This document provides a comprehensive guide for the replacement of the Stanadyne DS4 electronic injection pump commonly used in 1994 and later 6.5L diesel engines. The process requires careful attention to detail and the use of specialized tools to ensure proper installation and functionality.

The Stanadyne DS4 electronic injection pump is a critical component in the 6.5L diesel engine, and its replacement can be complex. This guide outlines the necessary steps to successfully remove and install the pump, ensuring that all components are handled correctly to avoid damage and ensure optimal performance.

• Identify the Pump: Before ordering a replacement, confirm the correct part number. The 1994 model year had two potential pump variations, so always check the ID tag on the pump.

• Relocate the PMD: Many 6.5L owners choose to relocate the Pump Mounted Driver (PMD) from the side of the injection pump to a cooler location. If you have not done this yet, now is an ideal time. New pumps are often sold without a PMD, assuming you will install one remotely.

• Gather Tools: You will need standard metric and imperial socket sets, extensions, wrenches (including an S-shaped wrench for hard-to-reach nuts), flare nut wrenches for fuel lines, and a torque wrench.

• Disconnect the Battery: Always disconnect both negative battery cables before beginning the replacement process.

Clean the engine valley to prevent debris from entering the engine. Drain and collect the fuel in a clean container.

• Remove the intake horn and air intake tube.

• Remove the intake manifold.

• Remove the oil fill neck.

• Using flare nut wrenches, loosen and disconnect the fuel injector lines at the pump and the injectors. Loosening them at both ends provides more flexibility for removal.

• Cover the open injector ports to prevent debris from entering the engine.

• Disconnect the main fuel feed and return lines from the pump.

Carefully remove all electrical connections from the pump, including the PMD harness.

Disconnect or remove other accessories as needed for access. For example, removing the AC compressor can make the process easier on 1996 and later vehicles.

The pump is held in place by three nuts and three bolts. Remove the injection pump drive gear bolts through the oil fill tube grommet. It is recommended to leave one top bolt and one nut until last to prevent the pump gear from skipping a tooth. However, some technicians prefer to remove the bolts from the pump gear first, followed by the nuts that secure the injection pump.

Mark the pump's position relative to the timing housing. This reference mark will assist in setting the new pump close to the correct timing. Remove the remaining nuts, then slide the injection pump rearward and lift it straight out of the engine valley.

• Replace the gasket on the flange where the pump mounts to the timing housing.

• Transfer the PMD to its new, relocated heat sink if you are using a new, non-pump mounted PMD.

The first step is to rotate the new injection pump shaft so the dowel is in the same orientation as the pump you removed. Slide the new pump into the timing housing, ensuring the dowel goes through the pump gear, and start one bolt through the gear to prevent the pump/gear from jumping a tooth. Align the new injection pump with the reference marks you made on the timing housing.

Tighten the bolts on the pump drive gear to 20-25 ft-lbs, using a small amount of Loctite on these bolts. Gently snug the injection pump nuts tight enough to be secure but loose enough to allow slight pump adjustments.

• Reinstall the oil filler tube.

• Reattach all fuel lines, using new injector return hoses and tightening fittings securely.

• Reconnect all electrical connectors.

Reinstall the intake manifold, heat shield, and air intake components.

The lift pump on some models only runs when the engine is cranking. On later models, or those running our upgraded lift pump harness, the lift pump will activate with the key. A manual hand pump can also be used to push fuel to the injection pump. Ensure that all air is removed from the system before attempting to start the engine.

Start the engine and allow it to run briefly. A final timing adjustment is required using a scan tool (such as a Tech 2). The tool reads the TDCO (Timing Desired Crankshaft Offset) and guides you in making fine adjustments by loosening the pump nuts and rotating the pump slightly.

Finally, re-check for leaks and ensure all components are properly secured.

For an in-depth look at the proper timing set and TDCO offset procedure, please refer to the articles on that subject.