6.2 and 6.5L Handbook
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Setting DS4 Injection Pump TimingOverviewRequired ToolsProcedureStep 1: Initial Timing PositionStep 2: TDCO LearnStep 3: Fine AdjustmentStep 4: Final SecuringTroubleshootingTechnical Notes
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Timing an EFI 6.5L with the GM TECHII

Edited

Setting DS4 Injection Pump Timing

Overview

This guide provides step-by-step instructions for setting the timing on a DS4 injection pump using a scan tool with TIME SET and TDCO Learn capabilities.

Required Tools

  • Scan tool (TECH II recommended)

  • Basic hand tools for pump adjustment

Procedure

Step 1: Initial Timing Position

  1. Access the "Time Set" feature on your scan tool

  2. Adjust the pump position until the "Actual Timing" reading averages approximately 3.5

    1. With TIME SET set to ON, the stepper motor moves to 0* DESIRED TIMING advance and ACTUAL TIMING reads back a number. This number is the degrees the injection pump is advanced in relation to the crankshaft at top dead center.

      • Note: Some slight fluctuation in the reading is normal. It will not be perfectly steady

      • Note 2: The definition of what the "ACTUAL TIMING" number is showing you changes when you activate the TIME SET feature ON. What "ACTUAL TIMING" says at a normal idle (8-14*) has NOTHING to do with what the number means during this procedure. This is probably the #1 most confusing part of how GM implemented this process.

Important Note for Advanced Users: While experienced technicians may skip the TIME SET command, novice users should always perform this step to ensure accurate positioning.

Step 2: TDCO Learn

  1. Perform a "TDCO Learn" procedure

  2. Record the resulting TDCO (Top Dead Center Offset) value

Step 3: Fine Adjustment

  1. Make small incremental adjustments to the pump position

  2. Perform TDCO Learn after each adjustment

  3. Continue adjusting until reaching desired specifications:

    • Factory setting: -0.50

    • Acceptable range: -0.25 to -0.75

Step 4: Final Securing

  1. Verify final TDCO value is within specification

  2. Tighten all three pump retaining nuts to proper torque specification

Troubleshooting

If TDCO Learn returns the following values:

  • OBDI: -1.94/+1.94

  • OBDII: -2.46/+2.46

These readings indicate either:

  1. The pump position needs to be reset using the Time Set feature (return to Step 1)

  2. A potential mechanical issue exists that requires investigation

Technical Notes

  • A TECH II scan tool is strongly recommended for this procedure

  • Not all scan tools support the TIME SET function, which may complicate the timing process

  • The TIME SET feature significantly reduces the time required for accurate pump positioning

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