Troubleshooting Car Crank Issues: Fuel Pump Pressure

A car may not crank due to a lack of fuel pressure, which can be caused by a faulty fuel pump. A bad fuel pump may still pump fuel, but the vehicle may experience difficulty starting due to a lack of pressure. This can cause the vehicle to take more cranks to start than normal, and in more serious cases, it may require multiple turns of the key before the engine starts. Before replacing the pump, it is advisable to check for a blown fuse and/or low pressure in the fuel line.

Check valve failure

A faulty check valve in the fuel pump can cause a range of issues. The check valve is a crucial component that ensures fuel can only travel in one direction. When it fails, fuel in the lines will siphon back into the tank, resulting in a loss of fuel pressure. This, in turn, leads to a longer cranking time when starting the car, especially in the morning or when the engine is cold.

A bad check valve can cause the vehicle to run poorly, stall, or even fail to start at all. If the car does start but stalls as soon as the fuel pump turns off, this is a strong indicator of a faulty check valve. The lack of pressure allows fuel to flow back into the pump, causing the engine to stall.

To diagnose a faulty check valve, you can perform a simple test. Let the vehicle sit overnight, then, in the morning, turn the key to the "RUN" position for 2-3 seconds without starting the engine. Repeat this process several times, and then try to start the engine. If it starts right up, a faulty check valve is likely the issue. This test works by building up fuel pressure each time you turn the key, and a functioning engine should have enough pressure to start by the third attempt.

Another way to diagnose a check valve issue is to use a fuel pressure gauge to test the amount of fuel pressure while the vehicle is running. If the pressure is lower than the specifications for your car, it could indicate a faulty check valve.

If you determine that the check valve has failed, it cannot be replaced as a separate part. Instead, you will need to replace the entire fuel pump.

Injector issues

One of the most common injector issues is clogging. Fuel injectors can become clogged due to the build-up of rust or other contaminants. This prevents the injectors from successfully supplying fuel to the intake manifold, which in turn inhibits engine performance. Clogged injectors can be caused by poor maintenance, especially when the car is idle.

Dirty injectors are another common issue. Injectors are subject to rapid and repetitive movement, which generates substantial heat. This heat, combined with any fuel additives, can leave a residue that forms a crust, leading to a weak or inconsistent spray of fuel. This can cause the engine to misfire, and will also affect the RPM gauge, giving inconsistent readings.

A related issue is that of restricted injectors. This is caused by contamination and carbon build-up, which restricts the flow of fuel. Restricted injectors can lead to high emissions, poor fuel economy, and poor performance. The spray pattern of the injector is also affected, causing poor atomization of the fuel.

Internal o-ring failure is another possible cause of injector issues. Most injectors contain internal o-rings which keep the fuel from leaking out. If these o-rings fail, the injector will leak fuel externally, usually where the plastic connector meets the metal injector body. This can cause a fuel odor, especially on initial start-up or after the vehicle has been sitting idle for a while.

Another possible cause of injector issues is faulty windings, which can arise from overheating, shorting out, or a break in the wiring. This can prevent the injector from opening, and thus delivering fuel when needed.

Finally, injector issues can also be caused by a faulty spring or poor maintenance, which can prevent the injector from closing properly. This leads to over-delivery of fuel into the engine system, which can be identified by the smell of fuel.

High-pressure fuel pump problems

High-pressure fuel pumps are an essential part of modern fuel systems, but they can also be a source of problems. Here are some common issues with these pumps and their potential causes:

Lack of Maintenance

The most common cause of high-pressure fuel pump failure is a lack of oil changes, which leads to wear between the camshaft lobes and the high-pressure pump follower. This wear prevents the pump from generating sufficient piston movement, resulting in reduced pressure and a lean fuel mixture. Before installing a new pump, it is crucial to inspect the lobes on the camshaft, as a lack of power may persist even with a new pump.

Sensor Malfunction

Direct-injection systems rely on pressure and temperature sensors to determine the position of the high-pressure pump solenoid. While a faulty sensor won't directly cause a pump failure, it can lead to misdiagnosis. These sensors have a ±2% accuracy rate, and their malfunction can impact fuel trims. A failed sensor will trigger a low-pressure safe mode to prevent system damage.

Leaks

The high pressure in direct injectors means leaks can occur, even when the engine is resting. This can cause severe carbon buildup and a rich fuel reading. Leaks may also contribute to a longer cranking cycle and potential wear. Most systems have a specified resting pressure that can be monitored using a scan tool.

Old Calibrations

Engineers are constantly refining fuel systems, and sometimes issues arise in the field that weren't caught during development. There is a direct relationship between pump pressures, camshaft position, and pressure solenoid position, all of which can be calibrated to optimise performance and component life. Ensuring the ECU has the latest calibration can help solve driveability problems and may even prevent the need for pump replacement.

Fuel Pump Pressure Solenoid Failure

High-pressure fuel pumps rely on a solenoid to control volume and pressure. When this solenoid fails, the pump defaults to a low-pressure setting.

Ignoring Warning Signs

Some drivers choose to ignore their check engine light, assuming it will resolve itself with better fuel. However, a direct-injection engine with a high-pressure pump issue will enter a limp or low-pressure mode, leading to reduced performance and potential engine wear.

Wiring issues

If your car is not cranking and you have ruled out issues with the starter, battery, fuel, or gas, the problem could lie with the wiring. Wiring issues can be complex and challenging to diagnose, but here are some potential causes and steps to take to address them:

Firstly, it is important to get your hands on a wiring diagram for your specific vehicle. This will enable you to trace the entire circuit and test all the components involved. A wiring diagram will help you identify potential issues and their locations.

One potential issue could be the ignition switch. It is worth checking if the ignition switch is functioning correctly, as it plays a crucial role in starting the car. If the ignition switch is faulty, it may not be sending the correct signals to the fuel pump, preventing the car from cranking.

Another possibility is a problem with the relays. Relays are electrical switches that control various functions in a vehicle, including the fuel pump. A faulty relay may not be supplying power to the fuel pump, leading to crank issues. Checking and testing the relays can help identify if they are the source of the problem.

In some cases, the issue may lie with the wiring itself. Corroded, damaged, or loose connections can disrupt the power supply to the fuel pump, causing it not to function properly. It is important to inspect the wiring for any signs of damage or wear and make necessary repairs or replacements.

Additionally, it is worth considering if there are any "wiring gremlins" at play. This term refers to mysterious wiring issues that can be challenging to identify and troubleshoot. In such cases, it may be helpful to consult a professional mechanic or technician who has experience dealing with wiring problems. They may have access to specialized tools and knowledge to diagnose and resolve the issue.

When addressing wiring issues, it is crucial to be systematic and thorough. Checking connections, testing components, and referring to the wiring diagram can help pinpoint the problem. In some cases, it may be necessary to replace components or repair damaged wiring to resolve the crank issue.

Faulty ignition switch

A faulty ignition switch can cause a lot of issues with your car engine and should be considered as a potential culprit if you're experiencing problems with cranking. The ignition switch is like the gatekeeper or conductor of your car's engine, deciding which systems get access to power and controlling the ignition process. If it goes rogue, it can cause a lot of chaos.

• Car stalls while driving: If your ignition switch fails while the engine is running, it may cut off power to the ignition and fuel systems, causing the engine to stall.
• Engine refuses to start: The ignition switch plays a crucial role in powering up your car. If it's not working properly, the starter motor, engine controls, and ignition controls may not receive the power they need to start, resulting in a stubborn engine that refuses to fire up.
• Car starts then suddenly stalls: If the ignition switch fails in the "on" position, it may momentarily allow the car to start but will cut off power to the fuel and ignition systems as soon as you move the key from the cranking position to the "on" position.
• Issues with powering on accessories: When you turn the key to the "acc" position, the ignition switch should power on accessories like interior lights and the dashboard. If these accessories don't power on, it could be a sign of a faulty ignition switch or lock cylinder.
• Problems turning or removing the key: If your ignition key gets stuck when you try to turn on the car or take it out, it may indicate a worn-out ignition switch. A bad switch might also cause the engine to keep running even after you've removed the key.

It's important to note that similar issues can be caused by fuse and wiring problems, so a proper diagnosis by a professional technician is recommended. They can help determine if you need to replace the ignition switch or if there's another issue at play.

Frequently asked questions