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How to Check the Fuel Pressure on a Mercedes Benz

Post Date: 16th February 2018


Dedicated Mercedes Benz owners will perform frequent checks on their vehicles on a monthly basis, ensuring that everything is working smoothly – from the sound of the engine to the thickness of tyre treads. Looking after your car is well worthwhile to ensure it has a long lifespan, and as an owner you can have peace of mind by knowing your car is safe to drive.

If your Mercedes Benz has started developing persistent issues with the engine or the engine light has come on, it could be related to a wide range of issues. To diagnose the issue (and to rule out fuel pressure) it’s a good idea to check the fuel pressure of your car as soon as you can. Below we have outlined how simple it is to perform and how you can do it at home before taking it in to see a mechanic.

What you will need to perform a Fuel Pressure Test

Performing a fuel pressure check is reasonably simple as you only need one piece of equipment, though it is wise to take every available safety measure so that the check is as easy and accurate as possible. The following items will be necessary to perform the check:

A Fuel Pressure Tester

Thin Gloves

Small Plastic Dish (to catch excess fuel)

Old Rags or Kitchen Roll (to catch excess fuel or clean it off afterwards)

Small Fire Extinguisher (for any emergencies involving fuel leakage or otherwise)

Steps to Performing a Fuel Pressure Check

 1. Make sure engine is off and has cooled down

The first step is fairly obvious, but when checking the fuel pressure it is incredibly dangerous for the car to be either on, or for the engine to still be hot. This can easily cause a fire in the engine so it’s best to leave your car for at least an hour or so after driving and then ensure that the engine is completely cold before you perform the check.

2. Open the bonnet and remove engine cover

Depending on the classification of your Mercedes Benz, you will have an easier or harder time removing the engine cover. Generally, it’s worth being aware that there will be a front cover and a back cover, with the front cover being the easiest to remove. This will pop out by firmly pulling up on the front, whilst the back cover will require you to disconnect the flex intake hose and breather hose before removing the cover itself. If in doubt, always check the owner’s manual for the correct procedure.

3. Locate the fuel port

Once you have the engine cover removed, you should have a better view of the engine itself. The fuel port should be located at the end of the fuel line that runs from the fuel injectors. These may be positioned slightly differently depending on the model of the car, if you’re unsure check the owner’s manual for clarification.

4. Remove the Schrader valve cap

Once you’ve located the fuel port, remove the cap covering the schrader valve. Ensure you are ready with your plastic dish or with old rags in case any excess fuel comes out. Seeing as your engine will be completely cold, you can simply wipe up any excess fuel.

5. Connect the fuel pressure tester

The fuel pressure tester will be able to be attached to the Schrader valve fairly easily by screwing it on. Make sure it is firmly attached before moving on. Have the pressure gauge facing up so you can make an accurate reading once you turn the engine on.

6. Turn the ignition on

With the pressure tester attached, turn the ignition on. Since the pressure tester will be attached firmly there should be no fuel leakage but you should still keep extra safe by having your fire extinguisher close by.

7. Check the fuel pressure reading

You should now be able to check the fuel pressure reading on the visible gauge. This should be between 50 and 55 psi when the car is idle. When revving the engine it should increase by around 2 psi. However, check the owner’s manual to confirm what should be standard for your vehicle as it can vary depending on the model of your Mercedes.

What do the results mean?

Any reading that is higher or lower than the standard psi means your car may have an issue. Low pressure is the most common problem, and this can be caused by a faulty fuel pump, a fuel leak or a clogged fuel filter. High pressure means you may have a clogged return line or a bad fuel regulator. Either way, it is worth bringing your vehicle in for a service to confirm and fix the problem.

To book in a service for your Mercedes Benz at Dronsfields, visit our Repair/Service page and fill out the form. For any other enquiries, get in touch with our expert team today.

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