When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
1968 Cutlass S Convertible possible alternator issue
When driving the car sometimes, especially when are a stop light or in a drive thru, randomly when the idle is low, the gen light comes on, makes a buzzing sound and then the car will cut off unless you gas it. No issues starting it back up... But sometimes an issue getting it to stay running with it low idle before you can get it back into drive.
If it is a 2-bbl carb (not sure if the 4bbls have this), check the wiring to the idle solenoid. If its loose, the solenoid will retract and allow the throttle plates to close a bit more, slowing the idle speed to the point of nearly stalling. If that's not it, check your carb's idle settings.
If it is a 2-bbl carb (not sure if the 4bbls have this), check the wiring to the idle solenoid. If its loose, the solenoid will retract and allow the throttle plates to close a bit more, slowing the idle speed to the point of nearly stalling. If that's not it, check your carb's idle settings.
It's the 350 Rocket engine. Would either of those suggestions make the gen light and buzzer go off at random low idle moments?
It's the 350 Rocket engine. Would either of those suggestions make the gen light and buzzer go off at random low idle moments?
The 350 was available with both a 2bbl and 4bbl carbs. Let us know which one you have. I'm not sure what is causing the buzzing (is it the mechanical voltage regulator, or the key buzzer?), but all I know is that IF your car has an idle stop solenoid (like my '68 350-2bbl does) and it has a loose electrical connection (or isn't bolted to the manifold sufficiently that a good ground is provided), it can cause the intermittent low idle speed (nearly stalling) which can trigger the GEN light. If some buzzing occurs coincidentally with the low idle and GEN light coming on (regardless of where the buzzing is coming from), if you solve the intermittent low idle issue, odds are that the GEN light and buzzing will stop too.
The function of the idle stop solenoid is to close the throttle plates when the ignition is turned off to help prevent dieseling (aka: run-on).
Another possibility is that you have some dirt floating around in your carb that is intermittently interrupting fuel flow to the idle circuit. You'd need to rebuild the carb to correct this. I'd check for other causes first. You might also have a fouled plug that is causing an intermittent mis-fire, or a sticking valve that isn't closing consistently that is contributing to the mis-fire.
Last edited by JohnnyBs68S; Jun 10, 2020 at 06:52 AM.
The 350 was available with both a 2bbl and 4bbl carbs. Let us know which one you have. I'm not sure what is causing the buzzing (is it the mechanical voltage regulator, or the key buzzer?), but all I know is that IF your car has an idle stop solenoid (like my '68 350-2bbl does) and it has a loose electrical connection (or isn't bolted to the manifold sufficiently that a good ground is provided), it can cause the intermittent low idle speed (nearly stalling) which can trigger the GEN light. If some buzzing occurs coincidentally with the low idle and GEN light coming on (regardless of where the buzzing is coming from), if you solve the intermittent low idle issue, odds are that the GEN light and buzzing will stop too.
The function of the idle stop solenoid is to close the throttle plates when the ignition is turned off to help prevent dieseling (aka: run-on).
Another possibility is that you have some dirt floating around in your carb that is intermittently interrupting fuel flow to the idle circuit. You'd need to rebuild the carb to correct this. I'd check for other causes first. You might also have a fouled plug that is causing an intermittent mis-fire, or a sticking valve that isn't closing consistently that is contributing to the mis-fire.
Thanks for the detail! Any simple was to figure out if I've got the 2bbl or 4bbl?
These images I just grabbed off the Internet. None-the-less, you should be able to identify the difference between the 2 bbl & 4 bbl by these images. Of course, we don't know if you have in fact the OEM carburetor or an aftermarket, or whether the carburetor is correct for your model year and engine - folks often change out carburetors.
Is the alternator belt tight enough?
Points or HEI distributor?
If the RPM drops too low this will happen. The charging voltage will drop below the battery voltage, which means the engine is running off the battery only. Thus illuminating the GEN light. (bad alternator diodes will do the same).
Once the system voltage drops below spec it will affect the ignition. Remember the running VDC of the ignition is 8-9 VDC. Going below that the ignition won't work.
When you start it back up, RPMs are higher and the alternator could be charging.
What is the charging voltage while it's running at normal warm curb idle...650-750rpm?
What is the battery surface charge after the car sits for a while(not running)?
Have you load tested the battery? If no do it.
Are both ends of both battery cables clean & tight? Are the cables serviceable? If they are 52 years old consider replacement with OEM cables.
The buzzing sound is the regulator. It may or may not be OK depending on how the charging voltage looks.
If the charging system is in question, I have the procedure on how to verify the alternator and regulator. Or you can take both off and bring them into a reputable rebuilder to test both. Rebuild do not replace with inferior offshore big box junk. If you are hell-bent on replacing it don't turn in the original for a core charge. Take the battery too they will load test it.
Consider replacing the regulator with a high-end solid-state unit...if it tests bad. Or find a USA made mechanical regulator.
Steve.
