Checking Fuel Pressure In Peugeot Jetronic Fuel Injection

Jetronic is a trade name for a manifold injection technology for automotive petrol engines, developed by Robert Bosch GmbH from the 1960s onwards. Bosch licensed the concept to many automobile manufacturers, including Peugeot.

There are several variations of the Jetronic technology, including D-Jetronic, K-Jetronic, KE-Jetronic, L-Jetronic, LE-Jetronic, LU-Jetronic, LH-Jetronic, and Mono-Jetronic. Each variation offers technological development and refinement.

The specific process for checking fuel pressure will depend on the type of Jetronic technology in use. For example, the process for checking fuel pressure in a K-Jetronic system will differ from that of a KE-Jetronic system.

It is important to consult the relevant manuals and seek professional guidance when checking fuel pressure in a Jetronic fuel injection system to ensure accurate measurements and avoid potential safety hazards.

How to test fuel flow from the pump

Before performing any diagnostic tests, it's important to prioritise safety. Releasing fuel under pressure can cause fires and injuries, so it is recommended to wear safety gear, such as safety glasses and gloves, and work in a well-ventilated area.

Step 1: Check the Fuel Pressure

Start by starting the car and letting it idle. Install a fuel pressure gauge and run the pump, noting the pressure reading. Compare this reading to the manufacturer's specifications. If the pressure is low, this issue should be addressed.

Step 2: Perform a Fuel Volume Test

If the fuel pump is supplying sufficient pressure, the next step is to determine if the proper amount of fuel is being delivered to the fuel injectors. This can be done by using a flowmeter or a glass measuring container.

Step 3: Collect a Fuel Sample

Start the car and let it idle. Collect a fuel sample for a specified duration, typically around five seconds, with the pump running. The pump should deliver a specific amount of fuel within this timeframe, which can be found in the manufacturer's specifications. You may need to convert the units to figure out the correct amount.

Step 4: Observe Fuel Pressure During the Test

It is important to ensure that the fuel pressure does not drop during the test. If the fuel pressure drops or if the collected fuel sample is less than the specified amount, it indicates insufficient volume.

Step 5: Block Off the Fuel System

If you observe insufficient volume, block off the fuel system and check again with the engine off. If adequate volume is achieved with the system blocked, it suggests a leakage in the system, such as a faulty fuel pressure regulator.

Step 6: Check for Restricted Filter or Line

If the volume remains low, it could be due to a restricted filter, line, or a faulty fuel pump. Replace the fuel filter and repeat the test, or use the proper adaptors to check the volume at the filter inlet.

Step 7: Test Fuel Pressure Without the Engine Running

To test fuel pressure without the engine running, an alternative means of powering the fuel pump is required. A technician can use a wiring diagram to determine how to supply voltage without the engine running, or use relay bypass devices that fit in place of the standard relay.

Step 8: Check Voltage and Amperage

Before condemning a fuel pump with low volume, check the voltage and amperage available to the pump. Check the voltage by back-probing the fuel pump connector. Lower voltage will cause the fuel pump to run slower and produce less pressure. Check fuel pump amperage with an ammeter in series with the power supply, typically at the fuel pump relay socket.

Step 9: Understand Residual Pressure and Hard Starting

To prevent hard starting, a check valve in the fuel pump closes to keep fuel in the lines. When the ignition is turned on, the fuel pump can quickly raise the pressure, and the engine starts. A leading cause of hard starting is fuel pressure that bleeds down too quickly. Residual pressure should remain in the system after turning off the ignition.

Step 10: Test Residual Pressure

Start the vehicle and note the fuel pressure as in the idle pressure test. Turning off the ignition should cause the fuel pressure to drop slightly, but it should not return to zero. A quick drop in fuel pressure indicates a leak in the residual pressure system, which could be due to leaking injectors, a faulty fuel pressure regulator, or a faulty fuel pump.

Step 11: Isolate Components

Use on/off adapters to isolate components and check for leaks. First, close the valve between the gauge and the fuel rail inlet, then turn on the ignition to build pressure and turn it off again. If the fuel pressure continues to drop, it indicates a leaking check valve in the fuel pump.

Step 12: Check the Injectors

To check the injectors for bleed-down, close the valve to the fuel line and open the valve to the fuel rail.

By thoroughly testing fuel pressure and volume, you can identify and resolve many issues related to fuel injection systems.

How to test system and control pressures

To test the system and control pressures, you will need a K-Jetronic-specific pressure tester. Using a generic fuel pressure gauge will not work. You can either obtain a good-quality tester or take your car to someone who has one.

Once you have the right equipment, follow these steps:

• Disconnect the fuel return line from the main regulator at the fuel distributor.
• Extend the return line by about 700mm and direct it into a suitable container of 1 litre or larger.
• Run the fuel pump for exactly 30 seconds and measure the amount of fuel in the container. You should have at least 750ml. A lower reading could indicate a restriction in the system (e.g. a blocked fuel filter) or a failing fuel pump.
• If the fuel flow is OK, reconnect the return line.
• Connect the pressure tester between the fuel distributor and the Warm-Up Regulator (WUR). The shut-off valve must be on the side of the gauge that connects to the WUR.
• Disconnect the electrical connector from the WUR to prevent it from heating up and changing pressures.
• With the shut-off valve open, you should be reading the Cold Control Pressure from the WUR. Control Pressure controls the enrichment of the fuel mixture.
• Check the correct Cold Control Pressure for your vehicle and ambient temperature from a manual. For example, at 20°C, the control pressure should be 0.6-0.9 bar.
• If the control pressure is within the correct range, you're good to go. If not, there could be a problem with the WUR or another component.
• Close the shut-off valve. You are now reading the System Pressure, which is the overall pressure the injection system is running at.
• Check the correct System Pressure for your vehicle from a manual. For example, the System Pressure should be about 5.1 bar. If it's not within the acceptable range, you may need to shim the regulator or replace the fuel pump.
• To test the Warm Control Pressure, either warm up the engine or leave the ignition and pump running with the electrical connector connected to the WUR. The heater in the WUR should warm up and allow you to test the warm pressure.
• Check the correct Warm Control Pressure for your vehicle and ambient temperature from a manual. For example, the Warm Control Pressure should be about 3 bar.
• The final test for the gauge is to check the accumulator and injectors for leaks. With the fuel pump running and the test gauge shut-off valve open, turn off the fuel pump and check the pressure after 10 and 20 minutes. If the pressure drops more than it should, run the pump again, shut it off, and shut the test gauge shut-off valve. If the pressure still drops, this indicates a leak in the accumulator.
• If the pressures are all within the correct range, there are a few other tests you can run to check the system, but they require disassembly and should be a last resort.

Other Tests

If you are still experiencing issues with the injection system, there are some additional tests you can perform:

• Test the accumulator, which is commonly located down by the fuel pump. Clamp the hose from the outlet of the accumulator, direct the vent hose into a container, and run the fuel pump. If the accumulator is OK, no fuel should come out of the vent.
• Test the fuel distributor. With the engine off and fuel pump on, raise the sensor plate by hand, drop it, and then quickly bring it back up again. If you can feel the plunger high up in the bore, it is sticking.
• Test the Cold Start Injector. Remove the injector from the manifold, direct its nozzle into a container, and connect the power connector from the Auxiliary Air Device (AAD) to the Cold Start Injector. Turn on the ignition and run the fuel pump. This should cause the injector to open and spray fuel. Disconnect the power, wipe the nozzle dry, and hold the injector in the container for 60 seconds to check for leaking.
• Test the Thermotime Switch by checking the resistance and continuity between the circuits when cold and when warm. When cold, Terminal A should have lower resistance than when warm. When warm, Terminal A should have higher resistance. When cold, Terminal D should have continuity with the body of the sensor with no resistance. When warm, Terminal D should show as an open circuit.
• Test the AAD by checking if you can see through the unit when cold and if it shows a solid plate when warm. You can also pinch off the hose on either side of the unit when the engine is at operating temperature. If the idle speed drops, the AAD is not closing properly.
• Test the electrical side of the WUR by checking for power at the plug and the resistance of the heater coil.
• Test the injectors for leaking and erratic spray patterns. Remove the injectors from the manifold, place them into containers, turn on the fuel pump, and lift the Air Sensor Plate to trigger the injectors. Check the flow pattern and measure the amount of fuel from each injector. If they are leaking, have an erratic spray pattern, or there is a variation in flow, the injectors need to be replaced.

How to test the accumulator and leaking injectors

To test the accumulator and check for leaking injectors, you will need to perform the following steps:

• With the fuel pump running, open the test gauge shut-off valve.
• Turn off the fuel pump and observe the gauge. The accumulator pressure should be at 2.5BAR.
• After 10 minutes, the pressure should still read 2.5BAR.
• After 20 minutes, the pressure should drop to 2.0BAR.
• If the pressure drops more than it should, run the pump again to build pressure, then shut off the pump and close the test gauge shut-off valve.
• If the pressure still drops, this indicates a leak before the gauge and is likely due to the accumulator.
• To test the accumulator further, clamp the hose from the outlet of the accumulator (usually the one that goes to the fuel filter).
• Remove the vent hose and direct a hose from the vent into a container.
• Run the fuel pump. If the accumulator is functioning correctly, no fuel should come out of the vent. If fuel comes out of the vent, the accumulator has failed.

Please note that this answer is based on general instructions for testing the accumulator and injectors and may not be specific to Peugeot Jetronic fuel injection systems. Always refer to your vehicle's owner's manual for specific instructions and safety precautions.

How to test the accumulator

To test the fuel accumulator, you can perform a fuel pressure test. This will indicate whether the accumulator is faulty or functioning well. The accumulator is usually associated with warm or hot starts, rather than cold starts.

Step 1: Understand the Function of the Accumulator

The accumulator maintains the pressure in the fuel system for a certain period after the engine has been switched off. When the engine is running, the accumulator also serves to muffle the noise of the electric fuel pump.

Step 2: Prepare the Necessary Tools and Safety Measures

Before beginning the test, ensure you have the required tools, such as a fuel pressure gauge and hoses. It is also important to take safety precautions, such as wearing protective gear and ensuring proper ventilation.

Step 3: Perform the Fuel Pressure Test

• Connect the fuel pressure gauge and hoses to the appropriate ports on the fuel distributor.
• Start the engine and observe the fuel pressure readings on the gauge.
• Take note of the control pressure and working pressure values.
• The control pressure is the pressure modified by the Electro-Hydraulic Actuator (EHA) and is usually lower than the working pressure.
• The working pressure is the raw pressure from the fuel pump.
• The difference between the control pressure and working pressure should be within a specified range (for example, 0.4 bar). If the difference is lower, it indicates a lean condition.

Step 4: Analyze the Results

If the fuel system is holding pressure after shutdown, the accumulator, check valve, and injectors are likely in good condition. If the system does not hold pressure, there may be an issue with the pump check valve, accumulator, or one or more injectors.

Additionally, you can perform a visual inspection of the accumulator. Disconnect the hose from the accumulator's spring chamber and observe the nozzle. If there is a steady fuel leak or drips, it indicates that the accumulator diaphragm has a pinhole leak, which can cause depressurization of the system over time.

How to test the fuel distributor

To test the fuel distributor, you will need to gain access to the component by removing any necessary parts that may be obstructing your view or preventing you from reaching it. This may involve removing the air cleaner assembly or other components. Once you have located the fuel distributor, which is typically found near the engine's cylinder head, you can begin the testing process.

• Understanding the Fuel Distributor and Its Components: The fuel distributor is responsible for dividing the single fuel supply line from the tank into smaller lines for each injector. It plays a crucial role in the fuel injection system by varying the fuel volume supplied to the injectors based on the angle of a moving vane in the airflow meter and the control pressure.
• Visual Inspection: Begin by visually inspecting the fuel distributor for any signs of damage, leaks, or corrosion. Pay close attention to the connections and hoses attached to the distributor. Look for any signs of fuel leaks or damage to the components.
• Testing Fuel Pressure: To test the fuel pressure, you will need a fuel pressure gauge. Connect the gauge to the appropriate ports on the fuel distributor. Start the engine and take fuel pressure readings. Compare these readings with the specified ranges to identify potential issues. The goal is to achieve a working pressure of 0.4 bar higher than the control pressure.
• Adjusting the Electro-Hydraulic Actuator (EHA): If the working pressure and control pressure differ significantly, you may need to adjust the EHA. Disconnect the electrical connector on the left side of the fuel distributor. Remove the EHA and adjust it using a 2mm Allen wrench. Reinstall the EHA and take fuel pressure readings again.
• Testing Individual Components: The fuel distributor consists of multiple components, such as the control pressure regulator (CPR) or the warm-up regulator (WUR). If you suspect an issue with a specific component, refer to manufacturer guidelines or seek professional assistance for testing and troubleshooting that particular part.
• Maintenance and Cleaning: Regular maintenance and cleaning of the fuel distributor are essential. Ensure that all connections are secure and free from corrosion. Keep the area around the distributor clean and tighten the mounting bolts periodically. Consider using injector cleaner solutions to prevent and address fuel-related issues.

It is important to note that working on fuel systems can be complex and potentially dangerous. If you are unsure or uncomfortable with any part of the process, it is always best to seek the help of a qualified mechanic or automotive technician. They can provide accurate diagnostics and perform any necessary repairs or replacements.

Frequently asked questions