Alternator=Kaput?

[JCoop]

Since it almost hit a record-breaking 70 degrees yesterday, I drove all the toys. The CAV's battery seemed down when I cranked her up but started right up with a bit more sneezing and coughing from the Webers than usual. I noticed that the amp meter was a bit below 12V. Normally, when I rev it up, the needle jumps and then shows a charge of around 14V until it stabilizes. It stayed at around 11.5V for about an hour's drive. After I pulled back into the garage, I shut down and restarted her up and she did start again but the cranking was weak. I've put the charger on the battery overnight.
3800 miles on the 302; what should I check first? I'm a bit challenged when it comes to electrics...

Thanks!

 

[Larry]

Ray,
I'd start with grounds.
Larry

 

[Mort]

I doubt it is ground but good first step. Probably the built in voltage regulator in the Alternator is not working. May be moisture but have had this problem and in the end needed to change alternator.
The warm weather creates moisture in the garage despite what one thinks and this settles on eletrical connections.
Hope this helps!

 

[Bill Musarra]

Since most of us will let our cars sit for extended periods of time you may want to check into a battery tender. They aree marvelous little devices that will keep the battery up to charge for that once in a while get away. Check out one of many here or put battery tender in Google.

BatteryMinder Battery Tender Charger Auto

Bill

 

[Lynn Larsen]

Ditto what Bill M. said! All it took was one ruined expensive battery while my car was at the paintshop to convince me that the nominal cost of a battery tender was well worth the cost.

Doubt that is the problem here. After checking that wiring is sound, including the grounds, whose importance cannot be overstated, the voltage should never fall below 12v when the engine is running. Indeed, I would call it suspect if it fell below 13v except in momentary high draw situations or if you just have a grossly undersized alternator. If the alternator checks out on a test stand, you may need one with more output. BTW, EFI requires a lot of juice and can act very squirrely with marginal or inadequate power.

 

[JCoop]

Thanks guys. The battery's still good, held 13V after an overnite charge. However, needle goes to 11.5 after idling for 2 mins. and turning on A/C, fan, and headlights. So I guess I'll have to take the alternator out for a bench test. Amazing what a 3-week sit in the garage will do...

 

[CliffBeer]

Ray, I'd guess you have a poor ground. Check all the grounds you can find - checking means actually unbolting and cleaning as my experience has been that a fine looking ground can often be not making a good connection. Clean all the connections at the alternator as well. Clean the battery terminals. You might want to replace the main ground strap from the chassis to the engine - these can look OK but be a problem. They're cheap to replace.

If the above doesn't solve the problem then it's worth looking at the voltage regulator - will be internal to the alternator on most modern cars but can be external as well.

Persist and be diligent/careful and you'll find the problem.

 

[JCoop]

Well, finally got a chance to take the alternator out. The unit on the CAV is a Delco unit with an internal regulator, with special bracketry to fir it to the 302. It also does not have the fan installed; perhaps to clear the bracket and in anticipation of little usage. I'm sure this is the cause of the failure. Interestingly, there is a protective cap with mesh sides in the back, to protect against debris since it sits at the bottom of the motor. I brought the unit to Sailon Electric in Syosset (one of the last remaining motor/electrical specialty shops in Long Island) and settled on a 70 amp replacement unit, smaller, internally regulated, and with an internal fan. Works like a dream, should last the life of the motor.

Cheers!

 

[JCoop]

Sorry double post...