSION INSTRUCTIONS
Sea Level to Altitude
IMPORTANT:
IN ALL OF THE CONVERSION PROCEDURES YOU WILL BE REQUIRED TO INSTALL A NEW VEHICLE EMISSION CONTROL INFORMATION UPDATE LABEL, PN 4375084.
THIS LABEL HAS TWO AREAS THAT ARE IMPACT IMPRINTABLE WITH A TYPEWRITER (SEE FIGURE 1.)
If you are required to readjust timing, curb idle speed, or fast idle speed to a specification different than the original VECI label specification, type in the new specification. If you are asked to refer to the original VECI label specifications, type in on the right hand side of the label "refer to original VECI label."
Type in Technical Service Bulletin 25-05-88 and your dealer code as shown in Figure 1. Label, PN 4275084, is available from the parts supply.
The following chart should be used to identify what parts must be used on what package.
Engine and Body Application Parts Required
2.2L - 2V Federal & California N-Body 4275084 Label
5.9L - 4V Federal & California B- & D-Body 4306424 Carburetor
4275084 Label
On 1988 N-body trucks equipped with 2.2L - 2V engines, Federal and California emissions, readjust idle mixture at altitude.
On 1988 B-* & D-Bodies Do the Following:
1. Remove original carburetor and install new carburetor, PN 4306424, as outlined in the service manual.
2. As outlined in the service manual, adjust idle specifications as follows:
Manual Automatic
Idle RPM 750 750
Propane RPM 780 780
MSIS RPM 750 850
Timing RPM 750 +0, -150 710 +0, -150
3. Type "This vehicle has been modified to meet altitude emissions standards" on the VECI update label, PN 4275084, and affix near VECI label.
* B-vans less than 8500 GVW
On 1988 B300 Models Greater Than 8500 GVW:
1. Remove original carburetor and install new carburetor, PN 4306424, as outlined in the service manual.
2. As outlined in the service manual, adjust idle and choke specifications as follows:
Manual or Automatic
Idle RPM 750
Propane RPM 780
MSIS RPM 850
Timing RPM 710 +0, -150
Choke Kick 27 Degrees
3. Type "This vehicle has been modified to meet altitude emissions standard" on the VECI update label, PN 4275084, and affix near VECI label.
POLICY:
Information only