Checking Fuel Pressure: Volvo 740 Fuel Pump Guide

If you're experiencing issues with your Volvo 740 fuel pump, you may need to check the fuel pressure to diagnose the problem. Checking the fuel pressure can help determine if there are any issues with the fuel delivery system, such as a faulty fuel pump or a clogged fuel line. By performing a fuel pressure test, you can identify whether there is sufficient fuel pressure reaching the engine and take appropriate action to resolve any issues. This may involve replacing the fuel pump, cleaning or replacing the fuel filters, or addressing any leaks in the fuel system.

How to check for fuel leaks

To check for fuel leaks in your car, there are several signs to look out for. Firstly, if you smell gasoline inside your car, this could indicate a fuel leak. While the fuel system is not airtight, strong or constant fumes may suggest small leaks in the fuel tank. Secondly, keep an eye on your fuel gauge. A sudden and significant drop, especially when the car has not been in use, could be a sign of a fuel leak. Lastly, check for any puddles of gas underneath your vehicle or under the fuel tank. Place cardboard or newspaper under the car to help identify any leaks.

If you suspect a fuel leak, it is important to take your car to a mechanic as soon as possible. Do not attempt to fix it yourself unless you are a qualified mechanic, as fuel leaks can be extremely hazardous and may lead to fire or explosion. A professional mechanic will be able to pinpoint the exact cause of the leakage and perform the necessary repairs.

Checking the ignition system

To check the ignition system of your Volvo 740, you can perform the following steps:

• Check for spark at the coil itself. Pull the coil wire partway out and have someone else crank the engine. If there is no spark, the problem is in the distributor's secondary components (cap, rotor, wires). If there is spark, continue to the next step.
• Check for voltage present at the coil low-tension terminals with the key on. If there is no voltage, fix any issues with the wiring and connections. If there is voltage, continue to the next step.
• Check the power stage connector. With the ignition on, there should be 12V at the power stage connector (located behind and below the headlight on the driver's side). If there is no voltage, the power stage connector may be corroded and need to be cleaned or replaced. If there is voltage, continue to the next step.
• Check the Hall sensor in the distributor. Disconnect the leads from the reluctor in the distributor and measure the voltage with a sensitive digital multimeter while cranking the engine. There should be some small voltage. If there is no voltage, the Hall sensor may need to be replaced.
• Check the ignition control module (ICM). The ICM is part of the coil assembly, so you can locate it by finding the coil. The ICM may be faulty if the car is not starting, but this is unlikely as it rarely malfunctions.
• Check the crankshaft position sensor. A faulty crankshaft position sensor can cause issues with starting the engine.
• Check the cap, rotor, and wires. Ensure that they are in good condition and properly connected.
• Check for any error codes stored in the OBD system.
• Check the speed sensor insulation. Ensure that it is in good condition and not damaged.

Testing fuel injectors

Another way is to listen for injector opening and closing. Place a screwdriver against the base of each injector when the engine is running. Place your ear close to the handle of the screwdriver and you should hear a faint clicking sound. This is the injector solenoid opening and closing.

A third method is to use a noid light to verify that the injector pulse is occurring. A noid light is inserted into the injector harness and flashes each time the ECU grounds the injector. It won't tell you much more than the presence or absence of a pulse, but if one injector harness has a weak flash, it indicates a circuit problem.

You can also pull the plugs for observation of combustion conditions within each cylinder. Dark grey/brown indicates normal burn, light grey/white indicates a lean burn, and black and oily usually means a rich burn or oil control problem.

Finally, you can use a digital graphing meter or digital storage oscilloscope to see the waveforms. These meters are not cheap, but they can help diagnose injector and fuel pump problems.

Testing fuel pressure regulator

To test the fuel pressure regulator on a Volvo 740, you can start by checking for signs of leakage. If there is a strong smell of petrol, this could indicate a faulty fuel pressure regulator. You can also try pulling off the vacuum hose after driving and look for any traces of petrol. If there is a dribble of petrol coming out of the regulator 'nipple', then the regulator is faulty.

Another test is to yank the vacuum line off of the FPR and see what comes out. If it has ruptured, gasoline will come out. If nothing comes out at idle, clamp off the fuel return line for a few seconds and see if it squirts then. If there are no squirts and the pressure is steady at around 40 PSI on the schrader valve with the vacuum line hooked up, the regulator is likely okay.

If you have replaced the fuel pump and fuel pressure regulator, but your car is still stalling, this could be due to leaking fuel injectors. You would need to do a fuel bleed-down test to check this. Alternatively, the issue could be with the ignition system, a bad coil, or the ignition control module.

Checking fuel pump relay

To check the fuel pump relay on a Volvo 740, you can try the following methods:

• Check the voltage at the block connector in the rear left cubby hole using an indicator lamp. You should get voltage and pump noise when turning the key and again when turning the engine over.
• Try tapping the relay first.
• Remove the relay and wiggle the contacts with a lollipop stick or small finger. If the engine starts, it's the relay.
• Remove fuses 1 and 11 and jump wire between them. If it buzzes, the in-tank pump is alive. Then, take the fuel pump relay out and jump it between pins 30 and 87/2. If the pumps turn on, it's the relay.
• Check the crank sensor by watching the rev counter for movement after it sees TDC. The ignition computer needs this for spark timing and sends the pulses to the fuel computer, which then enables the pump relay.

The fuel pump relay on the Volvo 740 can be located behind the gear stick, in the engine compartment, or under the bonnet on the near side above the front strut tower.

Frequently asked questions