Testing A High-Pressure Fuel Pump: Step-By-Step Guide

Testing a high-pressure fuel pump can be done in several ways. One method is to physically measure the fuel pressure with the engine running, using a test port on the fuel rail. Another approach is to monitor the pump electronically with a scantool. If the pump is mechanical, testing it may involve removing it from the vehicle and conducting a bench test. To confirm a pump failure, it is often necessary to replace it with a new one. The specific testing procedure may vary depending on the vehicle's make and model.

Physically measure fuel pressure with the engine running

To physically measure the fuel pressure with the engine running, you will need to install a fuel pressure gauge. Park your car and apply the parking brake. Then, turn off the engine and allow it to cool down. Locate the fuel pressure test port and place a rag underneath to catch any fuel that may be released during the testing process.

Install the pressure tester to the port and start the engine. You should now be able to record the pressure reading. Check the manufacturer's manual for the pressure testing specifications. Some manufacturers recommend checking the pressure with the engine running at a specific RPM. For example, a typical port-injected vehicle requires fuel pressure between 30 and 80 PSI. If your fuel pump does not meet the required pressure specifications, it may be failing to pump fuel to the engine.

If you do not have access to a fuel pressure tester, you can try a few things before renting or buying one. Firstly, check that there is fuel in the tank. Even if the fuel gauge shows a full tank, it could be faulty. Add at least two gallons of fuel and try starting the engine again. If the engine starts, check the fuel gauge for internal failure and replace it if necessary. If the new gauge still shows a high fuel level, the issue may be a failed fuel sending unit in the tank.

Another step you can take is to verify that the fuel pump is working. 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 no noise is heard, this could indicate that the pump is not receiving power or has failed. Check the fuel pump fuse and relay, and if those are functioning, inspect the wiring to the pump.

Monitor electronically with a scantool

Monitoring electronically with a scantool is a modern way to test a high-pressure fuel pump. This method is more efficient than traditional analog and hands-on diagnostic procedures, which often involved a pressure gauge and voltmeter. With a scantool, you can verify if the modules controlling the fuel pump are receiving the correct data, such as oil pressure, crank position, and key position. This includes checking if the serial data bus is communicating effectively with modules like the theft deterrent system and the Body Control Module (BCM).

Late-model vehicles with returnless fuel systems use engine data to vary the speed of the pump, and this can be observed with a scantool as part of the Mode 6 Data. Before connecting the scantool, it is important to perform a visual inspection of the vehicle and verify the customer's complaint to ensure accuracy in the diagnostic process.

Once the scantool is connected, you can pull codes and ensure that the modules are communicating on their respective communication buses. Enhanced or factory scantools can perform a "health check" and even automate tests to confirm the operation of the fuel pump. This information is crucial for developing diagnostic strategies and further tests to resolve any issues.

Factory and enhanced scantools can also monitor pressure transducers on both the high and low sides of the system, providing valuable data on the performance of the fuel pump during different modes of operation. This data can be used to perform cylinder balance tests and diagnose hard-start problems.

Check for issues with the FPCM wiring harness

When checking for issues with the FPCM wiring harness, it is important to conduct a thorough visual inspection of the wiring harness and connectors. Look out for any signs of damage, corrosion, or loose connections. Pay close attention to the pins in the connectors and check for any that may be broken, bent, pushed out, or corroded.

Additionally, you can use a multimeter to test the voltage and resistance at various points in the FPCM's electrical circuit. Abnormal readings could indicate an issue with the FPCM or the fuel pump.

It is also recommended to scan for trouble codes using a diagnostic scan tool. This can help identify any additional codes beyond P1220 or P069E that could provide further insights into the issue.

If you are experiencing issues with the FPCM, it is important to address them promptly to ensure the proper functioning of your vehicle's fuel system.

Check for a faulty crankshaft sensor

The crankshaft position sensor is one of the most critical sensors in your vehicle. It's the only thing in your engine that monitors the position of the crankshaft, which is connected to and works directly with your engine's pistons. Without a functional crankshaft sensor, your engine would not run properly.

• Check engine light illuminating on your dashboard
• Difficulty starting the engine or stalling while driving
• Rough idling and engine misfires
• Increased vibration and rough riding
• Noticeable decline in fuel efficiency

If you're experiencing any of these issues, you can perform the following test to determine if your crankshaft sensor is faulty:

Locate the Crankshaft Sensor

The crankshaft position sensor is typically found near the bottom of the engine by the crankshaft. It may be located in the front or back of the crankshaft on a bell housing or tucked behind something else.

Inspect the Sensor

Look for signs of damage to the housing. It's common for the housing to get burnt or covered in dirt, oil, or other debris, which can cause the sensor to stop working correctly.

Use a Multimeter

If you have a multimeter, set it to the ohms setting and take the sensor's measurement. The meter should read a resistance value anywhere from 200 to 1,000 ohms (or more, depending on the model). If it reads 0 ohms, the sensor needs to be replaced.

Causes of Crankshaft Sensor Damage

The two most common causes of damage to the crankshaft sensor are:

• Melting of the plastic housing due to engine overheating or hot weather conditions.
• Loose, worn-out, or damaged wiring, which disrupts signals sent to and from the sensor.

Check the voltage on the connector on the back of the intake manifold

To check the voltage on the connector on the back of the intake manifold, you will need to locate the connector first. It is usually found on the back of the intake manifold, and in this case, it is the X117 connector.

Once you have located the connector, you can then proceed to test the voltage. There should be three wires connected to the connector: a gray wire, a tan wire, and a yellow wire. The gray wire, which is usually connected to pin 11, is the 5-volt reference voltage wire and should always have 5 volts when the key is turned on. The tan wire, typically connected to pin 5, is the ground wire and should always be grounded. The yellow wire, often connected to pin 12, is the signal wire, and its voltage should be monitored with the key turned on and while cranking the engine. By monitoring the voltage on this wire, you can determine if the sensor is functioning correctly.

Additionally, you can also test the voltage at the high-pressure fuel pump regulator connector. With the key turned on, you should have a voltage reading of around 8.8 volts at this connector. This voltage reading indicates that the computer is supplying power to the regulator and that the circuit is complete.

If the voltage readings on the connector on the back of the intake manifold or the high-pressure fuel pump regulator connector are not within the specified ranges, it may indicate a problem with the wiring, the sensor, or the computer system. Further diagnostics and testing may be required to identify the exact cause of the issue.

Frequently asked questions