- Park the Porsche on a level surface and set the parking brakes. Allow the engine to cool down.
- Next, you will need to access the engine. Pull the hood release under the dashboard to open the hood.
- Remove the engine cover.
- Locate the fuel rail. At the end of the fuel rail, you will find the test port. Most Porsches use what is known as a Schrader valve. Place a rag under the fuel port to catch fuel leaks. Remove the cap and connect your gauge.
- Start the car to measure the fuel pressure with the engine running. Check the pressure with the engine running at 2000 RPM, 3000 RPM. Check fuel pressure at idle.
At idle, fuel pressure should be in the 45 to 55 PSI.
At 2000 or 3000 RPM, the pressure should be around 50-55 PSI.
If your Porsche is struggling to start, you may want to check the pressure after turning off the engine. Keep the gauge connected for at least fifteen minutes after you shut off the engine. The pressure should stay constant. If you are losing fuel pressure too quickly, you may have leaky fuel injectors or a fuel leak. Another issue could be a bad fuel regulator.
If your Porsche starts but then it stalls, the primary fuel pump could still be the problem. On Porsches that have two fuel pumps, the secondary pump primes the system at startup, and the engine starts. A few seconds later, the engine dies. A bad primary pump will cause the engine to stall or run rough after startup.
Just like low fuel pressure, extremely high fuel pressure such as over 100 PSI can be a problem and can cause the engine to run rough.