'79 911 SC Targa - Fuel Pump-how test

[skime219]

Symptoms: the car is not a daily driver. Out for an afternoon cruise, crossed a bridge-when leaving the bridge there was a small drop off-a thump and the car died. Would not restart with clutch release and would not restart after pulling to the side of the road. Towed to local import shop, the next morning the shop tech starts the car no problem and pulls it into the shop. The car starts each time tried that day at the shop. Fuel pump was inspected but is new (replaced by PO a year ago). The next day car is driven by the tech and still restarts after sitting. I pick up the car and pay the enormous bill of $47. 2 days later I crank the car and after it idles for the few minutes the car dies and will not start. I then notice that I do not hear the electric hum of the fuel pump before cranking. I also note that the engine did not fast idle when cranked. The engine is turning over good and even fires on a few cylinders when attempting to crank.

Potential cause?: Check fuel pump, what is the best test for that? Other suggestions?

[sylvester]

hi.. i have 79 sc coupe the samething happen to my car. check the little fuse in the trunk fuse box. i forgot which one it is. i think #6 or #7 thats mabe but sometimes it gets loose. if its not making a good connection the fuel pump wont work, theres also a fuel pump relay i think its red but most likely its the fuse good luck.

[skime219]

Something was tell me it may be a loose connection somewhere.
Will ck fuse as soon as I get home
Update--I checked records and the pump, relay and filter all replaced in 2003.
Keeping my fingers crossed on the fuse.

[Targalid]

You should not hear the "hum of the fuel pump" on turning the key. Rather, you hear the whine of the CD ignition module. The fuel pump does not activate until the motor begins turning on a 79. To hear the difference, take off your air cleaner turn on the ignition switch and push up on the air sensor arm. The fuel pump will come on when you do this. It is a totally different noise from the CD box. This makes me think you have an intermittent CD box problem, probably a loose connection since your narrative points to this.

[skime219]

When I pulled the fuse it felt loose, was for sure not very clean. Cleaned it up with some 200 grit, reinstalled-got a tight fit and turned the key. Heard the hum again...CD ignition module? or something and she fired right up.
Way cool.
This forum rocks, do hope one day I can be a solver instead of a question sender.
Thanks to both of you for the help.
D

[911freek]

I keep spare relays in the trunk, its a relatively cheap insurance and the darn things do fail. An 8 YO relay might as well be moody.