Checking Fuel Pressure: Diy Guide For Your E30

Checking the fuel pressure on an E30 is a simple process that can help diagnose a number of issues. The fuel pressure regulator is located on one end of the fuel rail, which holds the fuel injectors in place. To test the regulator, a fuel pressure gauge must be connected to the Schrader valve or test port on the fuel rail. If the vehicle does not have a Schrader valve, the gauge can be connected directly to the fuel inlet line or a T-adapter. Once the gauge is connected, the engine should be started and allowed to idle. After shutting off the engine, the fuel pressure should hold to specifications for approximately five minutes. If the pressure drops, this could indicate a leaking fuel injector, a faulty fuel pump, or a problem with the fuel pressure regulator itself.

Locating the fuel pressure regulator

The fuel pressure regulator on an E30 is typically located near the thermostat housing in the engine bay. It is connected to the fuel rail, which is the metal tube that carries fuel to the injectors. On some E30 models, the FPR may be located on the back of the fuel rail, under a cover.

To access the FPR, you may need to remove some components, such as the inlet manifold or a cover, depending on your specific model. It is important to refer to a repair manual or seek advice from experienced E30 enthusiasts or mechanics if you are unsure about the exact location and procedure for accessing the FPR.

When working on the fuel system, it is crucial to take safety precautions. Fuel is highly flammable and under pressure, so wear safety glasses and release the pressure in the system before disconnecting any lines to avoid fuel spray. It is also recommended to have a fire extinguisher nearby as an extra precaution.

Additionally, be cautious when working with the FPR, as it can be sensitive to mishandling. Ensure that the fuel lines are connected correctly, as reversing the lines can damage the FPR. If you need to replace the FPR, it is advisable to use a genuine OEM part or a high-quality aftermarket alternative to ensure reliability.

Checking for fuel leaks

Firstly, it's important to note that fuel leaks can be dangerous, so it's recommended to wear safety gear such as gloves and eye protection. Begin by parking your car on a level surface and ensuring that the engine is cool. Fuel leaks can be caused by various factors, including faulty fuel lines, a damaged fuel tank, or a malfunctioning fuel pump. Here are the steps to follow:

• Inspect the area under the car: Get under the car and look for any signs of fuel leakage. Check the fuel lines, fuel tank, and fuel pump for any cracks, holes, or wet spots that indicate a leak.
• Check the rubber hoses and hose clamps: Follow the hoses coming off the inline fuel pump that run back up to the tank. Look and feel around for any wet or cracked hoses. Tighten any loose hose clamps.
• Inspect the fuel filler hose and cap: The fuel filler hose is a common source of leaks. Check if it is securely clamped and in good condition. Also, inspect the fuel cap to ensure it seals properly.
• Pull up the rear bench seat: As suggested by some E30 owners, pull up the rear bench seat and unscrew the access cover(s) to look for leaks from the fuel pump and level sender.
• Check the engine bay: With the engine off, open the hood and inspect the fuel hoses in the engine bay on the driver's side. Look for cracks or signs of leakage.
• Perform a pressure test: If you suspect a fuel leak, you can perform a fuel pressure test to confirm. Connect a fuel pressure gauge to the fuel rail or the supply line before the rail. Start the engine and monitor the pressure. A sudden drop in pressure or no pressure at all could indicate a leak.
• Address the leak: If you locate the source of the leak, it's important to fix it immediately. Depending on the cause, you may need to replace the fuel lines, repair or replace the fuel tank, or replace the fuel pump.

Remember to work with a qualified mechanic if you're unsure about any of these steps, and always prioritize your safety when working on your vehicle.

Testing the fuel pressure regulator

Step 1: Check for External Signs of Faulty Fuel Pressure Regulator

Before diving into more complex tests, it's a good idea to start with a visual inspection for any signs of a faulty fuel pressure regulator. Look for signs of fuel leaks around the regulator or check if there is any fuel in the vacuum hose connected to the regulator. If you notice any leaks or fuel in the vacuum hose, it's a strong indication that the regulator's diaphragm may be ruptured and needs replacement.

Step 2: Monitor Engine Behaviour

Pay attention to how your engine behaves, especially during cold starts or after the car has been sitting for an extended period. Hard starts, excessive smoke, or rough idling can be indicative of fuel system issues, including a faulty fuel pressure regulator. However, these symptoms could also be caused by other factors, so further testing is necessary.

Step 3: Use a Fuel Pressure Gauge

One of the most effective ways to test the fuel pressure regulator is by utilising a fuel pressure gauge. You can either rent one from an auto parts store or purchase an inexpensive one. Connect the gauge to the fuel line leading to the fuel rail. Ensure you place the gauge before the fuel rail and not after it. Once the gauge is connected, start the engine and monitor the fuel pressure.

Step 4: Observe Pressure Changes

With the engine running, observe the pressure changes on the gauge. The fuel pressure should increase slightly as you rev the engine and then return to normal. If there is no change in fuel pressure or the pressure drops below specifications, it could indicate a stuck or faulty fuel pressure regulator.

Step 5: Remove the Vacuum Hose

For further confirmation, remove the vacuum hose from the fuel pressure regulator while the engine is running. If removing the vacuum hose causes the engine to rev up significantly, it suggests that the regulator is not maintaining the correct fuel pressure. Additionally, you can suck on the vacuum hose to check for fuel. If you taste fuel, it confirms a ruptured diaphragm in the regulator.

Step 6: Check Fuel Pressure Retention

Turn off the engine and observe the fuel pressure gauge. The fuel pressure should remain relatively stable for at least an hour. If the pressure drops significantly, it could indicate a faulty regulator or leaking injectors.

Step 7: Check for Leaking Injectors

Let the car sit overnight with the ignition off. In the morning, remove the spark plugs and have an assistant crank the engine. If you smell fuel or notice fuel spraying out of the cylinders, it indicates leaking injectors.

Step 8: Replace the Fuel Pressure Regulator

If, after performing these tests, you suspect that the fuel pressure regulator is faulty, replace it with a new one. It is generally recommended to use a genuine BMW or OEM replacement part to ensure proper fit and function.

By following these steps, you can effectively test the fuel pressure regulator on your E30 and identify any issues related to it. Remember to exercise caution when working with fuel systems, and if you're unsure, seek assistance from a qualified mechanic.

Testing for maximum pressure

• Connect the fuel pressure gauge to the fuel system as you did in the previous section.
• Place a rag over the fuel incoming line (hose) and another rag over the fuel return line (hose). If you need help locating these lines, consult the repair manual for your particular vehicle model.
• Have an assistant start the engine, let it idle for a minute, and then turn it off.
• As the engine turns off, use a pair of slip joint or vise grip pliers to squeeze and block the incoming and return lines. The rag should be between the pliers and fuel line to prevent damage to the hose.
• Note the fuel pressure gauge reading for a few minutes.

If pressure remains steady, the fault is probably in the fuel pump anti-drain valve. If pressure still drops, you have either a leaking fuel injector or a bad fuel pressure regulator.

Troubleshooting a no-start issue

Understanding the Issue

Firstly, it's important to distinguish between a no-crank and a no-start condition. A no-crank situation typically indicates issues with the battery, starter motor, or other power-related problems. On the other hand, a no-start issue suggests that one or more of the essential components for combustion are missing.

Checking for Spark

The first step is to check for a spark, which can be done using an inline spark tester tool or a more traditional method with a spark plug or screwdriver. If there's no spark, move on to inspecting the following:

• ECU (DME)
• Crankshaft Position Sensor (CPS)
• Spark plugs

Testing the CPS

The CPS is a critical sensor that provides timing data to the ECU. To locate it, look near the cold side coolant hose at the front of the engine. Remove it with a 5 mm Allen key and disconnect the wire. Use a multimeter to test resistance between the two pins, aiming for around 500 Ohms. Values outside the range of 470-550 Ohms indicate a faulty CPS.

Checking the Ignition Coil

The E30's single ignition coil provides spark for all six cylinders. Test the two input points with a multimeter to check for voltage. If there's power, use the screwdriver trick to check for a spark.

Inspecting the Distributor

Remove the distributor cap and spark plug wires, then examine the rotor inside for any wear. Ensure that the wires are making solid contact with the distributor cap.

Checking Relays and Fuses

Focus on the two unloader relays first, as they can cause no-start issues. If they're functioning, move on to the main relay and fuel pump relay. Test the relays by listening for a strong clicking sound when turning the key to the accessory position.

Checking for Fuel

Ensure there's fuel in your car, as a faulty fuel gauge or empty tank can be the culprit. Listen for the fuel pump engaging when turning the key to accessory mode. If you can't hear it, inspect the fuel pump and fuel pump relay.

Testing Fuel Pressure

Remove the fuel line from the fuel rail and crank the engine. If there's no fuel or insufficient pressure, you may have a faulty fuel pump or fuel pump relay. Install a fuel pressure gauge between the pumps and fuel rail for a more accurate reading.

Further Troubleshooting

If the issue persists, start checking individual lines for bare wires touching the body of the car or faulty grounds. Use quality BMW parts for any replacements, as this can impact the performance and longevity of your repairs.

Frequently asked questions