fuel issues

mix77WB · 01-29-2025, 12:13 PM

Hello, I'm new here and new with owning a Porsche. I have a 1977 911 Targa that was turned into a wide body cabriolet with a 1987 fuel injected 3.2 engine. I was given this car from a friend, and it has been sitting in a garage for the past 5-10 years. I'm having an issue with the fuel system. The fuel pump constantly runs with the key in the on position and the cylinders are filling with gas causing a hydro lock on the engine. Not all cylinders are filling up. I'm getting the fuel injectors rebuilt. I'm just trying to figure out why the fuel pump is constantly running when the car is not. Thanks for any help.

ErrorMargin · ErrorMargin's Garage

The car may have just been wired to run the fuel pump all the time with the ignition on...but even if that is the case it would not cause the injectors to run and fill your cylinders with fuel without the engine running.

If you still have the injectors in the car, I would disconnect all of them from the wiring harness and then turn the ignition on. With the injectors disconnected from the wiring harness, they should not spray any fuel into the cylinders. If they spray fuel into the cylinder with the harness disconnected then the injector itself is leaking.

Rodsrsr · Rodsrsr's Garage

Agree with the above. Someone wired it that way when they swapped the 3.2 into the 77 chassis. I experienced a similar wiring situation with my 76 which led me to rewire the DME connector pins back to factory. As stated, fuel should not get past the injectors even if the pump is on all the time, it should just recycle back to the tank through the return line.

mix77WB · 12:23 PM

OK I confirmed that its not the injectors. I disconnected the main plug at the back of the motor for the injector wires and no hydro lock engine will crank until the battery dies. When I re connect that harness and try to start the car it only takes a few revolutions before it hydro locks again. I did notice there is a jumper wire on the fuse panel that goes from the fuel pump fuse #3 to fuse #8 (backup light, emergency flasher relay, and rear turn signal lights). I'm stumped? Any help is greatly appreciated. I have seen some other post that say the DME fires all of the injectors at the same time, not sure if that's true?

Rodsrsr · Rodsrsr's Garage

So your saying you disconnected power to the injectors and its fine but when you reconnect it hydro-locks? Sounds like an injector or injectors are indeed the problem and possibly stuck open.

After sitting for 10 years those injectors will definitely need servicing. I would also remove that jumper wire and see if it acts the same. If so, the fuel pump is working properly and someone probably jumped it to test but never removed it. Next steps would be to have the injectors serviced.

mix77WB · 05:24 PM

The injectors are new. it seems like the injectors are opening as if its at full throttle. I can run the fuel pump and crank the engine all day long with the injector wires disconnected but as soon as i connect them I get four or so revolutions out of the engine before it hydro locks on gas. It's driving me crazy lol.