Possible bad Fuel pump or what!

sc · 10-28-2006, 08:39 PM

Had a strange experience today with my 1979 sc. Car started fine and drove it 15 minutes to my local Home Deopt. Whe I returned 20 minutes later it would turn over but not start.

- First thing I checked was if the engine was getting fuel. I left the ignition on and removed the air filter to manually move the air sensor plate. The plate had zero resistance and no fuel movement was heard.

- Next I checked the fuel pump relay. With the ignition on I removed the relay and could hear the contact opening and closing. Still no pump hum, so I bypassed the relay and jumpered pins 87a and 30 at the relay socket. Still no pump noise so I them jumpered pin 30 directly to a 20amp fuse and again no pump noise.

- So my thought was a bad fuel pump. Had the car towed home later in the day.

- At home I decide to retest. With the ignition on I re-installed the relay. This time I could hear the fuel pump hum. I checked the air sensor plate and had resistance and noise. I turned the key and she started.

So my question is, could it actually be a pump starting to go out or an electrical issue like a loose ground or connection. Seems pretty odd that the problem later corrected itself and the only change was it being about 6 hours later and a 15 minute tow home.
-sc

Boxer_Airhead · 10-28-2006, 09:55 PM

Do you have a fuel pump kill switch? If so, maybe the wires run under the driver's side carpet like mine. If that is the case, make sure the kill switch is working properly and check to see if your feet are messing with loose wiring.

Just my 2¢.

sc · 10-28-2006, 10:10 PM

Boxer,

Is this a factory switch?

Thanks
sc

Quote:

Originally posted by Boxer_Airhead
Do you have a fuel pump kill switch? If so, maybe the wires run under the driver's side carpet like mine. If that is the case, make sure the kill switch is working properly and check to see if your feet are messing with loose wiring.

Just my 2¢.

Boxer_Airhead · 10-28-2006, 11:30 PM

As far as I know this switch is aftermarket and it's probably different in each Porsche that has one. I recently got my '81 SC Euro and it has one installed, however the switch was removed by the previous owner in the process of troubleshooting a similar fuel/starting issue (problem was the fuel accumulator; hot start problem). So the wires are currently capped under my driver's seat. The switch was installed to help prevent a thief from driving the beloved car away, and sometimes the owner too.

Let me know if I can help you with more info. I need a good excuse to play around with mine anyways.

Cheers!