bouncey tach.

[CindyDuck]

The tach in my 79SC intermitently goes wild. I switched it out with a tach from a 77S and still the same problem. I have searched the shop manuals and can nothing on trouble shooting such a problem. Any sugestions?
Thanks,
Mike

[Jess]

Mike

Check the your charging system. I suspect that your voltage regulator isn't doing its job anymore. Use a voltmeter at the battery and see what the voltage there is with the car running. Rev the engine and if you see voltage much above 13.5, that's your problem.

Do you smell a strange smell in your car? It's probably your battery boiling.

Good luck,

Jess

[stomachmonkey]

I've got a similar intermittent issue.

Doing searches I came up with 2 front runners for the problem.

Alternator going south or bad ground somewhere.

I'd be happy to hear some sage advice from those that know.

Scott

[FrayAdjacent911]

Mine sure flutters a lot. I need to check the voltages when I do the tune up in a couple weeks. I hope it's just a regulator. Those are a lot less expensive and easy to replace!

[delaneyd]

I had the same problem with my 83SC. I replaced the battery with a red top Optima and the problem never came back. Watch to see if your headlights get brighter/dimmer when night driving--if so then it is probably your alt. ( I believe the voltage regulator is built in your alternator )

[CindyDuck]

I bet your right, the reg is going bad. I noticed it driving the other night, brighter with higher R's. It is located in the back by the CDI. Is 79SC the same as 77S? they look the same.
Thanks,
Mike

[afterburn 549]

if you have pts. that are old,,might cause this (did mine)

[Sonic dB]

I replaced my battery, replaced the alternator and voltage regulator and the thing still bounces the same.

maybe its just the tack

[CindyDuck]

OK, I replaced the regulator with the one off my 77 parts car and it worked. I had a surge as high as 14.6 at 3500 now I hit 12.7.
Thanks again guys, service manuals help alot but nothing beats experiance.

Mike

[Jess]

Mike,

I'm glad that was it!

You might want to remove your battery and clean up the area around it with some baking soda and water. If this has been going on for some time there's a good chance that the battery has been outgassing corrosive stuff that you don't want sitting in the trunk of your car.

Jess

[bigchillcar]

if you've eliminated your charging system components, the two next most likely suspects are your ingnition points (if you have them, this is always a first clue that they're going south) or a coil problem.
ryan

[Gunter]

Bosch CDI module for '77 has 3 connections; '78 and up has 6. They are not the same. '77 has points, '78-'83 SC's don't. Glad you found the problem.