Low voltage shaky at idle. - Vintage Mustang Forums
 
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post #1 of 6 (permalink) Old 07-22-2019, 12:52 AM Thread Starter
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Low voltage shaky at idle.

Last weekend I noticed my 65 289 started shaking a little bit at idle. Drove fine but felt noticeably different when stopped. Tonight I turned on my car and as I was putting the power top down my volt meter started blinking and it was reading 10.7-10.9 volts. I had the car on, radio on and lights on. I’ve never had that problem. When I was idling it read 11.9 and when driving it jumps up to 13+. I turned on the heater motor and when I stopped it dropped back down to ten and started blinking again. Could it simply be a timing/carb issue that’s causing a slower idle which is causing the shaking? I have the newer style electric ford voltage regulator. Haven’t had battery draining issues, yet anyways since I just started having this problem.
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post #2 of 6 (permalink) Old 07-22-2019, 12:56 AM Thread Starter
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I should clarify, when idling it starts at 11.9 but drops down to 10.9-11.3 with the lights on/radio on.
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post #3 of 6 (permalink) Old 07-22-2019, 01:29 AM
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Make sure alternator belt is tight as slipping causes less charging, be sure all grounds and connections on the alternator and battery are clean, a new-ish voltage regulator still can have issues, and it all may be because your idle has fallen too low due to heat, ethanol in the fuel, or any changes that may have been made to ignition timing or carb tuning. Drive it til time to fuel (this is fun) then fill it up with non-ethanol gas, and maybe just drive in the evenings etc when it is cooler and see if this helps before changing anything else. Good luck!

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post #4 of 6 (permalink) Old 07-22-2019, 01:39 AM
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I suspect your alternator or voltage regulator is going bad. You should be able to maintain a normal charging voltage at idle.

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post #5 of 6 (permalink) Old 07-22-2019, 07:45 AM
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Originally Posted by Beatle9999 View Post
Last weekend I noticed my 65 289 started shaking a little bit at idle. Drove fine but felt noticeably different when stopped. Tonight I turned on my car and as I was putting the power top down my volt meter started blinking and it was reading 10.7-10.9 volts. I had the car on, radio on and lights on. I’ve never had that problem. When I was idling it read 11.9 and when driving it jumps up to 13+. I turned on the heater motor and when I stopped it dropped back down to ten and started blinking again. Could it simply be a timing/carb issue that's causing a slower idle which is causing the shaking? I have the newer style electric ford voltage regulator. Haven't had battery draining issues, yet anyways since I just started having this problem.
The battery supplies ~ 12V, so your 10.7-10.9V is the battery. Running on the battery at idle (11.9V) is actually pretty normal.

You may want to check your battery for a weak cell. Also examine the idle speed.

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post #6 of 6 (permalink) Old 07-22-2019, 09:06 AM
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I'm not sure what alternator you have, but it sounds normal to me. Take a look at the alternator output curves below. Even a 1G 60 amp alternator (my car came with a 38 amp 1G) will only put out 15 amps at idle. The lights, ignition coil and radio could easily pull 10 amps, and who knows how much power is sucked-up by the convertible top, but I assume it has an electric motor driving the pump. That's where the battery comes in and you start drawing off of it.

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