1966 Dies after driving 45 minutes

[Sammy66]

Hello T-Bird Gurus!

1966 w/ 428

This just happened tonight, and I'll start digging into it this morning, but here's the scenario.

Out for a cruise tonight. Starts fine (finicky ignition switch though....but maybe not based on what happened).

Drive for about 45 minutes and then shut it off. 15 minutes later, try to start and nothing....no click, grunt, spin, nothing. Lights work, so I have at least some juice. Now I haven't had the issue of the column/shifter not engaging the safety switch, so I think I can safely rule that one out. After a 10-15 min wait, I try cranking again and can hear the starter make a small whine.....

I've had this happen before, but chalked it up to a low battery from lack of driving....charged 'er up and things were good. that said...this isn't a daily driver.

I jump started it again and off I went, but after about 10 minutes, the lights start to go dim and then poof.....engine dies. I've obviously just been running off the battery and she finally gave up.

So...now the question is, where should I start in the diag? I can put the battery on the Noco charger and get it back up to speed, but now I wonder....have I got a starter that's failed and is drawing so much it's killing the system? Have I got a bad alternator and have simply been living on borrowed time? Voltage Regulator? Flux Capacitor? Is the battery good or has it bit the green weenie as well?

Inquiring minds (me) want to know where you'd start oh wise ones.

My thanks in advance for your assistance.

 

[74 Harley]

Start by checking the running voltage, if it checks good do a load test on the battery.

 

[doug7740]

The charging system consists of the battery and cables, the alternator and voltage regulator. The function of the battery is to spin the starter motor to start the engine. Once that’s done, the alternator takes over, satisfying the car’s electrical demands and keeping the battery charged. The battery then acts primarily as a filter, keeping voltage spikes from damaging the car’s electronics. The voltage regulator rapidly switches the alternator in and out of the charging circuit to provide the car with the correct voltage.

On the 12 volt system there are two important numbers to remember, they are 12.6 volts and 13.5 volts. 12.6 Volts: If you think your car has a 12 volt battery, it doesn’t. The 12 volt battery actually has six individual 2.1 volt cells, and when fully charged, the battery should have a resting voltage of 12.6 volts. If with the engine off, the resting voltage is less than 12.6 volts, the battery is low and needs to be recharged. Of course, it begs the question of why the battery is low. It could be that the alternator isn’t working, or that the battery has reached the end of its useful life. 13.5 Volts: With the engine running, the alternator should output a charging voltage that’s about a volt higher than the resting voltage, or about 13.5 volts. The exact charging voltage may be as low as 13.2 volts or as high as 14.2 volts.

Take a multi-meter and set it to measure DC voltage, then measure the voltage across the positive and negative battery terminals with the engine off. On a 12 volt system, a fully charged battery should read a resting voltage of 12.6 volts. After you start the car you should see a charging voltage of about a volt higher than resting voltage. If the reading doesn’t increase by about a volt or if it stays at the resting voltage, it means that the alternator isn’t recharging the battery. This could be because the alternator is defective, the regulator is defective, or the wiring between them has failed. If the battery runs down enough that the ignition stops firing, the engine will stall. It’s really important that you don’t simply jump-start a car with a dead battery without checking to see if the alternator is charging.

A basic charging system health test: Use a multi-meter to measure the resting and charging voltages as described above. Then, with the engine running, gradually increase the electrical load by turning on the headlights and the blower fan. Then increase the engine RPM to about 3500 as you watch the reading on the multi-meter. If the voltage stays about a volt higher than resting voltage, then the car’s charging system is functioning. But if the voltage drops or increases dramatically at any point, there’s a problem with the alternator or the voltage regulator.

doug7740
1955 Thunderbird Blue

 

[Frankie the Fink]

I can tell you I had the same problem on my '61 Corvette, after having a 'no start' condition 1 out of every 5 times and it was a bad connection on the back of the ignition switch. So, when you describe your ignition as "finicky" that is a clue to me. Start with a solid physical inspection of all wires/cables/connectors looking for broken, frayed or loose wires.

 

[Sammy66]

The charging system consists of the battery and cables, the alternator and voltage regulator. The function of the battery is to spin the starter motor to start the engine. Once that’s done, the alternator takes over, satisfying the car’s electrical demands and keeping the battery charged. The battery then acts primarily as a filter, keeping voltage spikes from damaging the car’s electronics. The voltage regulator rapidly switches the alternator in and out of the charging circuit to provide the car with the correct voltage.

On the 12 volt system there are two important numbers to remember, they are 12.6 volts and 13.5 volts. 12.6 Volts: If you think your car has a 12 volt battery, it doesn’t. The 12 volt battery actually has six individual 2.1 volt cells, and when fully charged, the battery should have a resting voltage of 12.6 volts. If with the engine off, the resting voltage is less than 12.6 volts, the battery is low and needs to be recharged. Of course, it begs the question of why the battery is low. It could be that the alternator isn’t working, or that the battery has reached the end of its useful life. 13.5 Volts: With the engine running, the alternator should output a charging voltage that’s about a volt higher than the resting voltage, or about 13.5 volts. The exact charging voltage may be as low as 13.2 volts or as high as 14.2 volts.

Take a multi-meter and set it to measure DC voltage, then measure the voltage across the positive and negative battery terminals with the engine off. On a 12 volt system, a fully charged battery should read a resting voltage of 12.6 volts. After you start the car you should see a charging voltage of about a volt higher than resting voltage. If the reading doesn’t increase by about a volt or if it stays at the resting voltage, it means that the alternator isn’t recharging the battery. This could be because the alternator is defective, the regulator is defective, or the wiring between them has failed. If the battery runs down enough that the ignition stops firing, the engine will stall. It’s really important that you don’t simply jump-start a car with a dead battery without checking to see if the alternator is charging.

A basic charging system health test: Use a multi-meter to measure the resting and charging voltages as described above. Then, with the engine running, gradually increase the electrical load by turning on the headlights and the blower fan. Then increase the engine RPM to about 3500 as you watch the reading on the multi-meter. If the voltage stays about a volt higher than resting voltage, then the car’s charging system is functioning. But if the voltage drops or increases dramatically at any point, there’s a problem with the alternator or the voltage regulator.

doug7740
1955 Thunderbird Blue

Thanks for the fantastic advice! Rolling up my sleeves and checking everything today. First check....connections. I'll make sure I don't have any loose ones 🙂

 

[Sammy66]

So here's my testing results:

Charged battery - 12.5V

Running, no accessories on, reads about the same, with a slight increase to 13V.

Headlights on, drop to under 12.5V. Increase of RPM shows no increase, in fact it even dropped for a bit, and then back up to no more than 13V. Add the blower motor to the headlights and we're in the 12.2-12.3 range.

My experience tells me alternator....buuuuut, I wonder about the Voltage Regulator. My online sleuthing tells me they are pretty common to go bad (some bad right out of the box), so I'm guessing that could be a reasonable issue.

These readings tell me why it died on the way home....battery on it's own couldn't support the voltage required.

So....off to find a way to test the regulator.

 

[74 Harley]

Better to pull the generator and have it tested. It's free at your local parts store.

 

[Frankie the Fink]

I would think its an alternator in a '66 but yeah, methinks those voltages are low.

 

[Sammy66]

It is an alternator.