If you have a car that's been sitting for an extended period with old gas in it, or if it simply has high mileage, some of your fuel system components may be clogged with an excess of contaminants and debris. In this guide, I show you how to refresh/replace the fuel system components on your air-cooled Porsche.
Like most cars, if your air-cooled Porsche 911 has been stored with gas in the tank for an extended period, it may go bad and start to gum up some of your fuel system components. This could cause hard starting, rough running conditions, or make your fuel gauge unresponsive. Even if the car has been driven regularly, high mileage will start to take its toll and slowly, causing similar symptoms. Replace your fuel filtration components and fuel level sensor with these simple procedures and restore the original function of your 911’s fuel system.
Model Years Applicable:
This DIY applies to all Porsche 911 models up to 1989. Note, however, that fuel filters changed several times over the years, so make sure you select the correct one for your car. If your car has very old gas in the tank that smells bad, you should drain the tank completely; this way you don’t contaminate your new fuel system components as soon as you attempt to start the car again.
General Tools Needed To Complete This Repair:
- Metric flare nut wrench set
- Rags for fuel spill cleanup
- Drain Pan or Bucket
- Hand transfer pump (for draining fuel)
- Rubber/Nitrile gloves
- Safety glasses
- Fire extinguisher
- Penetrating oil
Tools Needed For Fuel Tank Screen Replacement:
Parts Needed To Complete This Repair:
- Fuel filter (varies per year)
- Fuel filter sealing rings (varies per year)
- Tank screen (1974-89 only)
- Tank screen seal (1974-89 only)
- Tank level sensor
- Tank level sensor gasket
Fuel System Precautions:
- Disconnect the negative battery terminal.
- Keep a fire extinguisher nearby for each of these procedures.
- Work in a well-ventilated area with no sources of heat, spark, or open flame.
- Make sure the fuel tank has as little fuel as possible to reduce the chance of gasoline spillage.
- Work with as much ambient and overhead lighting as possible to keep electric work lamps away from fuel vapors.
- Gasoline is carcinogenic so wear rubber gloves, long sleeves, and safety glasses to protect your skin.
Fuel Filter Replacement Procedure:
Step 1: Release Fuel Pressure
First, start by locating the fuel filter. In most 911s it will be in the engine compartment, above the engine on the left side. Spray a little penetrating oil on the fuel filter fittings to make removal easier. If the engine has run that day, let the car sit overnight to let some of the fuel pressure release within the system so the engine can cool down.
The next day, with a rag in hand to catch any fuel that might spill, loosen the upper and lower fuel filter fittings. If there is any residual pressure left in the lines, a small amount of fuel may spray out momentarily.
Step 2: Remove Filter
If you have a 911 SC, the fuel accumulator is right next to the filter, joined with an S-shaped hard fuel line. It may be easier to disconnect the upper fitting on the filter, one upper and lower fitting on the accumulator, and pull the whole assembly out so you can replace the filter on the bench.
Some early cars (with mechanical fuel injection) may have a fuel filter element located under a hard-plumbed filter mount, appearing similar to a very small spin-on oil filter. In this case, disconnect the lower hose and loosen the filter by spinning it off the upper filter mount. Early cars with carburetors have a small can filter with hose clamps securing the fuel lines. Loosen the hose clamps and pull the fuel lines off.
Remove the filter from the car and take it to a bench. Examine it next to your new replacement filter. Compare the filter connections; if your new filter comes with new threaded fittings to connect it to your fuel lines, use those. Otherwise move any missing fittings from the old filter onto the new filter, along with new sealing rings to prevent fuel leaks. Tighten the fittings onto the new filter while you have it on the bench.
Step 3: Re-install Filter
Carefully re-install the new filter onto the fuel lines making sure you use new sealing rings. Thread the fuel line fittings and tighten as far as you can with your fingers. Finish tightening each fitting with a wrench, holding the filter fitting still and turning the fuel line fitting to tighten.
On early mechanical fuel injection cars, spin on the filter and tighten as much as possible by hand. Much like an oil filter, a rubber sealing ring will seal against the filter mount surface. If necessary, snug it a bit further using the hex fitting on the bottom of the filter. Reconnect the lower fuel line as it was originally connected. On early cars with carburetors, simply push the fuel lines back onto the new filter and tighten the hose clamps to secure them.
Step 4: Pressurize Fuel System and Check for Leaks
With a fire extinguisher and rags nearby, turn the ignition key to the “on” position to start the fuel pump and pressurize the system. Check for leaks around the filter and engine compartment. Once you have confirmed there are no leaks, start the car and let it run for a few minutes to confirm no leaks are present. The car may take a few extra cranks to start since it needs to purge the air out of the fuel lines and the new filter.
If you have a very early car with a mechanical fuel pump, you will have to start the car to check for fuel leaks around the filter. As before, keep an extinguisher nearby just in case.
Fuel Level Sensor Replacement Procedure:
Step 1: Empty Front Trunk and Locate Sensor
Open the front trunk and empty it out. If you have trunk carpet, remove it to expose the bare fuel tank. Find the electrical connection for the fuel level sensor on top of the tank.
Step 2: Remove Sensor
Remove the bracket holding the sensor electrical plug in place. Save the nuts and washers for reuse later.
Gently pull off the plug to expose the top of the fuel level sensor.
Remove the remaining nuts and washers from the top of the sensor and set them aside. Using a plastic trim removal tool, gently pry all around the sensor flange. Once it begins to lift, grab a rag and get ready for a small amount of fuel to leak out from around the sensor tube.
Slowly lift the sensor all the way out and let the end momentarily sit over the opening of the tank to allow any fuel in the sensor to drain back into the tank. Wipe up any spilled fuel.
Step 3: Remove Gasket and Inspect Tank
Wipe the sensor dry and set it aside. If the rubber gasket is stuck to the tank opening, carefully peel it off with the plastic trim tool, taking care not to drop any pieces of gasket into the tank. This is a good time to peer into the tank with a flashlight and get a good view of its interior the inside. It should be nice and clean with no debris at the bottom. Any gas left in the tank should be clear.
If your tank interior is very dirty or worse, rusty, you may need to consider draining the tank, removing it, and either taking it to a specialist for professional cleaning or replacing it with a new one. Any contaminants in the tank will quickly clog up your fuel system once again.
Note: If you will be replacing the fuel tank screen next and you still have gas in the tank, it's recommended you drain the tank now through the tank opening using a hand-transfer or siphon pump.
Step 4: Reinstall New Sensor and Gasket
If your tank interior is clean, you may now place a new gasket onto the tank opening and insert a new fuel level sensor into the opening. Install the electrical plug, bracket, washers, and nuts. The nuts are tiny, so they should be hand tightened to just snug in a star pattern. Also, do not re-use your old gasket as it may cause fuel vapor leaks.
Turn the key to the "on" position, and the fuel gauge needle should now flip to life.
Fuel Tank Screen Replacement Procedure:
Note: The fuel tank screen is essentially a large fuel tank drain plug. This procedure will drain your tank very quickly. It is highly recommended you start with an empty tank to prevent dangerous fuel spills; otherwise, you will need to drain it by disconnecting the fuel pump inlet line under the tank as described in steps one through four in this procedure and collect the fuel in a bucket. Another way is through the fuel level sensor opening at the top of the tank using a fluid transfer pump as described in steps one through three in the preceding procedure.
Step 1: Raise the Car on Jack Stands
Raise the car on jack stands using this procedure. We will be working on the bottom of the tank and will need room to put a bucket under the car to drain any remaining gas.
Step 2: Locate the Tank Screen Plug & Remove
Under the tank, look for the large hex plug; it should be straightforward to spot. Place a bucket under the hex plug to catch any remaining gas in the tank.
Use a 22mm hex bit to loosen the plug. If you don't have a hex bit that large, in a pinch you can use a spark plug socket with a 13/16” external hex. Insert the hex end into the tank plug and insert a ratchet extension from the opposite side of the spark plug socket to turn it. A third option is making a tool with a large bolt with a 22mm hex head, and two nuts tightened against each other on the bolt threads.
Break the plug loose and slowly turn until gas starts to drip out. Turn the plug until gas drains out at a controlled rate into the bucket. There are very few threads on the plug, so it may just come out completely with gas rushing out at full speed. Once the gas is fully drained, immediately transfer it to a closed fuel container. If the plug sealing ring is stuck to the tank opening, remove it.
Step 3: Replace Tank Screen Plug and Seal
Place a new plug seal over the new tank screen plug and thread back into the bottom of the tank by hand. Torque to 25 N-m (18 lb-ft).
That's it, the whole job is complete, and your fuel system is now ready to provide you a correct fuel gauge reading and maximum fuel flow for years to come. If you find this guide useful or are just enjoying following along, make sure to check back here often and subscribe to our YouTube channel for more.
Having explored the fields of aerospace, power generation, automotive aftermarket, and concept car engineering, I'm now a development engineer for Mazda North America. In my spare time, you can find me wrenching on anything, but mainly cars of the air-cooled variety. @joe_engineer