Restarting Your Engine After Fuel Pressure Loss: A Guide

Restarting an engine after fuel pressure loss can be a challenging task. There are several factors that can cause fuel pressure loss, such as a faulty fuel pump, a leaking injector, or a bad check valve. To diagnose the issue, one can perform tests such as clamping the fuel rail inlet hose or return line, checking the vacuum line for fuel odour, or deadheading the pump. It is important to note that fuel pressure loss overnight is normal, and it should not affect the engine's ability to start quickly. However, if the issue persists and the engine takes longer to start, it may be necessary to replace the fuel pump or pressure regulator.

Check for a faulty check valve

A faulty check valve can cause fuel to drain back into the tank overnight, making it difficult to start your engine in the morning. If your engine starts up normally when warm but takes multiple attempts to start in the morning, this may be due to a bad check valve. You can test for this by letting the vehicle sit overnight, then turning the key to the 'RUN' position for 2-3 seconds, but not starting the engine. Repeat this three times, then try starting the engine. If it starts right up, a bad check valve is likely the issue.

To check for a faulty check valve, you will need to test the fuel pressure. You can do this by connecting a fuel pressure gauge to the test port or a testing location on the fuel line. Turn the key on several times (with the engine off) to build pressure and see if the fuel pump reaches the specified pressure. If it does, take the vehicle for a test drive to ensure the pressure is maintained when under load.

Next, measure how much fuel the pump delivers. Activate the pump and measure the fuel it delivers in 30 seconds. Then, compare the fuel delivery volume to the car maker’s specifications. If it fails to deliver the correct volume, a bad check valve may be the issue and you will need to replace the fuel pump.

Another way to check for a faulty check valve is to perform a fuel pump leak-down test. Repeat the test above to build pressure, then leave the gauge attached and leave the vehicle overnight. If the fuel system loses more than 5-10 psi, the check valve is faulty and the fuel pump must be replaced.

It's important to note that a failing check valve will usually emit warning signs. For example, it may start to vibrate or make noises as it breaks down. Additionally, valves will start to stick and leak, with leaks stemming from a damaged seat or disc, or contaminants in the pipeline.

Test for a leaking fuel injector

To test for a leaking fuel injector, you can start the car and spray a small amount of carb cleaner around the injector O-ring. If the car surges, you have a leak.

Alternatively, you can perform the following steps:

• Start the engine and let it run on idle. Inspect the fuel injectors individually for leaks. If there are any external leaks, the fuel injector O-ring is likely the cause.
• Turn off the engine and remove the battery negative terminal. Remove the air filter box by unscrewing the fasteners holding it.
• Depending on your car model, disconnect the throttle cable or unplug the throttle socket. Ensure you gently remove all the wires along the way.
• Disconnect the socket on the injectors. Unbolt the fuel rail and gently pull off the rail with an injector remover. Ensure the fuel lines remain on the fuel rail to deliver adequate fuel pressure from the fuel pump.
• Measure the fuel pressure using a syringe that has milliliters.
• Use a multimeter to test the voltage on the injector sockets. Numbers from 3.70 to 3.89 are okay.
• Remove the fuel fuse and inspect it. You will see PIN 87 and 30, which are the main fuel lines (these numbers may differ between cars). Contact the fuse to keep the fuel running steadily.
• Send a current to the injector and examine the spraying rate of the injectors individually. Use the syringe to determine the level of fuel entering the container during this process. Allow the fuel to reach 30-50 milliliters for greater accuracy.
• Record the time taken for all the injectors to fill the milliliter container. If any injector is spraying excess fuel, it is leaking.

If you discover a leaking fuel injector, you should get a new one and replace it.

Test the fuel pump

To test the fuel pump, you will need to locate the pump itself, which is usually inside the fuel tank. Many vehicles have an access panel in the trunk or inside the car, but some require the fuel tank to be lowered first.

You can then perform an electrical test to check the power supply to the pump. Check your owner's manual for the location of the fuse box, then find the fuse that corresponds to the fuel pump. If it is blown, it will be broken or burned. If the fuse looks good, check the rest of the fuses related to the fuel system and replace any that are blown. If no fuses are blown, listen out for the fuel pump relay clicking on when you turn the key.

If the electrical test reveals nothing, you can then perform a fuel pressure test. Get a fuel pressure gauge and hook it up to the fuel pump test fitting, which is usually near the fuel injectors. Have a helper rev the engine and check the pressure at idle speed and at the rated speed listed in your pump specifications. If the needle doesn't move or goes down below specifications, the fuel pump needs to be replaced.

Check the fuel regulator

Checking the fuel pressure regulator is an important step in diagnosing fuel pressure loss. The regulator is responsible for maintaining the appropriate fuel pressure in the fuel rail, ensuring the correct amount of fuel is delivered to the engine. Here are some detailed steps and signs to look for when checking the fuel pressure regulator:

Signs of a Faulty Fuel Pressure Regulator:

• Misfiring Engine: One common symptom of a faulty regulator is an engine that misfires during idle or acceleration. This can cause the engine to sputter and sound irregular. However, it's important to note that misfires can also be caused by other issues, so a proper diagnosis is necessary before replacing the regulator.
• Loss in Acceleration: A faulty regulator can result in incorrect fuel pressure, leading to a too rich or too lean air-fuel mixture. This, in turn, causes a drop in acceleration and makes the car feel slower.
• Check Engine Light: Modern cars have monitoring systems that detect sensor failures, and a faulty regulator can trigger the check engine light. A trouble code will be stored in the engine control module's memory, indicating a potential issue with the regulator.
• Fuel Leakage: A damaged or broken diaphragm or outer seal in the regulator can cause fuel leakage, leading to performance problems and unpleasant smells. Fuel leaks are dangerous as they can result in a car fire.
• Black Smoke from the Exhaust: A rich air-fuel mixture, often caused by a faulty regulator, can lead to black smoke from the exhaust. If you notice black or gray smoke and other symptoms, it's likely an issue with the regulator.
• Vacuum Hose Filled with Gasoline: A defective regulator diaphragm can cause fuel to enter the vacuum system instead of the engine. Check the vacuum hose connection to the regulator for the presence of gasoline, indicating a faulty regulator.
• Gasoline Smell from the Dipstick: A rich air-fuel mixture caused by a faulty regulator can result in unburned fuel flowing into the oil pan, which you may notice when checking the engine oil dipstick.

Testing the Fuel Pressure Regulator:

To test the regulator, you'll need a fuel pressure gauge and a repair manual for your car. Here are the steps to follow:

• Connect the fuel pressure gauge to the fuel rail.
• Let the engine run with the gauge connected.
• Disconnect the vacuum hose from the regulator.
• With the hose disconnected, observe the fuel system pressure. It should increase by 8 to 10 psi. If there is no change, it indicates a defective regulator.
• Also, check the fuel pressure against the manufacturer's specifications in the repair manual.
• Additionally, you can use an OBD2 scanner to check the regulator on newer vehicles.

Replacing the Fuel Pressure Regulator:

If you determine that the regulator needs to be replaced, here are some important considerations:

• The average replacement cost is between $80 and $500, including parts and labor.
• In some car models, the regulator cannot be replaced alone, and you may need to replace the entire fuel pressure rail.
• For V engines, there may be multiple regulators, increasing the replacement cost.
• In some cases, the regulator is located near the fuel pump in the fuel tank, making the replacement more difficult and expensive.
• It's recommended to replace the hose clamps for the fuel lines and the vacuum hose during the replacement.
• Always refer to a repair manual or seek professional assistance if you're unsure about the replacement process.

Check for fuel leaks

Checking for fuel leaks can be a tricky process, but it is an important part of maintaining your vehicle and ensuring your safety. Here are some detailed steps to help you check for fuel leaks:

Identify Signs of a Leaking Fuel Line:

• Strange Odours: One of the earliest signs of a fuel leak is smelling gasoline inside your car. This distinct odour indicates that fuel is escaping from the fuel line. Gaseous fumes can cause headaches and nausea, and the risk of fire or health hazards makes this urgent.
• Visible Leaks: Check for fuel leaks on the ground where your car was parked, especially after long drives or when the vehicle has been sitting for a while. Visible leaks can attract dust and debris, leading to further engine problems.
• Reduced Engine Performance: A leaking fuel line can cause issues like difficulty starting the engine, rough idling, and unexpected power loss. This is due to an imbalance of air and fuel in the engine's combustion chamber, which can damage the engine.
• Hissing Sounds: A damaged fuel line may produce a hissing sound similar to a tyre releasing air. This is often noticeable when the engine is idle or has just been turned off, and it may be accompanied by a drop in fuel efficiency.
• Check Engine Light: Sensors may trigger the check engine light due to fuel line issues. If this light comes on, especially with other problems like odours or performance issues, it's worth inspecting the fuel line.

Inspections and Tests:

• Visual Inspection: Regularly inspect the entire fuel line for any cracks, wear, or damage. Pay close attention to connections and junctions, as these are common leak points.
• Pressure Testing: Mechanics often use pressure testing to identify leaks in the fuel system. This can confirm the integrity of your fuel line if you suspect an issue.
• Check for Corrosion: Corrosion is a common cause of fuel line damage, especially in older vehicles or those exposed to harsh environments.
• Diagnostic Tools: Automotive service centres have specialised tools to detect fuel line issues.

Finding the Source of the Leak:

• Blocking Off Sections: To pinpoint the leak, try blocking off sections of the fuel line and pressurising them individually. This will help isolate the problem area.
• Using Soapy Water: When pressurising sections of the fuel line, apply soapy water to connections and junctions. Leaks will cause bubbles to form, helping you identify the source.
• Dye Test: For diesel fuel systems, a dye test can be performed to find high-pressure leaks. This involves adding dye to the fuel and using a black light to inspect injectors and fuel lines for signs of leakage.
• Checking Injectors: Fuel injectors can sometimes be the source of leaks. Inspect the injector o-rings and spill pipes (rubber hoses) for any signs of leakage or damp spots.
• Return Line Inspection: While return lines usually operate at low pressure, they can still allow air back into the system. Inspect the return line connection at the tank and the entire line for any signs of leakage.

Remember, if you suspect a fuel leak, it's important to consult a professional mechanic as soon as possible. They have the experience and tools to accurately diagnose and repair fuel line issues.

Frequently asked questions