truck wont stay above 12 volts - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rays68 · 02-20-2005, 03:33 AM

When I drive my truck around the volts are fine with radio on and air condition or heat on. As soon as I stop at a light or let the truck idle the volts drop to about 10 and the truck starts to run rough and wants to shut off but if I turn the air or heat off while stop or idle the volts go back up to 13-14 and truck is ok. I thought it was the alternator so I put another 63 amp but still no change so I changed the alternator again form a 63 amp to a 94 amp and it still doing the same thing also checked the battery and it shows it puts out 12 volts not sure what to do now any ideas.

r0lf- · 02-20-2005, 03:36 AM

My truck does this too, just not to your extreme, I swapped alternators with my old truck, no go. Im thinking about putting on an underdrive pulley on the alternator just to keep it spinning fast, but I feel the problem is somewhere else, have you checked your grounds and all that fun stuff?

jeffs98 · 02-20-2005, 10:05 AM

You have a ground problem from either your cab to motor or motor to frame!! Try putting a set of jumper cables on the battery and clamping them on to frame and cab and see if this makes it go away!! I have had several of these truck so this and this always works!!

r0lf- · 02-20-2005, 06:19 PM

Hrmmm... Ill have to try that jumper cable trick too.

rays68 · 02-21-2005, 09:02 PM

thanks for the help I will take a look at the grounding wires and also try the cable trick.

rays68 · 02-21-2005, 09:41 PM

ok just checked the ground cables and did the jumper cable trick and it still does the same thing I was looking at my alt belt and it looks kind of old and has lots of cracks on it could this be the problem.

jeffs98 · 02-22-2005, 12:09 AM

Is it loose?? Might be slipping a little and not letting alt. charge fully!! I still say that you have a ground problem though!! It seems that these truck are notorious and especially since you can turn acc. off and it goes away!! Common sympton of ground failure!!

rays68 · 02-28-2005, 04:07 PM

Thanks for all the help I couldnt find the problem so I took it to a firends shop and he told me my idle was way low so he adjusted it and the problem went away again thanks for all the help.

pedrofixlater · 03-05-2005, 06:45 PM

definately a ground or battery problem

gconn77 · 03-06-2005, 03:06 AM

I don't remember where I read this... probably all you guys know this... and correct me if I am wrong, but I believe that the alternator doesn't kick in unless it hits a minimum RPM... the minimum RPM varies from alternator brand and such... reason why I am posting this is because I had the same problem with my car... give it some gas and idle up to about 1400 RPMs and my headlights, dome lights, and instrument cluster doesn't dim and becomes bright again... same with my heater blower... at an idle it blows slow... but give it some gas and idle up to about 1400 RPMS and the blower blows fast again.

TrainD5115 · 03-06-2005, 12:13 PM

Some carbs have an idle compensator that will kick the idle up if the A/C or heater is engaged. If this has been disabled it could also account for your problem with regard to the low idle.

jermasaurus · 03-06-2005, 01:38 PM

on my Monte I would have to rev the motor up to about 2,000 just to get the alternator to start charging. The rest of the day it would be fine. I think having to increase the rpm is sometimes an early warning of a bad alternator. If you are sure that there are no ground problems or connections with high resistance, you may want to look into those alternators that claim 80 amps at idle. They are kind of pricy though.

02-20-2005, 03:33 AM	#1
rays68 Registered User Join Date: Dec 2002 Location: Redondo Beach CA Posts: 131	truck wont stay above 12 volts When I drive my truck around the volts are fine with radio on and air condition or heat on. As soon as I stop at a light or let the truck idle the volts drop to about 10 and the truck starts to run rough and wants to shut off but if I turn the air or heat off while stop or idle the volts go back up to 13-14 and truck is ok. I thought it was the alternator so I put another 63 amp but still no change so I changed the alternator again form a 63 amp to a 94 amp and it still doing the same thing also checked the battery and it shows it puts out 12 volts not sure what to do now any ideas.

02-20-2005, 03:36 AM	#2
r0lf- Hotwheels? Join Date: Dec 2002 Location: Pleasant Hill, CA Posts: 1,145	My truck does this too, just not to your extreme, I swapped alternators with my old truck, no go. Im thinking about putting on an underdrive pulley on the alternator just to keep it spinning fast, but I feel the problem is somewhere else, have you checked your grounds and all that fun stuff? __________________ 1978 Money Pit - CUSTOM DELUXE!!!!

02-20-2005, 10:05 AM	#3
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	You have a ground problem from either your cab to motor or motor to frame!! Try putting a set of jumper cables on the battery and clamping them on to frame and cab and see if this makes it go away!! I have had several of these truck so this and this always works!! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

02-20-2005, 06:19 PM	#4
r0lf- Hotwheels? Join Date: Dec 2002 Location: Pleasant Hill, CA Posts: 1,145	Hrmmm... Ill have to try that jumper cable trick too. __________________ 1978 Money Pit - CUSTOM DELUXE!!!!

02-22-2005, 12:09 AM	#7
jeffs98 Registered User Join Date: Jun 2004 Location: Parsons, Kansas Posts: 139	Is it loose?? Might be slipping a little and not letting alt. charge fully!! I still say that you have a ground problem though!! It seems that these truck are notorious and especially since you can turn acc. off and it goes away!! Common sympton of ground failure!! __________________ 1978 Chevy C-60 Pumper Truck! 1985 Chevy 4x4 project! 2002 Chevy Crew Cab DURAMAX 4x4!! 2002 Harley Road King BIG BORE STG. II, Thunderheader,Dfo Module! 2003 Chevy Malibu!

02-21-2005, 09:02 PM	#5
rays68 Registered User Join Date: Dec 2002 Location: Redondo Beach CA Posts: 131	thanks for the help I will take a look at the grounding wires and also try the cable trick.

02-21-2005, 09:41 PM	#6
rays68 Registered User Join Date: Dec 2002 Location: Redondo Beach CA Posts: 131	ok just checked the ground cables and did the jumper cable trick and it still does the same thing I was looking at my alt belt and it looks kind of old and has lots of cracks on it could this be the problem.

02-28-2005, 04:07 PM	#8
rays68 Registered User Join Date: Dec 2002 Location: Redondo Beach CA Posts: 131	Thanks for all the help I couldnt find the problem so I took it to a firends shop and he told me my idle was way low so he adjusted it and the problem went away again thanks for all the help.

03-05-2005, 06:45 PM	#9
pedrofixlater 75 STEPSIDE Join Date: Mar 2005 Location: Suffolk, VA Posts: 92	definately a ground or battery problem __________________ Pete 75 Chevy Stepside 70 Buick Skylark/GS

03-06-2005, 03:06 AM	#10
gconn77 Registered User Join Date: Feb 2005 Posts: 39	I don't remember where I read this... probably all you guys know this... and correct me if I am wrong, but I believe that the alternator doesn't kick in unless it hits a minimum RPM... the minimum RPM varies from alternator brand and such... reason why I am posting this is because I had the same problem with my car... give it some gas and idle up to about 1400 RPMs and my headlights, dome lights, and instrument cluster doesn't dim and becomes bright again... same with my heater blower... at an idle it blows slow... but give it some gas and idle up to about 1400 RPMS and the blower blows fast again.

03-06-2005, 12:13 PM	#11
TrainD5115 North Coast, baby! Join Date: Jun 2004 Location: Toledo, OH Posts: 437	Some carbs have an idle compensator that will kick the idle up if the A/C or heater is engaged. If this has been disabled it could also account for your problem with regard to the low idle. __________________ Brad 79 Scottsdale C20 350/350 3.73's Still running full CA smog gear!

03-06-2005, 01:38 PM	#12
jermasaurus Registered User Join Date: Dec 2004 Location: New Lenox, IL Posts: 442	on my Monte I would have to rev the motor up to about 2,000 just to get the alternator to start charging. The rest of the day it would be fine. I think having to increase the rpm is sometimes an early warning of a bad alternator. If you are sure that there are no ground problems or connections with high resistance, you may want to look into those alternators that claim 80 amps at idle. They are kind of pricy though.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.