Replacing The Fuel Pump In Your 2009 Chevrolet Cobalt

Replacing the fuel pump on a 2009 Chevrolet Cobalt involves dropping the fuel tank, but it's a job that can be done at home. Before you start, it's important to diagnose the fuel pump to ensure it needs replacing. Check for a bad relay, fuse, or circuit, and ensure power is getting to the pump. If the pump is definitely faulty, you'll need to remove the fuel tank from the vehicle to access the pump. This involves disconnecting the filler neck, tank support straps, and insulator strips, before lowering the tank. You can then disconnect the fuel feed and vapour hoses, electrical connectors, and remove the fuel sender assembly. To install the new pump, simply reverse the process.

Diagnose the fuel pump before getting into it

Before replacing the fuel pump on your 2009 Chevrolet Cobalt, it is important to diagnose the issue to ensure that the fuel pump is indeed the problem. Here are some detailed instructions to help you with the diagnosis:

Part 1: Check whether the problem is fuel-related

• If your engine won't start: Listen for the fuel pump by putting your ear near the fuel tank while a helper turns the ignition key to the "on" position. If the pump is working properly, you should hear it.
• Whack the fuel tank gently with a rubber mallet while a helper cranks the engine. If the vehicle starts, it is likely that the electric motor inside the pump is faulty.
• Use starter fluid (at your own risk): Remove the air intake and spray starter fluid into the throttle body while a helper cranks the engine. If the engine starts momentarily, it indicates a fuel-related problem, possibly a bad pump.
• Check for diagnostic trouble codes (DTCs) with a scanner: A faulty pump may set DTCs in your car's computer, either directly related to the fuel pump or indicating an air/fuel ratio problem.
• Check fuel trim with a scan tool: If the engine is running, check the short-term fuel trim (STFT). Normally, fuel trim readings should be between -10 and 10. If the fuel trim is above 10, it means the engine is running lean, and the fuel pump may not be delivering enough fuel.

Part 2: Advanced tests

• Measure current draw with an oscilloscope: Connect a low amp clamp probe to the pump's power wire and observe the waveform pattern on an oscilloscope. A good pump should produce a pattern of even "humps." If the pump is bad, the humps will be jagged and uneven.
• Use a professional-grade scan tool: Some high-end scan tools allow remote fuel pump testing. You can activate the pump with the push of a button to see if it runs.

Part 3: Checking fuel pressure and/or volume

Checking the fuel pressure and volume will help determine if enough fuel is reaching the engine. This can be done using a mechanical fuel pressure gauge, which is inexpensive and readily available. Here are the steps:

• Turn the ignition to the "on" position (key on, engine off) and connect the gauge as outlined in your repair manual.
• Note the reading on the gauge and compare it to the specifications listed in your repair manual. If the reading is significantly different from the specifications, you may have a bad fuel pump.
• Also, check if the pressure holds as outlined in your repair manual. If the pressure bleeds off too quickly, there is a fuel-related problem, such as a bad pump check valve or faulty regulator.

Additionally, you can perform a fuel volume test to measure the volume of fuel delivered over a specified interval. This can be done using a fuel pressure gauge or by disconnecting the fuel return line and connecting it to a container. Consult your repair manual for specific procedures and specifications.

Part 4: Before condemning the pump...

Before concluding that the fuel pump is the issue, there are a few other things to check:

• Check the fuel pump electrical circuit: In older continuous-style fuel systems, the engine control module (ECM) controls the fuel pump via a relay. Newer returnless fuel systems use a fuel pump control module (FPCM). Ensure that everything within the control system is functioning properly.
• Check the fuel pressure regulator: This applies to continuous fuel systems. Disconnect the attached vacuum hose and see if the pressure increases. If not, the regulator or its vacuum supply may be faulty.
• Check the fuel filter: Continuous fuel systems have an external filter that is relatively easy to replace. Rather than testing the filter, it may be easier to install a new one and observe if there are any improvements.

In conclusion, by performing these diagnostic tests, you can determine whether the issue with your 2009 Chevrolet Cobalt is fuel-related and, more specifically, if it is due to a faulty fuel pump. If the fuel pump is indeed the problem, you may need to replace it or consult a mechanic for further advice.

Remove the fuel tank

To remove the fuel tank from a 2009 Chevrolet Cobalt, first make sure to diagnose the fuel pump before getting into it. It may have a bad relay, bad fuse, or bad circuit. Ensure power is getting to the pump, and power it externally if necessary.

Next, drain the fuel from the tank. Get the car high enough that you can work on it, and remove the fuel neck hose at the fuel neck. Disconnect the filler neck from the tank and support the tank. Remove the tank support straps and insulator strips, and then remove the frame-mounted bracket. Lower the fuel tank shield, and then lower the fuel tank enough to gain access to the fuel and electrical connections. Disconnect the fuel feed and vapor hoses, and then disconnect the electrical connectors.

Now you can remove the fuel tank.

Drop the fuel tank

Dropping the fuel tank on a 2009 Chevrolet Cobalt is not too difficult, but it is important to make sure that the fuel pump has been correctly diagnosed and that it is at fault. Before dropping the tank, check for a bad relay, fuse, or circuit. Ensure power is getting to the pump, and power it externally if necessary.

To drop the fuel tank, first drain the fuel from the tank as much as possible. Then, raise and safely support the vehicle, ensuring it is high enough to work under. Loosen the fuel neck hose at the fuel neck and disconnect the filler neck from the tank. Support the tank and remove the tank support straps and insulator strips. Remove the frame-mounted bracket, lower the fuel tank shield, and then lower the fuel tank enough to access the fuel and electrical connections. Disconnect the fuel feed and vapor hoses, as well as the electrical connectors.

Now the fuel tank is ready to be removed from the vehicle. It is important to note that the fuel pump is bolted inside the tank, so you will need to twist the ring to remove the pump.

Signs of a failing fuel pump

A failing fuel pump will cause performance and drivability issues with your vehicle. Here are some signs that your 2009 Chevrolet Cobalt's fuel pump may be failing:

• The engine sputters or struggles to maintain speed in normal driving.
• The car stalls unexpectedly.
• The engine surges while driving, with speed spikes and drops, even though you haven't touched the gas pedal or the brake.
• You hear a loud whining noise coming from the fuel tank. A normal, functional fuel pump makes a low hum.
• The car won't start, or hesitates before starting.
• The engine backfires.
• The engine overheats.
• The vehicle loses power when driving up steep inclines or when loaded with cargo.
• You experience lower fuel efficiency and find yourself making more trips to the gas station.

If you notice any of these issues, it's best to take your vehicle to a qualified mechanic as soon as possible.

How does a fuel pump work?

The fuel pump is an essential component of a car's fuel delivery system. It is usually located inside the fuel tank, although some older vehicles may have it mounted on the engine or on the frame/subframe of the vehicle. The pump draws fuel (gasoline or diesel) from the tank and sends it through fuel lines to the engine. This process ensures that pressurised fuel flows to the engine to power the vehicle.

There are two main types of fuel pumps: mechanical and electric. Mechanical pumps are driven by the camshaft or a special shaft connected to the crankshaft. They use an actuating lever that moves up and down to operate a diaphragm, which creates suction to draw fuel into the pump through a one-way valve. The diaphragm then expels the fuel out of the chamber, and it cannot go back through the first valve, so it exits through another valve leading to the carburettor.

Electric pumps, on the other hand, are more commonly used in modern vehicles. They are typically located inside the fuel tank and are powered by a 12-volt electric pump submerged in the fuel. Electric pumps have a similar diaphragm mechanism to mechanical pumps, but instead of a camshaft, they use a solenoid (an electromagnetic switch) to operate the diaphragm. The solenoid attracts an iron rod that pulls the diaphragm down, drawing fuel into the chamber. When the iron rod reaches the end of its travel, it breaks the current to the electromagnet, relaxing the pull on the diaphragm. The diaphragm then springs back up, pulling the rod away from the contacts and allowing the solenoid to pull the rod and diaphragm down again.

In addition to the pump itself, a fuel delivery system also includes hoses, sensors, and relays. While the pump is typically the component that fails and needs to be replaced, issues with these other parts can also affect the system's performance.

Frequently asked questions