Fuel Pressure Specifications For 2002 Mercedes C320

The fuel pressure for a 2002 Mercedes C320 is a topic that has been discussed on online forums. One user reported that their 2004 model had a fuel pressure of 35 psi when the engine was running, and 0 psi when the engine was switched off. The user suggested that the ideal fuel pressure for the M112 engine should be 50 psi or higher. However, another user suggested that the issue could be related to the pump or regulator, or even a bad injector.

Fuel pressure test

To test the fuel pressure of your 2002 Mercedes C320, you will need to use a fuel pressure tester. This tool consists of a gauge attached to a fuel hose and multiple fittings. The tester will display the pressure in psi on a large gauge visible from inside the vehicle.

Before you buy or rent a fuel pressure tester, there are a few things you can try to diagnose the problem. Firstly, check that there is gas in the tank. If there is, and the car still won't start, verify that the fuel pump is working. 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, as well as the wiring to the pump.

If the fuel pump appears to be working, you can now connect the fuel pressure tester. Make sure to perform these steps in a well-ventilated area with a fire extinguisher nearby, as fuel vapors are highly flammable.

With a cold engine, pop the hood and locate the Schrader valve fitting on the fuel rail. Remove the Schrader valve cap and attach the appropriate fuel pressure tester fitting, ensuring a tight, leakproof fit. Turn the ignition to "On," not Start, and check the psi reading. If the pressure drops over 10 minutes, this indicates a leak in the fuel system.

Once the engine is started and idling, you should see steady fuel pressure, within a few psi of the recommended pressure. The exact fuel pressure for your 2002 Mercedes C320 is not readily available, but a repair manual should specify the correct pressure. Once the engine is warmed up, slowly rev the engine and ensure that the fuel pressure rises with the RPMs.

If your fuel pressure is steady, rises with engine speed, and is at the recommended pressure, then your engine problem does not seem to be fuel-related. However, if you are experiencing low fuel pressure, the fuel filter may be clogged, or the pump could be failing or not receiving power. High fuel pressure could be caused by a clogged or kinked fuel return line, a faulty fuel pump driver module, or a powertrain control module.

Faulty fuel pump

A fuel pump is located inside the fuel tank of a car and has a small electric motor to ensure that pressurised gasoline flows to the engine to power the vehicle. Most fuel pumps will last for the life of the vehicle, but they can occasionally fail.

A faulty fuel pump in a 2002 Mercedes C320 may manifest in the following ways:

• The engine struggles to maintain speed or "chokes"
• Noises, backfires, and a sputtering engine
• Hesitation at start or take-off
• The engine overheating, as a result of the fuel pump overheating
• The \"Check Engine\" light is on
• The car won't start

If you suspect a faulty fuel pump, it is best to consult a mechanic as soon as possible.

In addition to the above symptoms, a 2002 Mercedes C320 with a faulty fuel pump may also exhibit the following:

• The car won't start at the first try, requiring multiple attempts
• When the car finally turns on, it stutters, idles roughly, and there are knocking noises under the hood
• There is no response when pushing the gas pedal, or the car moves slowly when pressing the gas
• Multiple cylinder misfires on most cylinders
• The check engine light is on, with codes indicating a "System too lean - Bank 1" and "System too lean - Bank 2"

It is important to note that the above symptoms could be indicative of other issues with the vehicle, and a proper diagnosis by a qualified mechanic is necessary to determine the exact cause.

Clogged fuel filter

A clogged fuel filter can cause a wide range of issues with your 2002 Mercedes C320. Fuel filters are an important part of the fuel delivery system, trapping contaminants from the fuel tank and preventing them from entering the rest of the fuel system and causing damage.

Mercedes suggests changing your filter every 30,000 miles. A clogged filter can cause problems ranging from a rough-running engine to leaving you stranded on the side of the road. When the fuel filter begins to clog, the engine suffers from fuel starvation, resulting in a significant reduction in power and possible misfires. These conditions may be intermittent or constant, worsening over time. As the issue progresses, the engine may stall immediately after starting, fail to start, hesitate under throttle, or stall at particular angles on hills.

In some cases, a clogged fuel filter can cause the engine to shut down on the highway, making driving unsafe. If your car is exhibiting any of these symptoms, it is important to have the fuel filter checked and replaced if necessary.

The fuel filter on your 2002 Mercedes C320 is located on the underside of the car, behind the rear left side seat. To replace it, you will need to safely lift and support your car, remove the underbody tray to access the filter, and then remove the T25 Torx screw holding the filter in place. It is important to mark the gas lines and take pictures to ensure proper reassembly. Pinch off all four gas lines, remove the hose clamps, and then remove the lines from the filter. Install a new filter, ensuring it faces the correct direction, and check for leaks before reinstalling the underbody tray.

In addition to a clogged fuel filter, there are other potential causes for the issues you are experiencing. For example, a carboned-up throttle body can cause problems with idling, and a faulty mass airflow sensor can also lead to similar issues. It is recommended to have a qualified mechanic diagnose the problem and perform any necessary repairs.

Vacuum leaks

There are many places where vacuum leaks may occur, and they may not always be obvious. Here is a list of places to check for leaks:

• Oil filler cap
• Dipstick
• Valve cover
• Oil dipstick O-ring
• Intake manifold gaskets
• Brake booster system
• Vacuum line going to the booster
• One-way valve
• Grommet that secures the vacuum line to the brake booster
• Brake booster diaphragm
• Rubber boots and hoses around the engine
• Vacuum lines, intake boots, seals, and other small gaskets around the engine
• Secondary air injection pump area
• Hose from the air pump to the bottom of the intake manifold
• Hose from the air pump to the shut-off valve
• Hose from the shut-off to the check valve
• Hose from the check valve to the intake manifold
• Hose from the exhaust gas recirculation valve to the actuator solenoid on the front of the engine
• Vacuum connection from the intake manifold to the fuel pressure regulator
• Central locking system

To check for a vacuum leak, a smoke test can be performed. This involves inducing smoke into the intake manifold so you can detect any leaks.

Another quick way to check for a vacuum leak is to take the oil filler cap off with the engine running. If the system is in good shape, the idle of the engine should drop and the car will run rougher. If there is no change in the vehicle's idle, then you probably have a vacuum leak somewhere in the system.

If you are experiencing issues with your 2002 Mercedes C320, it is recommended to take it to a Mercedes specialist or a trusted mechanic for diagnosis and repair.

Fuel trim values

The oxygen sensors could be likened to the computer's "eyes" that watch the mixture of oxygen in the exhaust. The computer monitors this input from the heated oxygen sensor(s) continuously when in closed-loop. If the o2 sensors inform the engine computer that the exhaust mixture is lean, the computer adds fuel by lengthening the injector pulse, or "on-time", to compensate. Conversely, if the o2 sensors inform the computer that the exhaust is rich, the computer shortens the injector pulse, adding less fuel to compensate in order to bring the rich condition down.

This change in fuel being added or taken away is called Fuel Trim. The oxygen sensors are what drive the fuel trim readings. Changes in o2 sensor voltages cause a direct change in fuel. The short-term fuel trim (STFT) refers to immediate changes in fuel occurring several times per second. The long-term fuel trims (LTFT) are driven by the short-term fuel trims. LTFT refers to changes in STFT but averaged over a longer period of time.

A negative fuel trim percentage indicates a reduction of fuel, while a positive percentage indicates an addition of fuel. A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually, they'll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long-term fuel trim reading will appear to stay the same, giving a long-term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances.

If you experience ST or LT fuel trims that are in the double digits, positively or negatively, this would indicate an abnormal addition or reduction of fuel. This could be due to leaking fuel injectors, an unmetered air leak, or something similar. For example, if the o2 sensors are reading lean due to, say, a vacuum leak, the engine computer will compensate by adding fuel. The STFT will start to climb immediately to reflect the computer adding fuel. While the computer is adding fuel, it still watches the o2 sensors until the o2 sensors are indicating that the lean condition no longer exists and a proper air-to-fuel ratio is met.

The fuel trim values are read by plugging a scan tool into the OBD II diagnostic connector located under the instrument panel (on the driver's side near the steering column). When the key is turned on, the scan tool will initialize and start to communicate with the vehicle's onboard computer. Depending on the tool and the vehicle, it may be necessary to enter the vehicle year, make, model, and engine VIN code before the scan tool can read the data.

Frequently asked questions