Troubleshooting A Rig: Testing Fuel Pressure

If your rig won't start, there could be a range of issues related to fuel, compression, or spark. Before testing fuel pressure, check that there is actually gas in the tank. If there is, the next step is to verify that the fuel pump works. To do this, ask an assistant to turn the ignition switch to On and listen for a two-second whir, hum, or series of rapid clicks as the fuel pump pressurizes the fuel line to the engine. If there is no noise, check the fuel pump fuse and relay. If both are good, check the wiring to the pump. If voltage is present when turned on, then the pump has failed. If there's no voltage at the pump, check the wiring and connections. Once the pump has power and is delivering fuel, you can test the fuel pressure.

Check the Schrader valve

To check the Schrader valve, start by locating the valve on the fuel rail. Remove the Schrader valve cap. You should be able to find it under a fuel rail cover or other plastic engine cover. Once located, check if you can push in the stem with little resistance. If you can, this may indicate that there is an issue with the fuel pump or pressure regulator.

Next, attach a fuel pressure tester fitting to the Schrader valve. Ensure that it is properly threaded on for a leak-proof fit. Turn the ignition to "on", not "start". Observe the psi reading on the tester. If the pressure drops after 5 or 10 minutes, this indicates a leak in the fuel system.

If the pressure holds steady, start the engine and let it idle. The fuel pressure should remain steady, within a few psi of the recommended pressure. Once the engine is warmed up, slowly rev the engine and check that the pressure rises with the RPMs.

If you are unable to access a fuel pressure tester, you can try a few other methods to check the Schrader valve. One option is to disconnect the fuel line and check if fuel is flowing through it. Alternatively, you can try to prime the pump and then check the pressure. However, this may not give an accurate reading.

Test the ignition

If your rig won't start, there could be a problem with your ignition. Here are some steps to help you test it:

Check for Symptoms of a Failing Ignition Switch

Before you start any testing, it's important to look out for some common signs that your ignition switch is faulty. These can include:

• Difficulty starting the engine, such as having to turn the key multiple times or wiggle it.
• A key that feels loose or "off" inside the ignition.
• Electrical problems, such as issues with the headlights, dashboard lights, or other electrical components.
• The car stalls after starting or while driving.
• Trouble powering up accessories like the radio, power windows, or air conditioning.
• The key getting stuck in the ignition.

Test with a Multimeter

To test your ignition switch, you can use a multimeter. Here's how:

• Remove the steering wheel cover to expose the ignition. Refer to your vehicle's instruction manual for guidance, as this process varies depending on the vehicle's make and model.
• Set the multimeter to the 20 DC voltage setting. Turn the dial to "V" or "Ω" to set it to the voltage configuration.
• Plug the probes into the correct ports: black to negative (black port) and red to positive (red port).
• Position the red probe on your ignition switch and the black probe on any exposed, unpainted metal surface in your vehicle.
• Look for the gold or silver terminal on the side of your ignition module. Hold the positive probe against this terminal to test the ignition switch.
• There are usually two terminals (B and S). Test both of them. One is for the battery, and the other is for the ignition switch solenoid.
• If your ignition switch has five terminals, test the B and L terminals in the run position, B and S in the start position, and G, M, and L terminals in the off position.
• Turn the key to the "on" position and check the voltage. A reading of around 11-13 volts indicates a functional ignition switch. If you get a very low reading or nothing at all, it's time to replace the ignition switch.

Test with a Test Light

Alternatively, you can test your ignition switch using a test light. Here's how:

• Disconnect the module's wire connector and the starter solenoid's S terminal after turning the ignition switch off. This will prevent the engine from cranking when you turn the ignition key to the run position.
• Rotate the ignition key and place it in the run position. Probe the red wire connection and the ignition coil's battery terminal to test the voltage.
• Rotate the switch to the start position and probe the module's white wire connector and the ignition coil's battery terminal to examine the voltage.
• If there is no voltage, the circuit and the switch are faulty.

Check the Fuse

Another aspect to test is the fuse connected to your ignition switch. Here's how:

• Locate and open the fuse box. It is usually under the hood, near the steering wheel, or in the glovebox. Refer to your vehicle's manual if needed.
• Identify and remove the starter signal fuse from its port. If the fuses are not labelled, refer to your vehicle's manual to find the correct fuse.
• Inspect the metal strip on the fuse. If it looks burnt or damaged, the fuse needs to be replaced.
• If the metal strip looks okay, test the pins with a multimeter. If you get a resistance of 50-120 ohms (Ω), the fuse is fine. If it's outside this range, the ignition relay fuse needs to be replaced.
• You can also test the ignition relay by swapping the fuse with a known good one and then starting the vehicle. If the vehicle starts, your old fuse was faulty.

Check the fuel pump fuse

If your rig won't start, it's important to check the fuel pump fuse. This is because a blown fuse could be the reason why the fuel pump is not working.

First, make sure your vehicle is turned off and safely parked on a level surface. Then, turn the key so the gauges and warning lights come on, but don't start the engine. You should hear a buzzing sound, which is the electric fuel pump trying to prime the fuel system. This will only run for a few seconds, and then shut off. If you don't hear this sound, your engine has no fuel pressure, and you should check the fuse panel to see if the fuse is blown.

The fuse panel or circuit box is usually located near the battery and is a small black box with a removable lid. Inside the cover, you may find a fuse index, which will tell you where the fuel pump fuse is located. If not, you will need to check your owner's manual. Pull out the fuse and hold it up to see if the element is broken. If it is, you can replace it with a new fuse of the same AMP rating.

Once you have replaced the fuse, repeat the process of turning the key so the gauges and warning lights come on. If you now hear the buzzing sound, you have successfully fixed the problem by replacing the fuse. If you still don't hear the fuel pump, the fuse is not the issue, and you will need to check the fuel pump relay or consider other potential causes of low fuel pressure.

Verify power to the pump with a multimeter

If your rig won't start, it's important to verify power to the pump with a multimeter. This will help you determine if the pump is receiving electricity from the battery and if there are any issues with the electrical system. Here's a step-by-step guide on how to do it:

Step 1: Locate the Fuel Pump Relay

Turn off your vehicle and remove the key from the ignition. The fuel pump relay is usually located in the fuse box under the hood or in the passenger compartment. Consult your owner's manual or a wiring diagram to find the exact location. The relay is typically coloured green or grey and has four or five pins that connect to the wiring harness.

Step 2: Remove the Relay

Pull the relay straight out from the fuse box by gripping it firmly on both sides and pulling it straight up from the terminals. If it doesn't come out easily, try rocking it back and forth gently to loosen the connection. Removing the relay will temporarily disable the fuel pump, so you won't be able to start your engine.

Step 3: Clean the Relay Prongs (If Necessary)

If the relay prongs show signs of rust or corrosion, clean them with a wire brush. Hold the relay upside down and scrape off any corrosion. Alternatively, you can use an electrical contact cleaner and a cloth to remove stubborn corrosion. Clean the terminal ports on the fuse box as well to ensure a solid connection.

Step 4: Understand the Relay Circuit Diagram

Look for a printed diagram on the main body of the relay, which represents the circuit it controls. Identify the two points on the diagram with a box in between them, as these correspond to the power prongs. The prongs you need to test are the ones with a break in the line connecting them. Typically, the power prongs are labelled 85 and 86, while the test prongs are 87 and 30.

Step 5: Set Up Your Multimeter

Set your multimeter to the ohm setting (resistance) to test the relay's circuit. If your multimeter has multiple ohm ranges, choose the lowest one for accuracy. Attach the jumper wires to the positive and negative terminals of your vehicle's battery. Ensure the jumper wires are not touching each other to avoid creating a spark.

Step 6: Connect the Jumper Wires to the Relay

Flip the relay so the prongs face upwards. Connect the jumper wire from the negative battery terminal to the terminal labelled 85, and the wire from the positive terminal to the pin labelled 86. Listen for a clicking sound when you attach the power, indicating that the relay is still functional.

Step 7: Test the Relay's Resistance

Hold the multimeter probes against the remaining two prongs on the relay (30 and 87). The multimeter will measure the resistance of the internal circuit between these prongs. If the circuit has power, the prongs should show no resistance, resulting in a reading of 0 on the multimeter. A reading greater than 0 indicates a faulty circuit.

Step 8: Interpret the Results

If the relay functions correctly and has a reading of 0, your issue may lie elsewhere in the fuel pump or electrical system. If the relay is faulty, replacing it may solve the problem. However, if the relay is functional and you still have issues, further diagnostics may be required.

Check the fuel gauge

If your rig won't start, it's important to check the fuel gauge to ensure it is functioning properly. A faulty fuel gauge can cause a lot of inconveniences, leaving you unsure of how much fuel you have remaining. Here are some detailed steps to help you check the fuel gauge:

First, it's important to understand how a fuel gauge works. The fuel gauge, also known as the fuel level sensor, has two main components: the sensor system (sender) and the indicator (gauge). The sender reads the amount of fuel in the tank and sends that information to the indicator, which then displays the level of fuel on your dashboard.

Now, let's get into the troubleshooting process:

• Observe the fuel gauge needle: If the needle is stuck at the full marker or consistently shifts between the full and empty markers, it indicates a potential issue with the fuel gauge or the sender unit.
• Check the fuel level: If you recently filled up your tank and the gauge is reading empty, or vice versa, it's a clear sign that the fuel gauge is not functioning correctly.
• Perform a self-test: Many modern vehicles have a built-in self-test procedure for the fuel gauge. Refer to your vehicle's owner's manual to find the specific steps for initiating the self-test. If your vehicle has this feature, running the self-test can help determine if the issue lies with the gauge or another component.
• Check other gauges: If other gauges in your instrument cluster are also acting up, it may be a fuse-related problem. Consult your owner's manual to locate and check the fuse for the fuel gauge. If the fuse is blown, replace it and verify if this fixes the issue.
• Test with a multimeter: If you have access to a multimeter, you can perform a more detailed test. Remove the instrument cluster/fuel gauge from the dashboard and check the voltage of the fuel gauge wire with the multimeter set to 20V DC. It should be receiving 12 volts. Inspect all wires for any signs of damage, corrosion, or loose connections, as these issues can lead to inaccurate readings.
• Verify sending unit wiring connections: Inspect the fuel sending unit for any damage, corrosion, or improper seating in the tank. Clean the connectors if necessary to improve conductivity, and ensure a good ground connection. Use the multimeter to check the input and output voltage of the sending unit, referring to the service manual for the proper voltage values. If the voltages are different at each end of the wire, it indicates corrosion or poor wiring between the sending unit and the fuel gauge.
• Check fuel sending unit ohms: If all other checks come back clear, the issue may lie with the fuel sending unit itself. Refer to your vehicle's repair manual for the specific steps to remove the sending unit from the fuel tank. Once removed, use the multimeter set to the Ohms setting to check the resistance performance. Swing the float arm and observe if the Ohms increase or decrease accordingly. If the Ohms are correct but the fuel gauge is still inaccurate, it confirms a wiring issue between the sending unit and the fuel gauge.

By following these steps, you can thoroughly check the fuel gauge and identify any potential issues. Remember, a functioning fuel gauge is crucial for keeping track of your fuel level and avoiding unexpected empty tanks.

Frequently asked questions