Checking Fuel Pressure: Diy Guide For Your 911 Sc

Checking the fuel pressure of a Porsche 911 SC is a complex process that requires careful attention to detail. The Continuous Injection System (CIS) in the Porsche 911 SC is a fuel injection system that requires proper maintenance and calibration to ensure optimal performance. To check the fuel pressure, it is recommended to have a fuel pressure gauge and a basic understanding of the CIS components and their functions. The process involves locating specific parts of the fuel system, such as the fuel distributor, warm-up regulator, and various valves, and performing a series of tests to measure fuel pressure at different engine temperatures and valve positions. It is important to refer to the vehicle service manual or a trusted repair guide for specific instructions and safety precautions when performing these tests. Additionally, some components, such as the fuel distributor and warm-up regulator, are best tested on a fuel flow test bench by a specialist. Overall, checking the fuel pressure in a Porsche 911 SC requires a methodical approach, proper tools, and a good understanding of the CIS system.

The cold control pressure test

• Relieve fuel system pressure.
• Make sure the fuel filter is not clogged. Replace if necessary.
• Clean dirt off the fuel distributor cap.
• Referring to the typical CIS hookup diagram, hook up the tester between the fuel distributor and the control pressure regulator. The hose without the flow control valve should be connected to the center of the fuel distributor. The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.
• Hand-tighten any adapters with O-rings to avoid damage.
• Reactivate the fuel pump and start the engine. Check for leaks.
• Remove air from the system. If your tester has a release valve under the gauge, wrap a rag over the valve and depress the button until the air is released. Do not do this over a hot engine or manifold. If your tester has a bleed-off valve, put the end of the bleed-off valve tubing in a fuel container and bleed until the air is removed. If your tester has none of the above, position the gauge downward as far as the hoses will allow, with the gauge below the hoses and control valve. Operate the fuel pump with the engine off. Open and close the control valve at least five times with the valve in the off and on position for at least 12 seconds.
• When the pressure stabilizes, read the gauge. If the cold control pressure is not correct, the warm-up regulator may be at fault.

The warm control pressure test

To perform the Warm Control Pressure test, the engine must be warm and the valve must be open. The test must be measured with the engine warm.

• Hook up the tester between the fuel distributor and the control pressure regulator. The hose without the flow control valve should be connected to the center of the fuel distributor. The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.
• Reactivate the fuel pump, start the engine, and check for leaks.
• Remove the air from the system. If your tester has a release valve under the gauge, wrap a rag over the valve and depress the button until the air is released. Do not do this over a hot engine or manifold. If your tester has a bleed-off valve, put the end of the bleed-off valve tubing in a fuel container and, with the fuel pump operating, bleed until the air is removed. If your tester has none of the above, position the gauge downward as far as the hoses will allow with the gauge below the hoses and control valve. Operate the fuel pump with the engine off. Open and close the control valve at least five times with the valve in the off and on position at least 12 seconds.
• When the pressure stabilizes, read the gauge. If the pressure is not within the normal range on the control pressure warm test, try adjusting the fuel pressure regulator. If it cannot be adjusted to normal pressures, replace it unless the problem is as follows: if the pressure is low with the engine running and at idle, check to see if the voltage is at least 11.5V at the warm-up regulator plug contacts. If full voltage is available at the plug, then the warm-up regulator may need replacing. If the pressure is too low, test the fuel pump volume. There may also be a blockage in the supply line or leakage in the return line. If the system has none of these, the fuel system pressure needs adjustment. Consult the factory manual or fuel injection manual for the procedure.

The primary pressure test

To start, relieve the fuel system pressure and make sure the fuel filter is not clogged. If it is, replace it. Then, clean dirt off the fuel distributor cap.

Referring to the typical CIS hookup diagram, hook up the tester between the fuel distributor and the control pressure regulator. The hose without the flow control valve should be connected to the centre of the fuel distributor. The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.

Hand-tighten any adapters with O-rings to avoid damaging the O-rings. In a few cases, to get the right combination of threads to connect, the adapters may have to be piggy-backed.

Reactivate the fuel pump and start the engine. Check for leaks. When the tester is connected, remove the air from the system. If your tester has a release valve under the gauge, wrap a rag over the valve and depress the button until the air is released. Do not do this over a hot engine or manifold.

If your tester has a bleed-off valve, put the end of the bleed-off valve tubing in a fuel container and, with the fuel pump operating, bleed until the air is removed. If your tester has none of the above, position the gauge downward as far as the hoses will allow, with the gauge below the hoses and control valve. Operate the fuel pump with the engine off. Open and close the control valve at least five times with the valve in the off and on position at least 12 seconds.

When the pressure stabilises, read the gauge. If the pressure is not correct, the warm-up regulator may be at fault. If the pressure is okay, run the pressure checks.

The rest pressure test

Step 1: Prepare the Tester

• Ensure that the engine is warm.
• Relieve the fuel system pressure.
• Check if the fuel filter is clogged and replace it if necessary.
• Clean any dirt off the fuel distributor cap.
• Refer to the typical CIS hookup diagram and hook up the tester between the fuel distributor and the control pressure regulator.
• The hose without the flow control valve should be connected to the center of the fuel distributor.
• The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.
• Hand-tighten any adapters with O-rings to avoid damage.
• If necessary, piggyback the adapters to get the right combination of threads to connect.

Step 2: Test Fuel Pressure

• Reactivate the fuel pump and start the engine.
• Check for any leaks.
• Remove the air from the system.
• If your tester has a release valve under the gauge, wrap a rag over the valve and depress the button until the air is released. Do not do this over a hot engine or manifold.
• If your tester has a bleed-off valve, put the end of the valve tubing in a fuel container. With the fuel pump operating, bleed until the air is removed.
• If your tester has neither of the above, position the gauge downward as far as the hoses will allow, with the gauge below the hoses and control valve.
• Operate the fuel pump with the engine off.
• Open and close the control valve at least 5 times, with the valve in the off and on position for at least 12 seconds.
• When the pressure stabilizes, read the gauge.

Step 3: Interpret Results

• If the pressure is within the normal range, no further action is required.
• If the rest pressure drops too quickly, check for leaks at O-rings and fuel line connections.
• If there are no external leaks, check for a leaking cold start valve or fuel injectors.
• If there are still no leaks, check for leakage at the fuel pump check valve or at the O-ring on the relief valve in the fuel distributor. Repair or replace as necessary.

The accumulator and check valve

Over time, these components can wear out and cause issues with starting the car, particularly when the engine is cold. If you're experiencing hard starts or notice fuel leaking back into the tank, it might be time to inspect and replace these parts. It's also a good idea to test the fuel system for leaks and ensure that the accumulator and check valve are functioning correctly. This can be done by connecting a pressure gauge and performing tests with the engine on and off to check for any pressure drops or leaks.

When replacing the accumulator and check valve, it's important to follow the correct procedures and specifications for your specific Porsche 911 model and year. Refer to service manuals or seek advice from Porsche specialists to ensure you're using the right parts and methods for your car. Additionally, make sure to only use high-quality replacement parts to ensure the longevity and proper functioning of your fuel system.

Remember, working on fuel systems can be dangerous, so always take the necessary safety precautions and have a fire extinguisher nearby in case of any accidents. It's also advisable to wear protective gear, including eye protection and gloves, when handling fuel system components.

Frequently asked questions