Troubleshooting A Car That Won't Start: Checking Fuel Pressure

If your car won't start, there could be a range of issues related to fuel, compression, or spark. One common culprit is the fuel pump, which transfers petrol or diesel from the fuel tank to the engine. Before spending money on a new fuel pump, you can troubleshoot the problem by checking the fuel pressure. This can be done by using a fuel pressure tester or a fuel pressure gauge. A fuel pressure tester consists of a gauge attached to a fuel hose and multiple fittings, which connect to the fuel system. A fuel pressure gauge can be connected to the valve on the fuel rail or where your kit requires. You can then turn the key to the on position without starting the vehicle and observe the pressure reading. If the pressure is too low, the vehicle may have trouble starting.

Check the Schrader valve

To check the Schrader valve, you must first locate it. It is usually found on the fuel rail, although some vehicles may have it hidden under a fuel rail cover or another plastic engine cover. Once you have located the Schrader valve, remove the cap and attach the appropriate fuel pressure tester fitting. Ensure that it is threaded on properly for a leak-proof fit.

With the ignition turned to the "on" position, but not started, check the psi reading. A good fuel system will hold pressure well, so if the psi reading remains the same after 5 to 10 minutes, your system is functioning optimally. If the fuel pressure drops, this indicates a leak in the fuel system.

If you are experiencing issues with your Schrader valve, it is recommended to consult a professional mechanic for further diagnosis and repair.

Test the ignition

If your car won't start, there could be an issue with the ignition. Here are some steps to test the ignition:

Check the Ignition Switch

A faulty ignition switch could be the reason your car won't start. The ignition switch carries power from the battery to the starter motor, which is responsible for cranking the engine. If the ignition switch is faulty, the starter motor won't receive power, and the engine won't crank when you turn the ignition switch on. You may not hear any clicking or clunking noise when you start the car. However, the lights and the horn may still work as they have separate wiring harnesses.

To check if the ignition switch is faulty, listen for any clicking or strange noises when you start the car. If you hear these noises, the ignition switch is likely functioning properly, and the issue may lie with the starter motor or another component.

Check the Key and Ignition Lock Cylinder

If the key won't turn in the ignition, there could be an issue with the key itself or the wafers inside the ignition lock cylinder. Try using a spare key to see if it turns. If the spare key also doesn't work, spray a silicon-based lubricant directly into the ignition and try again. Insert and jiggle the key or tap it lightly. If the ignition is filled with gunk, dirt, or debris, a lubricant will help clean the wafers and allow the key to turn.

Check the Steering Wheel

If the steering wheel is locked, it could prevent the ignition from turning. Try wiggling the steering wheel left and right while gently jiggling the ignition key. This might help release the steering lock. Ensure the steering wheel is unlocked before attempting to turn the ignition.

Check the Gear Shift

Modern cars have a safety feature that prevents the ignition from turning if the gear shift isn't in the "Park" or "Neutral" position. Ensure the gear shift is securely in the correct position and try turning the ignition again.

Check the Battery

A dead or faulty battery could be the reason your car won't start. Check if the battery terminals are loose, rusted, or dirty, as this will affect power delivery to the electrical components. Additionally, a weak battery may cause a clicking noise when trying to start the car. Try jump-starting the car or restoring power to the battery to see if it solves the issue.

Check the battery voltage

If your car won't start, it's important to check the battery voltage. This can be done with a multimeter, a device that measures electrical circuits. To test your car battery, follow these steps:

Firstly, locate your vehicle's battery. You can do this by consulting the owner's manual. Once you've found the battery, check for any dirt or corrosion at the positive and negative terminals. The positive terminal usually has a red cover and a "plus" sign, while the negative terminal has a black cover and a "minus" sign. If there is any corrosive buildup, use fine-grit sandpaper to scrub it off. Be sure to wear gloves to protect your skin from harmful chemicals and battery acid.

Now, you can prepare your multimeter. Set it to voltage and ensure it's adjusted to 20 DC volts. If your multimeter does not have incremental settings, simply set it to DC volts.

Next, touch the probes to your battery terminals. Press each probe to the correct terminal, touching negative to negative and positive to positive. The multimeter and battery are likely colour-coded, so the negative terminal and probe will be black, while the positive terminal and probe are red. Take the initial reading with the vehicle off. If the battery is below 12 volts, it needs to be removed and tested further. Starting voltage on any battery is 12.4 volts or more.

If the battery voltage is above 12 volts, turn the vehicle's key to the 'run' position and check the multimeter again. Compare this reading to the voltage figures for your specific car. A fully charged battery will measure at 12.66 volts and above, but 12.6 volts at 80 degrees, 12.588 volts at 30 degrees, and 12.516 volts at 0 degrees are also acceptable readings. A 75% charged battery will measure closer to 12.45 volts, while anything below 12 volts indicates that the battery is discharged.

If you get a reading between 12.3 and 12.5 volts, try charging the battery to full and then turn on the headlights and heater blower motor. The voltage should drop slightly but not drastically. If the car still won't start, do another multimeter test while someone attempts to crank the car. Observe the reading—a good battery will only drop by 1 to 1.5 volts during the load and then quickly return to full charge. If the battery drops to 8 or 9 volts, it may be faulty.

Finally, if you suspect the battery is bad, remove it and bring it in for further testing. It's important to note that jump-starting and driving on a potentially faulty battery can strain the alternator.

Check the engine codes

If your car won't start, there could be a range of issues related to fuel, compression, or spark. The fuel pump is often a likely culprit. Before you spend money on a new fuel pump, it is a good idea to check the engine codes.

If your vehicle shows a check engine light, pull the codes to help diagnose the cause. On newer vehicles, you might be able to check the fuel pressure with a scanner and graph it. Check Engine Light (Codes P0087 and P0190) could appear. If these codes appear, the CPU could be reading low fuel pressure.

If you don't have access to a scanner, the fuel pressure can also be measured with a fuel pressure gauge. Check your repair manual or the internet to find your vehicle's fuel pressure range.

If you have a fuel pressure gauge, connect the gauge to the valve on the fuel rail if it has one, or connect it where your kit requires. Turn the key to the 'ON' position without starting the vehicle and notice the initial measurement. Watch it for 10-15 minutes. If the fuel pressure gauge drops to 5 or 0, there is a leak with the fuel pressure regulator.

If the fuel gauge is connected, turn the key to the 'ON' position (without starting the engine) to build up pressure and force fuel into the fuel line. Release the pressure into a drain pan, reposition the fuel gauge, and take a proper measurement. Turn the key to the 'ON' position again (without starting the engine) and watch the gauge. If the needle drops significantly (like below 30, 20, or 10 psi) over 20-30 minutes, this means the fuel pressure is too low, and the vehicle will have to spend time building the pressure back up to run.

If you don't have a fuel pressure gauge, you can get one at an auto parts store, or you can try a few things before you buy one. First, check that there is actually gas in the tank. Don't trust the fuel gauge, even if it shows a full tank, as the gauge could be faulty. Add at least two gallons to the tank and try another start. If it fires up, check the fuel gauge for internal failure and replace it if needed. If the new gauge shows the same high fuel level, the issue is a failed fuel sending unit in the gas tank. The float arm is stuck, or the resistor has failed. Either way, replace the sending unit.

Test the fuel pressure with a fuel pressure gauge

To test the fuel pressure with a fuel pressure gauge, you'll need to install a fuel pressure tester. This is a simple device consisting of a gauge attached to a fuel hose with multiple fittings. The fittings can be connected to the fuel system of nearly any vehicle.

First, ensure your engine is entirely cold. Pop the hood and find the Schrader valve fitting on the fuel rail. Most vehicles will have one, although it may be hidden under a fuel rail cover or another plastic engine cover. Remove the Schrader valve cap and attach the appropriate fuel pressure tester fitting. Ensure it threads on properly for a leak-proof fit.

Next, turn the ignition to "on", not start. Check the psi reading and wait, watching for a drop in psi that would indicate a leak in the system. If the reading remains the same after 5-10 minutes, the system is holding pressure well. If the fuel pressure drops over this time, there is a leak in the fuel system.

Now, start the engine and let it idle. You should see a steady fuel pressure, within a few psi of the recommended pressure for your vehicle. You can find this information in your car's owner's manual or a repair manual. Once the engine is warmed up, give the engine a slow rev, checking that the pressure rises with the RPMs.

If your fuel pressure holds steady, rises with engine speed, and is at the recommended pressure, your engine problem is likely not fuel-related. If you are experiencing zero fuel pressure, this means the pump is dead or not getting power. Check the fuel pump fuse, then verify power to the pump with a multimeter. If the pump is receiving power, it will need to be replaced.

Low fuel pressure could be caused by a clogged fuel filter or a failing pump. If your fuel filter is serviceable, try replacing it. Low fuel pressure could also be caused by improper tank venting or a loose gas cap. Check the gasket on the gas cap and ensure it is not damaged, tightening it until it clicks.

High fuel pressure can be caused by a clogged or kinked fuel return line, a faulty fuel pump driver module, or a faulty powertrain control module. These issues would likely be accompanied by a "check engine" light. High fuel pressure can also be caused by a faulty fuel pressure regulator.

If you are unsure about how to interpret your fuel pressure readings, it may be best to consult a professional mechanic.

Frequently asked questions