'82 SC Tach Jump and Sudden Radio Turned off......

Rodney Nelson · Rodney Nelson's Garage

On the way to work this morning I looked down at my tach and I was way way past readline, the only problem is that I was going 30 mph in 3rd gear !!!!!!! Then I got all mad and thought maybe it was my alternator, but then I noticed that the light was not on. I figured well I will just keep on driving to work, then a couple of blocks latter the radio shut off. That is when I did an immediate u-turn to go trade the 911 in for my Toyota Tundra (I knew that would run fine!). Well as soon as I turned around everything went back to normal and stayed that way all the way back home for about a mile and half.

Okay, so it has a brand new (2 month old bosch rebuilt) alternator in the car. I also just put in two new H4s (I did not install any additional relays) in the car about a month and half ago. As for my Stereo it has been in there for a couple of years, it has a high power amp and a high power deck.

I have had my Tach jump around before but the alternator light came on at the same time, but this time the alternator light did not come on so this is different?

Where should I start when I get home????

Graham Archer · 02-01-2006, 11:23 AM

You might want to check the connections at the battery. A loose connection can cause those symptoms.

Early_S_Man · 02-01-2006, 11:35 AM

Rodney,

It sounds like the regulator has failed in your alternator with integral regulator ... but it MAY have already done permanent damage to your tach or radio, too! BTW, the alternator warning lamp never coes on when the regulator is causing output Voltage to be way too high! The warning lamp only comes on when output Voltage is too low ...

What you need to know is what Voltage the alternator is putting out now, not the history of when it was most recently reolaced!

Get a multimeter, prepare a test cable to allow continuous monitoring of the 12 Volt accessory socket, and give us some data ... Voltage at idle, 2000 rpm, 3000 rpm, 4000 rpm, etc., or your best estimate of rpm, if you don't have a dwell-tach.

Rodney Nelson · Rodney Nelson's Garage

Great advice guys.

Okay so I will check the battery connectin when I get home.

Then, I will check the output voltage, it may be to high.

I will post my results later on tonight.

Thanks for your help,

mtelliott · 02-01-2006, 11:56 AM

Ground, ground, ground. Tranny ground and battery ground. It's cheap insurance. If they have never been replaced, it's time.

The alternator light might not come on if you are getting a voltage spike.

Michael

Rodney Nelson · Rodney Nelson's Garage

Mechael,

Crazy enough, I have actually replaced both of these, however, I will check to make sure they are still making good contact.

Thanks,

classic911 · 02-02-2006, 08:14 PM

Help-got into my 1982 911sc after shopping. Drive 50 yards and the alternator light goes on-sure enough I'm driving home and the radio dies, the lights get dimmer, car starts sputtering and dies-200 yards from my house!!!!

Where do I begin???

Early_S_Man · 02-02-2006, 09:11 PM

classic,

The next time an alternator warning lamp comes on, you might want to pull over and check to see if the fan belt is still in place ... very serious to drive without cooling air movement!!!

Pull the alternator, and get it tested at an alternator/motor repair shop.

Rodney Nelson · Rodney Nelson's Garage

Warren,

I have not had a chance to test the car yet but I will this weekend. I did check the connections to the battery and they are good.

I do have one question, why would the stereo turn off if there was a voltage spike? I could see if it blew a fuse, but a couple of seconds later it turned back on?

I also have a really nice snap-on battery, alternator, and starter tester. So I will see what that says this weekend too.

Classic911, good luck on that!!!!

Early_S_Man · 02-02-2006, 10:13 PM

Rodney,

It is my understanding that some late stereos have protection circuits that activate when the power input levels are out of norm ... and it sounds like yours worked as designed.

mtelliott · 02-03-2006, 07:29 AM

I concur with Warren. Most car stereo's have circuit protection built in.

I'm still wondering about what your initial problem might be. If you checked the connection at the battery and the connection at the transmission, it sure points to a bad alternator. You've probably already done this but test the voltage at the battery with the car running and someone reving the engine up and down. See how the voltage changes if at all. If you see spikes, then the alternator (voltage regulator) is most likely the issue.

Rodney Nelson · Rodney Nelson's Garage

Wow, I did not know they had voltage protection like that, you learn something everyday.

I will do a full check of the system on Saturday/Sunday. I am just so sick of this alternator thing. Seriously, this is like the 3rd one I have replaced, well the first two were rebuilt by a quality lacking shop. But the one I got in ther now was factory rebuilt....

However, I can change the Alternator out in like 2.5 Seconds if need be, I got that down to a science.

BlkBird · 02-03-2006, 07:59 AM

Have to agree with Warren. When my voltage regulator went sour it would spike to 18+ volts. The tach would go nuts and the radio would shut off (protection circuits).

Found out by attaching a digital multimeter to a wire under the dash and then went for a drive. When the tack went crazy I glanced at the meter sitting in the passenger seat. Bingo!

scottb · 02-03-2006, 10:20 AM

Quote:

Originally posted by Rodney Nelson
On the way to work this morning I looked down at my tach and I was way way past readline, the only problem is that I was going 30 mph in 3rd gear !!!!!!! Then I got all mad and thought maybe it was my alternator, but then I noticed that the light was not on. I figured well I will just keep on driving to work, then a couple of blocks latter the radio shut off.

I had similar symptoms (tach jumping and radio dying) when my alternator went bad. Even though yours is recently rebuilty, my guess is that something failed in it; possibly the regulator. Did you get a warranty with the unit?

Eric Coffey · 02-04-2006, 03:09 PM

Yep, sounds like a bad VR. Since it is usually intermittent, verifying the voltage (spike) can take some time. I found that using an old cell-phone car charger cord works well for real-time voltage monitoring. You just cut off the phone end, strip the leads and crimp on connectors to plug in to your DVOM. Then you can just plug the other end into the cig. lighter, and monitor the voltage from the driver's seat. If the stereo cuts out, and you see something like 17V on the meter, you have found the problem.