C4in mesa

Since I rebuilt the motor and have an underdrive pulley set (3) I have had odd electrical issues. My headlights will not turn on or they will be open and the bulbs will shut off for several miles before coming back on. My radio the same thing. When I am at idle the gauge reads 11.4 volts and when I am driving the gauge reads 13-14v so this tends to make me guess if the lack of proper voltage can be the cause ? No other system is affected that I have noticed. I think the headlights draw a far amount of juice which may be why ? Days might go by without having this happen and then other days it will happen more than once. There is no pattern at all.

The Plastic Lizard

Your system is running off battery. When it drops below 12 volts, weird things happen.

Your alternator can't keep up with the system. You should be over 12.5 volts at idle.

The intermittency is just due to how long your battery is able to hold a charge over 12. Need to boost the alternator via different alternator or increase the rotation by changing the pully.

C4in mesa

Let me correct myself. My idle is 11.9-12.4 but never anymore. When I start the car it is 11.4 or pretty close. I should have caught that error but I didn't proof read it. Still I am walking the line on proper voltage which is what I suspected to be the cause for the odd electrical problem. I have to ask before I start looking for a different alternator. Can I buy a alternator that produces more power than a stock alternator ? A slight more juice would possibly make up the difference. I don't know what specs to look for so I buy the right one. I hate to change the pulley but I know it would fix the problem.

WW7

On my 89 I have never seen the voltage gauge go below 13.6, and it usuallly reads between 13.8 and 14.1 at hot idle ... It seems your system isn't putting out enough voltage, whether it's the underdrive pulleys, or a bad alternator , I don't know..You can always pull the alternator and have it checked.......WW

383vett

Swap back to the original pulley and see if the problem still exists.

Klondike

I had problems with a "set" of underdrive pulleys and eventually put the stock pulley back on the alternator to speed it up a little and kept only the smaller crank pulley from the set. Changing the pulleys lessens the drag on the crank. If you put a bigger (more powerful) alternator on to make up for the voltage loss from spinning the stock one too slow, you will only just increase the drag again with the larger alternator. That just defeats the purpose of putting the larger pulley on the original alt in the first place. Then you will have spent (wasted) money on another alternator too. Keep the smaller crank pulley and put the stock pulley back on the alternator to spin it a little faster. With the smaller crank pulley you will still be turning everything slower than before but you won't be spinning the alternator TOO slow at low speed and idle like you are now with both pulleys slowing it down. Just get a little shorter belt to make up for the length difference with both a smaller crank AND smaller original alternator pulley. You'll get the best of both worlds and seat of the pants push turning everything a little slower but without your alternator running too slow.