Fuel Pressure Regulator: 90 W124 Mercedes 300E Location Guide

The fuel pressure regulator in a 1990 W124 Mercedes 300E is located behind the air filter housing. To access it, you'll need to remove the air filter housing by unscrewing the three 10mm nuts that hold it in place. Once you've located the fuel pressure regulator, you can replace it by cracking the lines to relieve fuel pressure and then unscrewing the bolts to remove the old part. When installing the new regulator, be sure to hand-tighten all fittings before using any tools to ensure a snug fit.

Fuel pressure regulator replacement

The fuel pressure regulator in a 1990 W124 Mercedes 300E is located on the fuel rail. You can identify it by its Schrader valve and a vacuum line connected to a nipple on the valve.

If you need to replace the fuel pressure regulator, the project will take about an hour and you will need a circlip tool and a flathead screwdriver. You should also work on a cold engine in a well-ventilated area, keeping a fire extinguisher nearby.

• Relieve the fuel system of any pressure. Remove the fuel pump relay, which is located in the upper right side of the engine bay behind the battery. Crank the engine over a few times to draw out the fuel and relieve the pressure.
• Remove the plastic cover protecting the wiring and fuel rail.
• Open the cap on the Schrader valve using a small flathead screwdriver. Gently press the release valve. Wrap a rag around the valve to catch any escaping fuel.
• Pull the vacuum line off the nipple on the valve. Clean the top of the valve to prevent dirt or debris from entering the fuel system.
• Use circlip pliers to remove the circlip from the valve.
• Pull the valve straight up and out of its housing.
• Install the new regulator by putting a little clean gas on the O-rings and pressing the valve down into the housing with hand pressure.

Please note that working on the fuel system can be dangerous, so it is important to take the necessary precautions and be prepared for any potential issues.

Fuel system safety

The fuel pressure regulator in a 1990 W124 Mercedes 300E is located on the fuel rail. You can identify it by its yellow colour.

Fuel systems can be dangerous, so it's important to take precautions when working on one. Here are some safety tips to keep in mind:

• Work in a well-ventilated area.
• Keep a fire extinguisher nearby and know how to use it.
• Avoid any sparks or open flames.
• Don't smoke.
• Relieve the fuel system of pressure before you start work. You can do this by removing the fuel pump relay and cranking the engine over a few times. The fuel pump relay is located in the upper right side of the engine bay, behind the battery.
• Wear protective gloves and goggles when working with fuel.
• Check for common problems before moving on to the fuel pressure regulator, such as bad gas or a faulty fuel filter or pump.
• If you need to remove the vacuum line, check for fuel coming from the nipple. If there is, the regulator is faulty and needs to be replaced.
• Keep a rag handy when working with the Schrader valve to catch any escaping fuel.
• Keep the engine cold while working on the fuel system.
• Open the gas cap while the engine cools down to help relieve the vacuum in the system.
• Consult a mechanic or a detailed guide if you are unsure about any steps in the process.

Vacuum hose connection

The vacuum hose connection on the fuel pressure regulator of a 1990 W124 Mercedes 300E is important to understand, especially if you're performing maintenance or repairs on this component. Here's a detailed guide to help you with this specific aspect:

Location of the Vacuum Hose Connection

The vacuum hose connects to the rear of the intake manifold. It is part of the vacuum system, which influences fuel pressure regulation. This hose leads from the fuel pressure regulator to the intake manifold, creating a low-pressure area that draws fuel vapours into the air intake system rather than letting them escape into the engine bay.

Troubleshooting and Diagnosis

If you suspect an issue with the fuel pressure regulator, there are a few initial checks you can perform. Firstly, check for any unusual smells, such as a strong gasoline odour after driving. Additionally, if your car is stumbling or stuttering under acceleration, it could indicate a faulty fuel pressure regulator. However, before jumping to conclusions, it's important to rule out other common problems, such as bad gasoline, a clogged fuel filter, or a malfunctioning fuel pump.

Testing the Vacuum Hose Connection

One specific test you can perform involves removing the vacuum line from the fuel pressure regulator. If you notice fuel coming from the nipple, it confirms that the regulator is faulty and needs replacement. This test is crucial as it directly inspects the condition of the vacuum hose connection.

Safety Precautions

When working on the fuel system, it's essential to prioritise safety. Always work in a well-ventilated area, keep a fire extinguisher nearby, and avoid any sources of sparks or open flames, including smoking. Additionally, wear protective gear, such as gloves and goggles, whenever handling fuel or working on the fuel system.

Repair and Replacement

If you need to replace the fuel pressure regulator, it's a job that can be done in about an hour with the right tools and parts. You'll need a circlip tool and a flathead screwdriver. Remember to relieve the fuel system of pressure before starting any work. This can be done by removing the fuel pump relay, cranking the engine a few times, and opening the gas cap while the motor cools down. Always refer to vehicle-specific repair manuals and consult with qualified mechanics for more complex issues or if you're unsure about any procedures.

Fault diagnosis

There are several ways to diagnose a faulty fuel pressure regulator in your 1990 W124 Mercedes 300E. One common symptom is a car that stumbles or surges under acceleration. You may also experience changes in engine power and performance, such as a lack of acceleration when pressing the gas pedal or the car trying to stall.

Before assuming that the issue is with the fuel pressure regulator, it is important to rule out other potential causes. For example, you should check the quality of your fuel, the age of your fuel filter, and the functioning of your fuel pump.

One way to check the regulator is to remove the vacuum line. If there is fuel coming from the nipple when you pull off the vacuum connection, the regulator is faulty and needs to be replaced.

Another method to diagnose fuel-related problems is to perform a fuel pressure test. This will tell you whether the fuel pressure in your car is within the recommended range. For this test, you will need a fuel pressure gauge, such as the Actron CP7818 fuel tester. During the test, you will connect the fuel pressure tester to the fuel test port on the fuel rail and check the fuel pressure while the engine is running. If the pressure is outside the normal range, it could indicate a problem with the fuel pump or the fuel pressure regulator.

Additionally, you can perform a simple hearing test by turning the ignition to position II without starting the car. If you do not hear the fuel pump running for several seconds, it may indicate a problem with the fuel pump or the fuel pressure regulator.

If you suspect that the fuel pressure regulator is the culprit, it is recommended to have it inspected by a qualified mechanic or a Mercedes-Benz specialist to confirm the diagnosis and perform any necessary repairs or replacements.

Part sourcing

If you are looking to source a fuel pressure regulator for your 1990 W124 Mercedes 300E, there are a few options available to you.

Firstly, it is important to identify the specific part number for the fuel pressure regulator that fits your vehicle. According to Pelican Parts, the part number for the fuel pressure regulator for the 1990 Mercedes 300E 2.6, 300E 4Matic, and 300TE 4Matic Sedan is #000-078-03-92-M14. The part number for the 1990 300CE Coupe is #000-078-11-89-M14. It is important to verify that these part numbers are compatible with your specific vehicle before making a purchase.

Once you have identified the correct part number, you can source the fuel pressure regulator from various suppliers. Pelican Parts offers new fuel pressure regulators and provides free shipping for orders over $99. They also offer a lifetime replacement program. Another option is to check online marketplaces such as eBay, where you can find used fuel pressure regulators for the Mercedes W124 300E M103. These used options may be more affordable, but be sure to check the seller's feedback and return policy before making a purchase.

When sourcing parts for your vehicle, it is important to consider the condition, compatibility, and safety of the components. Always refer to a trusted mechanic or a professional automotive service for advice and guidance on part sourcing and installation.

Frequently asked questions