Diesel Injection Pump O-Ring Replacement

A leaking diesel injection pump can be a frustrating and messy problem. Fuel seeping from the pump body often indicates that the rubber O-rings, responsible for sealing various components, have degraded over time due to age and exposure to diesel fuel. These O-rings become brittle and lose their elasticity, failing to create a watertight seal. This guide will walk you through the process of re-sealing your leaking in-line Zexel/Bosch PFR diesel injection pump, a common issue found in many tractors and other diesel-powered machinery. By following these steps, you can effectively stop fuel leaks and restore your pump to leak-free operation.

Understanding the Problem: Degraded O-Rings

The PFR style Bosch/Zexel injection pump is a robust unit, but like all rubber components, its seals are subject to wear and tear. The O-rings located on the pump bushings and their caps are particularly susceptible to degradation. When these seals fail, fuel can escape, leading to a noticeable mess around the pump and engine block. This leakage not only looks untidy but can also lead to a loss of fuel pressure and, in severe cases, contamination of engine oil if the fuel bypasses other seals.

Tools and Parts You'll Need

Before you begin, ensure you have the necessary tools and replacement parts. Using the correct, high-quality parts is crucial for a successful repair. Generic O-rings may not have the precise dimensions required, potentially leading to further issues, as one user discovered (see footnote 1).

Essential Tools:

• Dremel tool with a cutting disc
• Punch and hammer
• Metric sockets and open-end wrenches
• Needle-nose pliers

Replacement Parts (for a 4-cylinder engine):

You will need to source these parts from your tractor dealer or a reputable diesel parts supplier. Using the specific part numbers for your pump can ensure you get the correct items.

• 8 x O-rings for each pump bushing (2 per bushing)
• 4 x O-rings for each pump bushing cap (1 per cap)
• 4 x Copper washers for the spring in the cap
• 2 x Copper washers for the Banjo fitting
• 8 x New metric cap screws with washers for each pump bushing (hex head, hex-metric-flanged-cap-screw type recommended)

Tip: Diesel specialists often supply these parts at a lower cost than tractor dealerships. Look for Zexel or Bosch part numbers starting with '10413' (Zexel) or '9' followed by a 10-digit number (Bosch).

Step-by-Step Replacement Procedure

This procedure is designed for the Zexel/Bosch PFR inline injection pump and should take approximately 2-5 hours, depending on your experience level.

1. Shut off Fuel Supply: Turn off the fuel valve to the injection pump and disconnect the fuel line.
2. Remove Hard Lines: Carefully disconnect the steel fuel lines running from the injection pump to the injectors. Use two wrenches simultaneously on the fittings to prevent twisting the injectors or pump components.
3. Remove Solenoid: Detach the solenoid valve located on the side of the injection pump.
4. Unbolt the Pump: Remove the nuts and bolts securing the injection pump to the engine block.
5. Partially Remove Pump: Gently lift the injection pump about halfway out of the engine block. Using needle-nose pliers, remove the retaining clip that holds the pump's control rack bracket. Once the clip is removed, you can lift the injection pump completely clear of the engine block. Crucially, leave the shims (thin metal gaskets) that were between the engine block and the pump body in place or securely stored. These shims are vital for setting the pump's timing and should not be treated as simple gaskets.
6. Mark Flange Positions: This is a critical step for reassembly. Using your Dremel tool with a cutting disc, carefully create a permanent mark (a scratch or a small notch) on the outer edge of each pump flange relative to the pump body. This will ensure you reassemble the pump with the flanges in their original orientation.

Disassembling and Re-sealing the Pump Flanges

Now, you will work on the individual pump flanges, which house the fuel pumping elements.

7. Remove Flange Capscrews: Starting at one end of the pump, use the Dremel with a cutting disc to carefully cut a small notch into the outer edge of the 5-sided flanged cap screws that secure each pump flange. Insert a chisel into this notch and strike it with a hammer in a counter-clockwise direction to loosen and remove the cap screw. Repeat this for the second cap screw on that flange. Once both cap screws are removed, you can carefully remove the pump flange-bushing assembly (the unit with two O-rings on the outside that holds the small internal plungers).
8. Address Bushing Components: With the pump flange-bushings removed from the main pump body, be mindful not to turn the pump body upside down, as the internal gear or control sleeve could dislodge and require re-alignment (see footnote 2). For each flange-bushing, remove the top hex fitting (the cap). Here's what to do with each component:
   • a) Replace the O-ring located on the cap, just above the threads.
   • b) Replace the copper washer situated inside the cap, beneath the spring.
   • c) Reinstall the hex cap onto the pump bushing and finger-tighten it for now.
9. Replace Bushing O-Rings: On each pump flange-bushing, carefully remove the two old O-rings from the grooves on the bushing body. Lightly lubricate the new O-rings with a suitable lubricant (diesel fuel or a light oil can work) and slide them into their respective grooves. Gently but firmly insert the pump flange-bushing back into its corresponding hole in the pump body. A light coating of lubricant on the O-rings will aid in seating them correctly. Ensure your alignment marks from Step 6 are perfectly matched. Insert the new metric cap screws into the pump body and torque them down to secure the flange-bushing in its proper position.
10. Tighten Flange Caps: Tighten the hex cap on each pump flange-bushing to the manufacturer's specified torque setting. Double-check that your alignment marks (from Step 6) still match perfectly.
11. Repeat for All Flanges: Repeat Steps 8 through 10 for each remaining pump flange-bushing on the injection pump.

Testing and Reinstallation

Once all the O-rings have been replaced and the flanges are reassembled, it's time to test the pump and reinstall it.

12. Test the Pump: To test the pump's functionality, remove the banjo fitting. Fill the pump with mineral oil (baby oil is a good, non-toxic alternative). Hold the filled pump securely in both hands. Gently but firmly press the pump base roller against a small block of wood or a similar firm surface. You may need to apply sufficient force to get the nozzle to squirt a small drop of oil. Repeat this process for each nozzle to ensure they are all priming and discharging. A strong, consistent squirt from each nozzle indicates the pump is likely working correctly.
13. Replace Banjo Fitting: Reinstall the banjo fitting, making sure to use the two new copper washers.
14. Reinstall Injection Pump: Carefully guide the injection pump body back into the engine block. Align the hole in the bracket arm with the stub of the control rack and meticulously replace the retaining clip (be careful not to drop it!). Once the clip is in place, push the pump fully into the engine block and torque down the securing bolts to the correct specification.
15. Reconnect Fuel Line: Reattach the main fuel line to the banjo fitting on the rear of the injection pump. Leave the air bleeding screw (located on top of the banjo fitting) open a few turns.
16. Reconnect Hard Lines: Reinstall the steel fuel lines between the injection pump and the injectors. Again, use two wrenches on fittings to prevent twisting. Leave one steel injector line connection slightly loose at the fuel injector. This will allow air to bleed out of the system as you start the engine.
17. Bleed Air and Start: Turn on the fuel supply valve. Once fuel begins to seep from the loose banjo fitting, close the screw. Now, crank the engine. Continue cranking until fuel emerges from the deliberately loosened fitting at the fuel injector. Once fuel is seen, tighten the final hard line connection at the injector. The engine should now start.
18. Dispose of Old Parts: Properly dispose of the old, 5-sided cap screws.

Footnotes

Footnote 1: Importance of Correct O-Ring Size

An early attempt at this repair using O-rings that were close in size but not exact resulted in failure. The incorrect O-rings, particularly the lower one on the pump bushing, moved out of its groove and tore during installation. This led to the tractor not starting and a significant amount of diesel fuel leaking into the engine crankcase, causing a messy overflow from the dipstick tube. The use of correctly sized OEM O-rings resolved the issue, highlighting the critical need for precise dimensions.

Footnote 2: Re-aligning Control Sleeves

While it's possible to remove and re-insert the geared control sleeves, it's essential they are realigned correctly. Although there are tiny alignment marks on the gear and control rack, it's often easier to visually align the tops of the plungers so they match the orientation of the other three plungers. This ensures all plungers rotate in unison with the movement of the control rack.

Frequently Asked Questions

Q1: Why is my diesel injection pump leaking fuel?

A1: The most common reason for a diesel injection pump to leak fuel is that the rubber O-rings and seals within the pump have become old, brittle, and have lost their elasticity. This prevents them from creating a proper seal, allowing fuel to escape.

Q2: Can I use any O-rings to replace the ones in my injection pump?

A2: No, it is highly recommended to use O-rings that are specifically designed for your injection pump model. The dimensions and material of these O-rings are critical for a proper seal. Using generic or incorrectly sized O-rings can lead to leaks, improper pump operation, or even damage.

Q3: How long should this repair take?

A3: The time required for this repair can vary depending on your experience level. Generally, it can take between 2 to 5 hours to complete the replacement of the O-rings on a Zexel/Bosch PFR injection pump.

Q4: What is the purpose of the shims between the engine block and the injection pump?

A4: The shims are not just gaskets; they are crucial for setting the precise timing of the injection pump. They must be kept in their original position and orientation during the pump's removal and reinstallation to ensure correct engine timing.

Q5: What should I do if the control sleeve or gear inside the pump comes loose?

A5: If the internal gear or control sleeve becomes dislodged, it needs to be re-aligned correctly. While there may be small alignment marks, a practical method is to visually align the tops of the plungers to match the position of the other plungers, ensuring they rotate in unison.

Q6: Is it possible to re-seal other types of injection pumps, like a Bosch VE unit?

A6: Yes, many types of diesel injection pumps, including the Bosch VE unit found in vehicles like Peugeots, can be re-sealed. While the specific procedure might differ, the general principle of replacing degraded seals remains the same. Information and guides for servicing various pump types are often available online or from manufacturer resources.