intermittent starting

[rubski82]

I have a 1984 pininfarina spider. It starts with once in a while. I can roll start it fine. When I jump it with another car it starts right up. If it does crank on its own it starts right up. When it won't start (most f the time) I just hear a humming. Output from the alternator while running is 14.2v at the battery 12.6v which i know is low. When the car is off I have 12.3v ish at the starter. Any ideas guys? Any other things I should test with my meter?

[azruss]

I vote for the starter solenoid. sounds like the internal contacts are dirty. The next time it won't start, have someone turn the key to the start position and give the starter a good bang with a 2x4 or shovel handle or something like that.

[RRoller123]

Also, check C17 and C31

[spider2081]

While the key is in the start position measure the voltage at the battery terminal of the starter solenoid then measure the voltage on the small spade terminal of the starter solenoid They both should be close to 12 volts. If either is less than 11 volts check connections at battery and at starter solenoid. On my 81 there is a single bullet connector near the driver side engine mount that could cause this problem. Also the C17 and C31 as previously mentioned. C17 is in the feed wire to the ignition switch usually located under dash near hood release. It is a 4 socket connector with brown and black wires in it. C31 is about 6 inches behind ignition switch.

[rubski82]

You guys are awesome. I'll check all those and hopefully have success. Thanks

[bpadda]

Hello Rubski82, I know this is a old thread but did you ever confirm what the exact reason for the no start humming was?