Replacing the injection pump on a TDI ALH engine is a task that requires precision and a good understanding of diesel engines. This guide provides a detailed, step-by-step walkthrough for replacing your Tdi Alh Injection Pump, ensuring optimal performance and longevity for your vehicle. Whether you’re a seasoned mechanic or a dedicated DIYer, this guide will equip you with the knowledge to tackle this important maintenance procedure.
Before beginning, it’s crucial to understand the significance of the injection pump in your TDI ALH engine. The injection pump is responsible for delivering fuel to the injectors at precisely the right time and pressure, which is critical for efficient combustion and engine performance. A faulty injection pump can lead to a range of issues, from poor fuel economy and reduced power to engine misfires and no-starts.
This guide builds upon existing knowledge and aims to be a comprehensive resource, ensuring a smooth and successful injection pump replacement. Let’s get started.
Step-by-Step Injection Pump Replacement
1. Preparation and Safety Precautions
Before you begin, ensure your vehicle is safely supported, preferably on jack stands. Disconnect the negative battery terminal to prevent any electrical mishaps during the process. Gather all necessary tools and materials, which we’ll detail in the next section. Safety is paramount, so wear appropriate safety glasses and gloves throughout the procedure.
2. Tools and Materials Needed
Having the right tools will make this job significantly easier and safer. Here’s a list of essential tools and materials you’ll need:
- New TDI ALH Injection Pump
- New Copper Washers (for fuel line connections)
- Timing Belt Kit (consider replacing if due or unknown age)
- Universal Sprocket Buster™ Counter-Hold Tool (or equivalent)
- Universal Cam Locking Plate (or equivalent TDC locking tools)
- A4 TDI Pump Pin (or injection pump locking pin)
- Compact 3-way Tensioner Wrench (or similar belt tensioner tool)
- Socket Set (including 10mm, 13mm, 17mm, 19mm sockets, deep sockets recommended)
- Wrench Set (including 13mm, 17mm open-end and box-end wrenches)
- Allen Wrench Set (including 5mm Allen socket)
- Torque Wrench (capable of measuring 7 ft-lb, 15 ft-lb, 18 ft-lb, 33 ft-lb, and 40 ft-lb ranges)
- Mirror and Light (for inspection in tight spaces)
- Hand Operated Vacuum Pump (e.g., Mityvac Model 04000)
- Shop Towels
- Coolant (if thermostat replacement is also performed)
- Brake Cleaner
- Pen or Marker (for marking fuel lines)
3. Step-by-Step Installation Process
a. Initial Setup and TDC (Top Dead Center)
Begin by ensuring your engine is at Top Dead Center (TDC) for cylinder number 1. This is crucial for correct timing.
- Rotate the engine manually until the camshaft lobes for cylinder number 1 are pointing upwards.
- Verify the brake booster vacuum pump groove at the end of the camshaft is horizontal.
- Install the Universal Cam Locking Plate to secure the camshaft in the TDC position. This ensures that the camshaft timing remains accurate during the injection pump replacement.
b. Timing Belt Tensioner and Routing Inspection
Before proceeding, inspect the timing belt routing and tensioner.
- Use a mirror and light to check that the tensioning roller retaining tab (upper left) is correctly seated in the hole in the timing belt guard. This small detail is important for proper tensioner function.
Alt text: Close-up view showing the tensioning roller retaining tab correctly seated in the timing belt guard hole, essential for proper timing belt tension.
- Refer to a diagram or photo to ensure the timing belt is correctly routed around all pulleys and rollers. Correct routing is vital for engine timing.
Alt text: Diagram illustrating the correct routing of the timing belt around the crankshaft pulley, camshaft pulley, injection pump pulley, and tensioner roller in a TDI ALH engine.
c. Injection Pump Sprocket Bolt – Temporary Tightening
Now, focus on the injection pump sprocket.
- Temporarily tighten one of the injection pump sprocket bolts modestly. Place the bolt in the middle of the elongated hole of the sprocket to allow for fine adjustments later. Do not fully torque it at this stage, as it will need to be loosened again for final timing adjustments.
d. Camshaft Sprocket Bolt – Reinstallation
Secure the camshaft sprocket.
- Using the Universal Sprocket Buster™ Counter-Hold Tool to hold the camshaft pulley stationary, reinstall the camshaft sprocket bolt by hand. Do not torque it fully yet.
e. Injection Pump Pin and TDC Re-Verification
Ensure timing accuracy is maintained.
- Loosen the injection pump sprocket bolt you previously tightened.
- Confirm the A4 TDI Pump Pin is still correctly inserted and centered in its elongated hole. This pin locks the injection pump at its correct timing position.
- Re-verify that the crankshaft is still at TDC. Double-check the camshaft lobes, vacuum pump groove, and ensure the Universal Cam Locking Plate is still in place. Precision at this stage prevents timing issues.
f. Timing Belt Tensioner Adjustment
Adjust the timing belt tension.
- Ensure the two holes on the tensioner are rotated to the bottom position.
- Verify the tensioning roller retaining lug remains seated in the hole on the timing belt guard.
- Hand-tighten the nut on the timing belt tensioner.
Alt text: Image showing the timing belt tensioner being adjusted with a specialized wrench, aligning the notch and raised mark for correct belt tension as per Bentley Manual.
g. Belt Tensioning with Tensioner Wrench
Proper belt tension is critical for engine longevity and performance.
- Using the Compact 3-way Tensioner Wrench in the center holes of the belt tensioner, tension the belt by turning clockwise.
- Adjust until the notch on the tensioner aligns with the raised mark. For automatic transmission vehicles, Bentley Manual advises using an Allen wrench on the belt tensioner.
- Tighten the tensioner lock nut to a “Good-and-Tight” feel using a 13mm boxed-end wrench, while maintaining the tensioner position with the Compact 3-way Tensioner Wrench. The limited space due to the engine mount bracket often makes a socket wrench impractical here. Marking the tensioner nut during removal (as recommended in the removal section) can be a helpful reference.
- Use a mirror to double-check that the notch and raised mark on the tensioner remain aligned after tightening.
h. Final TDC and Pump Pin Check
One last check before final torqueing.
- Ensure everything is still at TDC and that the A4 TDI Pump Pin remains securely in place.
i. Camshaft Sprocket Bolt – Final Torque
Now, torque the camshaft sprocket bolt to its final specification.
- Using the Universal Sprocket Buster™ Counter-Hold Tool to hold the camshaft pulley, torque the camshaft sprocket bolt to 33 ft-lb (45 Nm) using a 19mm socket. Some technicians recommend increasing the torque by about 20% to 40 ft-lb (54 Nm) for added security. Choose the torque value based on your comfort and experience, but ensure it is within a safe and recommended range.
j. Injection Pump Sprocket Bolts – Final Torque
Torque the injection pump sprocket bolts.
- Tighten the three bolts on the injection pump sprocket just enough to hold the sprocket in place initially using a 13mm socket.
- Then, torque these bolts to 18 ft-lb (25 Nm).
k. Remove Locking Tools
With all critical bolts torqued, remove the locking tools.
- Remove the Universal Cam Locking Plate.
- Remove the A4 TDI Pump Pin from the injection pump.
l. Manual Engine Rotation and Timing Verification
Manually rotate the engine to verify timing and ensure no interference.
- Using the Universal Sprocket Buster™ Counter-Hold Tool, rotate the camshaft CLOCKWISE for two complete rotations. Alternatively, you can rotate the engine using the crankshaft sprocket bolts.
- You should feel compression during the rotation, which should ease off if the timing is correctly set. If you encounter excessive resistance or hear valve noise, immediately stop and re-check all TDC settings and bolt torques.
- If the transmission was accidentally left in gear, ensure it is now in neutral.
- After two full rotations, cylinder Nr. 1 should return to TDC, with the cam lobes pointing upwards.
m. Reconnect Injection Pump Wiring
Reconnect the electrical components.
- Reconnect the harness connector for the injection pump wiring.
- Secure the connector back into its retaining bracket.
n. Reinstall Vacuum Pump and Valve Cover
Reassemble the vacuum pump and valve cover components.
- Reinstall the three bolts for the vacuum pump using a 13mm deep socket and/or 13mm offset box wrench, torquing them to 15 ft-lb (20 Nm). Remember to use a new vacuum pump seal if available or ensure the old one is in good condition.
- Reinstall the valve cover using a long 5mm Allen socket, torquing bolts to 7 ft-lb (10 Nm). If you removed the Oil By-Pass filter line from the valve cover, reconnect it now.
o. Reinstall Vacuum Line Support Bracket and Glow Plug Wires
Reattach vacuum lines and glow plug wires.
- Reinstall the vacuum line support bracket using a ¼-inch drive 10mm deep socket or 10mm offset box wrench underneath the vacuum pump, and then reconnect the vacuum line.
- Reinstall the three glow plug wires in front of the vacuum pump, ensuring they are correctly connected to their respective glow plugs.
p. Reinstall Timing Belt Guard and Intake Components
Reassemble the remaining engine components.
- Reinstall the upper timing belt guard, which is held in place by five clips. Ensure all clips are properly engaged.
- Reinstall the EGR valve or race pipe if it was removed during disassembly.
- Reinstall the upper intake pipe and hoses, connecting them to the EGR valve or race pipe and to the intercooler.
q. Reinstall Headlight and Bumper Cover
Reassemble the vehicle’s exterior components.
- Reinstall the passenger side headlight and the bumper cover in the reverse order of their disassembly.
r. Reconnect Fuel Lines to Injection Pump
Reconnect the fuel lines, ensuring correct order and tightness.
- Reinstall the fuel lines (2, 1, 4, 3) to the injection pump. Tighten them using a 17mm open-end wrench to the tightness marked at the beginning of the process. Ensure they are adequately tight to prevent leaks.
s. Install Fuel Supply Line
Connect the fuel supply line.
- Pull the rubber plug from the injection pump fuel supply inlet.
- Install the fuel supply line connector onto the top of the injection pump using a 17mm deep socket, torquing to 18 ft-lb (25 Nm). Use a new copper washer to ensure a leak-free seal.
t. Install Banjo Return Fuel Line
Connect the banjo return fuel line.
- Install the banjo return fuel line and cap nut onto the injection pump using a 17mm socket, torquing to 18 ft-lb (25 Nm). Use three new copper washers: one between the injection pump and the union, and one on each side of the banjo return fuel line to ensure proper sealing.
Alt text: Detailed view of the banjo return fuel line connected to the TDI ALH injection pump with new copper washers for sealing, highlighting the correct assembly order.
u. Reinstall Braided Return Fuel Line and Fuel Line Clips
Reattach remaining fuel lines and clips.
- Reinstall the braided return fuel line from Injector Nr. 4 to the injection pump, ensuring it is placed back onto the plastic clip attached to the vacuum reservoir bracket.
- Reinstall the two fuel line clips using a 10mm socket to secure the fuel lines in place.
v. Reinstall Vacuum Reservoir and CCV System
Reassemble vacuum and crankcase ventilation systems.
- Reinstall the vacuum reservoir ball and CCV (Crankcase Ventilation) system components.
w. Prime Fuel System
Priming the fuel system is crucial for starting after injection pump replacement.
- Reinstall the fuel supply line and remove its hose clamp.
- Prime the injection pump by drawing diesel fuel using a hand-operated vacuum pump. Initially, vacuum pressure may be low, but continue pumping. You will observe air bubbles in the clear fuel supply line, which will eventually disappear. Once the vacuum pump holds pressure, you should see a small amount of diesel fuel exiting the return line.
Alt text: Image demonstrating the process of priming the TDI ALH injection pump using a hand-operated vacuum pump connected to the fuel lines, showing air bubbles being removed from the fuel system.
x. Bleed Injectors (Injector Crack)
Bleed any air from the injector lines.
- Reinstall the fuel return line and remove its hose clamp.
- Crack loose the nut on top of Injector Nr. 3, wrap a shop towel around it to catch fuel spillage, and crank the engine for a few seconds until fuel emerges. Retighten the nut.
- Repeat this process for Injector Nr. 2. This step also helps to center the timing belt on the pulleys and allows the tensioner to remove any remaining slack.
Alt text: Image showing the process of bleeding air from a TDI injector by loosening the fuel line nut and allowing fuel to purge air, a necessary step after injection pump replacement.
y. Start Engine and Check for Leaks
Final steps: starting the engine and checking for leaks.
- Start the engine. It should start within a few seconds of cranking. The engine might initially cough or shudder slightly but should quickly settle into a smooth idle.
- If the engine fails to start even after priming, re-verify TDC settings and ensure no steps were missed during reassembly.
- Thoroughly check for fuel leaks around all fuel line connections and the injection pump itself. If the thermostat was also replaced, check for coolant leaks and ensure the coolant level is correct.
z. Final Reassembly
Complete the reassembly and final checks.
- Reinstall the skid plate or belly pan.
- Lower the car off of the jack stands.
- Re-check the coolant level if the thermostat was replaced.
Conclusion
Replacing the TDI ALH injection pump is a detailed but manageable task with the right tools and guidance. By meticulously following these steps and paying close attention to timing and torque specifications, you can successfully replace your injection pump and restore your TDI ALH engine to optimal running condition. Remember to double-check all connections for leaks and verify timing after the procedure to ensure a successful and reliable repair. If you are ever uncertain about any step, consulting a professional mechanic is always a prudent decision.
