Intermittent Starting Problem with 79 911SC Engine

73ess · 01-21-2016, 01:49 PM

Experiencing an intermittent starting problem with a 73 with 79 3.0 SC engine in it. Brand new battery installed and battery terminals clean and tight. Car started up after new battery install. I then shut it down and tried restarting, but just hearing a click back where the starter is. After click I can see all power go out (e.g. radio face goes dead). Then I reconnect battery terminal and power comes back, then turn key and only get a click and lose power again. I think a loose connection somewhere. Will check cables back at starter. Anywhere else I should be checking?

Porsche 2 · 01-21-2016, 02:42 PM

Check/clean tranny to body ground strap, located under tranny near tunnel.

pete3799 · pete3799's Garage

Could also be the ign. switch but check and clean the ground mentioned above first.

73ess · 01-21-2016, 04:18 PM

Thanks guys. Will check ground strap first, then connections at the ignition switch.

73ess · 01-22-2016, 08:11 AM

I forgot to mention that when the car was last running, it shut down completely while idling at a stoplight. Turned key, nothing. Had my wife behind me so attached jumper cables from her running car and it then started up fine. I'll definitely check that tranny to body ground strap first.

wwest · wwest's Garage

Quote:

Originally Posted by 73ess

I forgot to mention that when the car was last running, it shut down completely while idling at a stoplight. Turned key, nothing. Had my wife behind me so attached jumper cables from her running car and it then started up fine. I'll definitely check that tranny to body ground strap first.

Intermittent internal battery connection.

When it depowers tap the battery posts lightly.

Targalid · 01-22-2016, 09:15 AM

The click you hear when you turn the ignition switch is likely the starter solenoid. You turn the key and the solenoid is energized. The solenoid should then switch power from the big positive wire, at the starter, through the starter motor and whirrrr, rumble. That you release the key, which should interrupt power to the solenoid, and your power is gone system wide, suggests that something is sticking, either in the ignition switch or the starter assembly. Your last post indicates that your battery is being very quickly drained. Have you checked the voltage at the battery terminals of your new battery when this happens?

LM3929 · 01-22-2016, 11:02 AM

if you have an original braded ground cable replace it with one from pelican.

I had the same problem, replaced the electrical portion of the ign switch and it was the same problem.

it was my poor ground wire and possible paint on the body.

lorne m.

gomezoneill · gomezoneill's Garage

I've seen many batteries crap out new check the voltage at the battery.

73ess · 01-22-2016, 12:58 PM

Just ran a continuity test between the ground at the battery and the transmission case. Test passed with flying colors. No resistance. So I'm assuming the ground strap up the transmission case is fine?

Avanti · 07:03 PM

Continuity test is not accurate to test braided or strand wire cables. You have to do a voltage drop test. Connect the multimeter leads the same way and put the multimeter on low volts like under 20 if not using an auto ranging meter. While holding the leads firmly in place to have good contact have a helper crank the engine over. A starter circuit on an old car like ours should have no more than a .5 voltage drop reading. The voltage reading you get is the amount of voltage that is lost due to resistance in the circuit/wire you are testing.

heathm · heathm's Garage

I had a similar problem on my C3.
The issue was the negative strap to the body at the body end from the battery. It had loosened as i was moving the battery around on installation. Definitely pays to clean and check the body connections

73ess · 01-23-2016, 09:24 AM

What electrical problem would cause the engine to die while idling? Battery disconnect wouldn't as it would still run with alternator running. I guess if fuel pump lost power?

How do I go about jumping the starter? Jump the yellow wire directly to the larger stud at the starter and then connect battery? Of course with trans in neutral.

73ess · 02-03-2016, 10:11 PM

Well I switched out the ignition switch with a known good used one and voila, the starter worked fine and engine started up fine. Then drove it for a few blocks, got to a stop sign, heard some gurgling sound from I think the fuel pump up front and the engine died. Restarted fine, but died again after gurgling sound. Parked it in my garage overnight with battery disconnected. This morning went to start the car after connecting battery. Nothing, nada, zilch. Lights work fine, but I turn keyswitch and get nothing. Not even a click. What the heck?

Targalid · 02-04-2016, 06:17 AM

Check your battery voltage when the car dies. I bet it is below 11 volts. Why? It is not being charged. Why? That is your mission: to find out. But first, get a diagnosis: check the battery to see if it is dead. Or... you can replace more parts and then check the battery voltage.

73ess · 02-04-2016, 07:08 AM

Battery voltage is fine. 12.84 V. Just bought a brand new ignition switch so I'll see if that works first.

Targalid · 02-04-2016, 07:55 AM

The battery is not dead but the entire electrical system is dead when it stops running. No headlights? This limits the problem to between the battery and the fuse panel since the headlights run without the ignition switch. If you have headlights then look to the 14 pin connector in the engine compartment. You may have oxidized connections there. Try disconnecting and reconnecting several times, after brushing the pins lightly with a wire brush or abrasive pad. My engine died like yours is doing, caused by oxidized 14 pin connector.