Idle too low low to charge - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Greasey Harley · 11-17-2020, 03:38 AM

I recently did some upgrades to the ol truck and ended up draining the battery while testing all the systems. Then I warmed it up and took a screwdriver to the 2jet. got it idling real good, nice and smooth, about 550 rpms, sweet... Not so much.
At 550rip'ems the alternator puts out 11.50 volts with the radio on low and the heater on. With a minimal charge on the battery and a 10 minute warm up this morning the battery was at a deficet. Drove 4 miles to work ( not enough to charge) and my battery was dead after work. Good thing I parked on a hill. Anyways, after a little head scratching, I think I have it figured out. --->I tuned the carb too dang good.

I readjusted the Idle up around 650rpm, the alternator stabilized at 13.2v with the radio on and the heater on high, 13.1v if the park lights are on too. Bummer, the thing sounded sweet at a 550 rpm.

skip99 · 11-17-2020, 11:07 AM

Change pulleys

Andy4639 · 11-17-2020, 07:22 PM

Did you check the belts and tension on the alternator belt.
It could be slipping are just not tight enough.

Dead Parrot · 11-17-2020, 08:30 PM

Which alternator do you have? A 12SI has about 7 more amps at engine idle speeds then the older 10SI.

Greasey Harley · 11-17-2020, 10:04 PM

Quote:

Originally Posted by skip99

Change pulleys

Stock pulleys seem fine, It didn't cost anything to bump the idle up a few rpm.

Quote:

Originally Posted by Andy4639

Did you check the belts and tension on the alternator belt.
It could be slipping are just not tight enough.

It might be a tiny bit loose, the belt chirps at high rpm, it wasn't slipping at idle though

Quote:

Originally Posted by Dead Parrot

Which alternator do you have? A 12SI has about 7 more amps at engine idle speeds then the older 10SI.

It's a 10DN, still rockin' the regulator on the core support.

The truck seems great now, drove it all day. no problems.

Andy4639 · 11-18-2020, 12:42 PM

Remember a alternator is not meant to charge up a dead battery. That is the worst thing you can do with it. If your battery is dead charge it with a charger. I know if your stranded you can't but I'm talking about when you do it at home. Put it on the charger. Let it fully charge before you test it. If it wasn't fully charged when you tested the battery out then that's why.

From your response you have a straight drive so the RPM @ idle is a little lower than a auto. Don't know for sure what model you have but a 67-72 C-10 straight drive stock motor is about 650-700 @ idle. If you have a different cam then it would be something else. When warm.

**VetteVet** · 11-18-2020, 02:41 PM

The newer CS alternators output more amps at idle to make those headlights brighter and charge the battery better. Just saying.

**'68OrangeSunshine** · 11-26-2020, 03:38 PM

R&R the EVR. It's getting hard to get a good one anymore.
Still using it on my '68 C/10 w/292. My Checker Auto lifetime warranty gets me a low quality replacement from O'Reilly's. This one charges now, but I get the RED GENERATOR light on the dash when I pull the key out. For now, a good thunp on the left front fender [below the reflector] shocks the body enough to free the sticking contact inside the regulator.

On my '71 GMC Jimmy, w/350 I got a new-built 12SI [for a " '76 GMC"] alternator, and connected some wires before the EVR connection. [F + 3, 1 + 2]. Different inputs to the back of the Alternator, and now it works great.

11-17-2020, 03:38 AM	#1
Greasey Harley Registered User Join Date: May 2013 Location: Post Falls, ID Posts: 884	Idle too low low to charge I recently did some upgrades to the ol truck and ended up draining the battery while testing all the systems. Then I warmed it up and took a screwdriver to the 2jet. got it idling real good, nice and smooth, about 550 rpms, sweet... Not so much. At 550rip'ems the alternator puts out 11.50 volts with the radio on low and the heater on. With a minimal charge on the battery and a 10 minute warm up this morning the battery was at a deficet. Drove 4 miles to work ( not enough to charge) and my battery was dead after work. Good thing I parked on a hill. Anyways, after a little head scratching, I think I have it figured out. --->I tuned the carb too dang good. I readjusted the Idle up around 650rpm, the alternator stabilized at 13.2v with the radio on and the heater on high, 13.1v if the park lights are on too. Bummer, the thing sounded sweet at a 550 rpm. __________________ Insert clever text here: Last edited by Greasey Harley; 11-17-2020 at 03:44 AM.

11-17-2020, 11:07 AM	#2
skip99 Registered User Join Date: Oct 2010 Location: mt vernon, oh Posts: 867	Re: Idle too low low to charge Change pulleys __________________ Tami's 51 build http://67-72chevytrucks.com/vboard/s...d.php?t=428878

11-17-2020, 07:22 PM	#3
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Idle too low low to charge Did you check the belts and tension on the alternator belt. It could be slipping are just not tight enough. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

11-17-2020, 08:30 PM	#4
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,472	Re: Idle too low low to charge Which alternator do you have? A 12SI has about 7 more amps at engine idle speeds then the older 10SI.

11-18-2020, 12:42 PM	#6
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Idle too low low to charge Remember a alternator is not meant to charge up a dead battery. That is the worst thing you can do with it. If your battery is dead charge it with a charger. I know if your stranded you can't but I'm talking about when you do it at home. Put it on the charger. Let it fully charge before you test it. If it wasn't fully charged when you tested the battery out then that's why. From your response you have a straight drive so the RPM @ idle is a little lower than a auto. Don't know for sure what model you have but a 67-72 C-10 straight drive stock motor is about 650-700 @ idle. If you have a different cam then it would be something else. When warm. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

11-18-2020, 02:41 PM	#7
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,703	Re: Idle too low low to charge The newer CS alternators output more amps at idle to make those headlights brighter and charge the battery better. Just saying. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

11-26-2020, 03:38 PM	#8
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,022	Re: Idle too low low to charge R&R the EVR. It's getting hard to get a good one anymore. Still using it on my '68 C/10 w/292. My Checker Auto lifetime warranty gets me a low quality replacement from O'Reilly's. This one charges now, but I get the RED GENERATOR light on the dash when I pull the key out. For now, a good thunp on the left front fender [below the reflector] shocks the body enough to free the sticking contact inside the regulator. On my '71 GMC Jimmy, w/350 I got a new-built 12SI [for a " '76 GMC"] alternator, and connected some wires before the EVR connection. [F + 3, 1 + 2]. Different inputs to the back of the Alternator, and now it works great. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not.



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