Please help
10-24-2010, 03:10 PM
#1
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Please help Ok I'm not sure where to post this question. I know its not a lt1 or ls1 question,but there seems to be much more knowledgeable people on here than any chevy truck website I can find. I just bought a 91 1/2 ton chevy last night with a 350 and auto trans. The truck fired right up and drove home 60 miles just fine. Long story short when the engine is warm it turns over very slowly almost like the battery is dead. When its cool it spins over just fine. I just took my battery tester out there and did a load test and it test fine. Then I cranked the engine and the voltage drops down to 8-9 when cranking warm. Again I know this isn't my camaro but really hoping you guys can help me out.
10-24-2010, 07:31 PM
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Yeah I know, but all this country *** auto parts in my town does is hooks 12 volts to it and sees if it spins. I'm just going to change the starter tomorrow and hopefully that will fix it. Ive had vehicles turn over slow when warm before due to timing but I'm guessing its something to do with this voltage drop. Thanks for the reply
10-24-2010, 08:59 PM
#5
Depends on where your losing voltage at. If you are losing voltage at the starter its either a bad ground or positive wire/connection. If your losing voltage across the battery terminals themselves it's either the battery itself or a major load pulling down the voltage. My guess would be poor ground connection.
10-24-2010, 09:30 PM
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Depends on where your losing voltage at. If you are losing voltage at the starter its either a bad ground or positive wire/connection. If your losing voltage across the battery terminals themselves it's either the battery itself or a major load pulling down the voltage. My guess would be poor ground connection.
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10-24-2010, 09:59 PM
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Thanks for the reply. So a bad starter can cause a large voltage drop across the battery terminals? I know it seems I'm asking too many questions but I'm laid up in a back brace from a broken back and am going to have to pay a buddy to do something simple like a starter swap I just wanted to make sure that is the problem. I'm trying to get this truck right so when I get out of this damn brace Ill have transportation to work.
10-24-2010, 10:55 PM
#9
The starter is an electric motor, if it's not working properly it uses more power to spin and turn the engine over, thus the reason you're seeing a drop in voltage from the battery. And seeing you have no idea how old the starter is since you just bought the truck, it would be wise to replace it if you plan on keeping the truck for a while. SO even if it doesn't fix the problem you know you'll have a good starter.
10-25-2010, 10:57 AM
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The starter is an electric motor, if it's not working properly it uses more power to spin and turn the engine over, thus the reason you're seeing a drop in voltage from the battery. And seeing you have no idea how old the starter is since you just bought the truck, it would be wise to replace it if you plan on keeping the truck for a while. SO even if it doesn't fix the problem you know you'll have a good starter.
10-26-2010, 10:54 AM
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Thanks for the advice. The starter fixed me up. Its spinning over great now. I still have the voltage drop when cranking. I dont know if thats what killed the last starter. I guess time will tell if the drop will cause poblems,but for now Im good.
10-26-2010, 11:52 AM
#12
this is not necessarily true. Generally they (electric motors) use less power when not working. When they use more, it's because the motor is loaded or overloaded or undervoltaed.
you can't really conclude one way or the other from seeing a voltage drop across the battery terminals, whether it's a large voltage drop or not, to the condition of the starter. Generally if you see a large voltage drop it's usually because of a weak battery.
What can happen is the brushes and the armature they contact in the starter can become dirty and corroded and prevent current from flowing into the armature, so the starter would turn slowly and not have power and you would see much less voltage drop across the battery than you normally would. And depending on the type of starter and what solenoid it uses, it could be a bad solenoid.
10-26-2010, 11:58 AM
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this is not necessarily true. Generally they (electric motors) use less power when not working. When they use more, it's because the motor is loaded or overloaded or undervoltaed.
you can't really conclude one way or the other from seeing a voltage drop across the battery terminals, whether it's a large voltage drop or not, to the condition of the starter. Generally if you see a large voltage drop it's usually because of a weak battery.
What can happen is the brushes and the armature they contact in the starter can become dirty and corroded and prevent current from flowing into the armature, so the starter would turn slowly and not have power and you would see much less voltage drop across the battery than you normally would. And depending on the type of starter and what solenoid it uses, it could be a bad solenoid.
you can't really conclude one way or the other from seeing a voltage drop across the battery terminals, whether it's a large voltage drop or not, to the condition of the starter. Generally if you see a large voltage drop it's usually because of a weak battery.
What can happen is the brushes and the armature they contact in the starter can become dirty and corroded and prevent current from flowing into the armature, so the starter would turn slowly and not have power and you would see much less voltage drop across the battery than you normally would. And depending on the type of starter and what solenoid it uses, it could be a bad solenoid.
10-26-2010, 12:11 PM
#14
the voltage drop is normal, any time you put an electrical load on the battery the voltage across the terminals will drop whether it's a fraction of a volt or 2-4 volts.
I don't know for a starter as old as for a '91 truck but the starter for the LS1 and similar PMGR starters are all rated at 1.4kw or 1.7kw, ( 1hp = 746 watts, 1.7kw = 2.27hp )
so to pull over 1000 watts from the battery, there will be sizeable voltage drop.
car batterys are rated via their CA (cranking amps @ 32F) or CCA (cold cranking amps @ 0F) which is the amount of amps the battery should be able to provide for 30 seconds without the voltage across the battery terminals dropping below 7.2 volts. Generally the voltage on a good battery will drop down around 10-11 volts when using the starter. When voltage drops below 10 it's because of a weak battery.
10-26-2010, 05:01 PM
#15
the voltage drop is normal, any time you put an electrical load on the battery the voltage across the terminals will drop whether it's a fraction of a volt or 2-4 volts.
I don't know for a starter as old as for a '91 truck but the starter for the LS1 and similar PMGR starters are all rated at 1.4kw or 1.7kw, ( 1hp = 746 watts, 1.7kw = 2.27hp )
so to pull over 1000 watts from the battery, there will be sizeable voltage drop.
car batterys are rated via their CA (cranking amps @ 32F) or CCA (cold cranking amps @ 0F) which is the amount of amps the battery should be able to provide for 30 seconds without the voltage across the battery terminals dropping below 7.2 volts. Generally the voltage on a good battery will drop down around 10-11 volts when using the starter. When voltage drops below 10 it's because of a weak battery.
I don't know for a starter as old as for a '91 truck but the starter for the LS1 and similar PMGR starters are all rated at 1.4kw or 1.7kw, ( 1hp = 746 watts, 1.7kw = 2.27hp )
so to pull over 1000 watts from the battery, there will be sizeable voltage drop.
car batterys are rated via their CA (cranking amps @ 32F) or CCA (cold cranking amps @ 0F) which is the amount of amps the battery should be able to provide for 30 seconds without the voltage across the battery terminals dropping below 7.2 volts. Generally the voltage on a good battery will drop down around 10-11 volts when using the starter. When voltage drops below 10 it's because of a weak battery.
And always remember that when you have electrical resistance amperage goes down and when you have mechanical resistance ( dragging starter tight motor etc.) amperage goes up. So if you see a ground cable smoking or something of that nature you know you have a mechanical type of resistance.
10-26-2010, 06:06 PM
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Ok that makes me feel better. I always thought you were not supposed to see more than .5 voltage drop. Its dropping down to about 9-10 but still firing fine. I guess its all good.
10-26-2010, 07:09 PM
#17
Your welcome, I'm glad to hear a new starter fixed the warm starting problem. I don't know much about electricity such as amps and ohms, but I do know if something gets hot and doesn't work properly that the mechanical parts need to be replaced. I'm a toolmaker/machinist so I know a lot about the correct fit and operation of mechanical assemblies.
