Checking Fuel Pressure: Diy Guide For Your 560Sl

Checking the fuel pressure on a 560SL is a complex process that requires careful attention to safety. There are several ways to test fuel pressure, and it is important to use the correct tools and procedures to get accurate results. The fuel pressure regulator, for example, has been described as having two screw-on fittings for high pressure and one rubber outlet, which may be a vacuum port or a vent line. It is also important to ensure that the engine is warmed up before taking measurements, as a cold engine can affect the accuracy of the readings.

Check the fuel pressure regulator

Checking the fuel pressure regulator on a 560SL involves testing the fuel pressure and identifying any issues. Here's a step-by-step guide:

Step 1: Connect the Fuel Pressure Gauge

Obtain a suitable fuel pressure gauge and connect it to the correct port. This port is typically located near the fuel line or the fuel pump. Ensure you are connecting to the correct place as per the manufacturer's instructions.

Step 2: Turn on the Ignition

Once the gauge is connected, turn the ignition to the "on" position. Observe if there are any changes in the fuel pressure reading.

Step 3: Crank the Engine

Attempt to crank the engine and monitor the fuel pressure. Note that the pressure should gradually increase as you crank the engine. If the pressure rises slowly or does not reach the expected range, there may be an issue with the fuel system.

Step 4: Check the Fuel Pressure Reading

For a 560SL, the fuel pressure should ideally be within the range of 75-90 PSI. If the pressure is significantly below or above this range, it may indicate a problem with the fuel pressure regulator or other components.

Step 5: Perform Additional Tests (if needed)

If the fuel pressure is not within the desired range, you may need to perform further tests to pinpoint the issue. This can include jumping the pins on the fuel pump relay and checking the control pressure and system pressure separately.

Step 6: Inspect the Fuel Lines and Connections

Inspect the fuel lines and connections for any signs of leaks or damage. Leaking fuel lines or faulty connections can affect fuel pressure and regulator performance.

Step 7: Clean or Replace the Fuel Pressure Regulator

If the fuel pressure regulator is found to be faulty or clogged, it may need to be cleaned or replaced. This involves removing the regulator, cleaning or replacing the diaphragm, and ensuring all connections are secure.

It is important to refer to the specific instructions and guidelines provided by Mercedes-Benz or a qualified mechanic for your vehicle's make and model when performing these steps.

Check the fuel pump relay

To check the fuel pump relay on a 560SL, you will need to perform a fuel pump relay test. Here is a step-by-step guide on how to do this:

• Prepare the necessary materials: a 2.5 mm2 (12 AWG) electrical wire, two single pole plugs, and a Part No. 004 545 84 28. Ensure your battery is charged to at least 60% before beginning the test.
• Refer to the provided wiring diagram to familiarise yourself with the relevant components and their locations.
• Locate the fuel pump relay and remove it.
• Install a fused jumper wire from terminal #7 to #8 in the relay connector.
• Check if the fuel pump runs. If it doesn't, proceed to the next step.
• Inspect the positive cable on the battery for any loose wires. Power to the fuel pump relay comes from the battery and goes to the X4/10 connector, then on to the relay.
• If you are still experiencing issues, inspect your fuses. Ensure that the ground wire on the fuel pump is properly attached to the frame.

If you are bench-testing the fuel pump relay, you can refer to the attached documents provided in one source for the actual test and reference.

Check the cold start injector

To check the cold start injector on your 1987 560SL, you'll need to perform a few tests to diagnose the issue. Here's a step-by-step guide:

Step 1: Check Power to the Cold Start Injector

First, you need to determine if the cold start injector is receiving power. This can be done by checking the fuse and relay for the cold start system. In your case, the issue could be related to the overvoltage protection relay, which is mounted above the fuse box on the passenger side kick panel. Remove the panel below the passenger-side dash to access the relay. Check the fuse in the top of the relay and replace it if necessary. If the fuse is fine, try replacing the relay itself.

Step 2: Test Fuel Flow

If the power issue is resolved but the cold start injector still isn't working, the next step is to test the fuel flow. You'll need to connect a fuel pressure gauge to the correct port. For the cold start injector specifically, one user connected it to the cold start port. You can then turn the ignition on and observe the fuel pressure. If there's no change in pressure when turning the ignition on, it may indicate an issue with the fuel pump or a blockage in the fuel line.

Step 3: Check Fuel Pump and Fuel Lines

To further isolate the issue, you can test the fuel pump and fuel lines. Ensure that the fuel pump is operational by listening for it when the ignition is turned on. If the pump is running, but fuel isn't reaching the injectors, there could be a blockage in the fuel lines. Clear any blockages and ensure the fuel filter is clean.

Step 4: Inspect the Fuel Distributor

If the previous steps don't resolve the issue, the problem may lie with the fuel distributor. Check the return line on the distributor by jumping the relay and observing fuel flow. If there's good flow through the distributor but no fuel coming out to the lines, the distributor may be clogged and need to be replaced or cleaned.

Step 5: Seek Professional Help

If you're uncomfortable performing any of these steps or if the issue persists, it's recommended to consult a certified Mercedes-Benz technician or a mechanic who specializes in fuel injection systems. They will have the necessary tools and expertise to diagnose and resolve the issue.

Remember to refer to your owner's manual or seek guidance from a qualified professional for detailed instructions specific to your vehicle.

Check the fuel distributor

To check the fuel distributor on a 560SL, you will need to perform a series of tests to diagnose the issue. Here is a step-by-step guide:

Step 1: Check the Fuel Lines

• Disconnect all the fuel lines from the injectors and crank the engine.
• Observe if there is an initial burst of fuel, which indicates the cold start injector is functioning.
• If there is no fuel coming out after the initial burst, hold the starter for 20 seconds to give it time.

Step 2: Test the Fuel Distributor

• With the fuel lines disconnected, perform a test by pushing down on the air meter plate with the pumps running.
• Observe if fuel comes out of the top ports that connect to the injectors.
• If there is no fuel coming out, the fuel distributor may be clogged and needs further attention.

Step 3: Check Return Line on the Distributor

• Ensure fuel is flowing through the return line when the pumps are energised by jumping the relay.
• Take a line off the top of the distributor and observe if fuel comes out during cranking.
• If there is no consistent fuel flow, the fuel distributor may be clogged.

Step 4: Clean or Replace the Fuel Distributor

• Attempt to unclog the fuel distributor using compressed air at low pressure and a brake cleaner soak.
• If cleaning does not work, consider purchasing a rebuilt fuel distributor with a warranty.

Step 5: Reinstall the Fuel Distributor

• Mark and disconnect all fuel injector lines from the fuel distributor.
• Remove the clamp holding the fuel line connected to the Cold-Start Valve using a 10mm socket wrench.
• Disconnect the fuel line from the Cold-Start Valve with a 17mm open-end wrench.
• Disconnect the remaining fuel lines with a 17mm open-end wrench.
• Lift off the fuel distributor and inspect the fuel injection port for any signs of contamination or deposits.

Remember to take appropriate safety precautions when working on your vehicle, including wearing safety glasses and work gloves, and disposing of all fluids safely.

Check the fuel lines

To check the fuel lines of your 560SL, you will need to perform a fuel pressure test. This will involve using a fuel pressure gauge and connecting it to the correct place in the fuel system.

Firstly, locate the fuel pressure port. This is usually found near the fuel injectors or the fuel rail. Once you have located the port, connect the fuel pressure gauge to it. With the ignition turned to the "on" position, you should see the fuel pressure reading on the gauge. If the pressure is below or above the specified range, there may be an issue with the fuel lines or other components in the fuel system.

If you are not getting any reading on the gauge, there could be a blockage in the fuel lines or the fuel pump may not be functioning properly. In this case, you will need to check the fuel lines for any signs of damage or blockage.

To check the fuel lines for blockage, you can start by inspecting the lines for any visible damage, such as cracks, leaks, or kinks. If the lines appear to be damaged, they will need to be replaced. If the lines look intact, you can try using a fuel line pressure tester to check for any blockages. This tool will allow you to pressurize the fuel lines and check for any leaks or restrictions.

Another way to check for blockages in the fuel lines is to use a piece of wire or a small gauge to insert into the lines. If the wire encounters any resistance or blockage, it indicates that the line is clogged and needs to be cleaned or replaced.

If you suspect that the fuel pump may be the issue, you can test it by connecting the fuel pressure gauge directly to the fuel pump outlet. With the ignition turned on, the fuel pump should build up pressure and the gauge should show a reading within the specified range. If the pressure is low or there is no reading, the fuel pump may be faulty and need to be replaced.

It is important to note that working on fuel systems can be dangerous, and it is always recommended to seek professional assistance if you are unsure about any part of the process.

Frequently asked questions