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Run without a battery?

nope, electronics run off the battery, which is charged by the alternator. disconnect the battery, and you break the supply of electristy to the vehicle. only diesels can run with a dead/diconnected battery.

are you doing this to check the alternator?

voltmeter is your friend, bat alternator is about 12v, good alternator is around 14.4v
 
Ran my truck for a while with no battery (was a 350 gas motor at the time).

It ran but some weird stuff happened (gauges stopped working or did weird stuff, wipers worked but at 10% speed, etc.

My guess is the ground on the battery is pretty important to the electrical system but I don't really know :dunno:
 
K5dreamer said:
thats very confusing to me....
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I agree, but I guarantee that I did it.

The battery in my friends Rubicon went bad (so bad that it had enough internal resistance that the truck wouldn't take a jump) so I started my truck then disconnected the battery and put it in the Rubi.

Drove it like that from Grand Junction to Denver (a couple hundred miles).

Of course, a '77 Blazer doesn't draw a whole lot of electrical power during the day ;)
 
i guess id have to look again at the wiring schematics of those years, but my memory banks put the battery in-line between the alternator and the chassis, meaning removing the battery opens the circiut... no power.

im not calling you a liar, you obviously did it, i must just be missing something from the brain bank.... maybe a power supply line from the alternator to the starter, and then to the chassis?????? i dunno.
 
All vehicles that aren't electric (duh) will run with the battery disconnected if the alternator is working. The best way to blow an alternator is to unhook the battery with the engine running (good chance to blow the diode trio). There is a point when the engine will stop though and if it is a carbed vehicle that happens around 9.2 volts and if it's a fuel injected vehicle it will happen when the voltage is even higher (numerically) than that as the ECM needs a certain amount of voltage for the sensors to work properly.
 
K5dreamer said:
nope, electronics run off the battery, which is charged by the alternator. disconnect the battery, and you break the supply of electristy to the vehicle. only diesels can run with a dead/diconnected battery.

are you doing this to check the alternator?

voltmeter is your friend, bat alternator is about 12v, good alternator is around 14.4v
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I've had this occur before on my mom's 97 Sub. I was told to disconnect battery to check alternator. Then my mechanic said NO! because of the electronics on the EFI. My question for further reference, is where to I connect the leads of the voltmeter to properly test? Thanks!
 
CAVANALK5 said:
I've had this occur before on my mom's 97 Sub. I was told to disconnect battery to check alternator. Then my mechanic said NO! because of the electronics on the EFI. My question for further reference, is where to I connect the leads of the voltmeter to properly test? Thanks!
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 You can check the Voltage at the battery terminals. Then check it at the alternator with the positive lead on the output post and the negative lead on ground. Testing at both places will tell you if you have a voltage drop between the alt. and the battery.


And for clarification, won't a carbed engine with points ignition will run indefinitely with the battery unhooked?
 
On the back of the alternator, there is one larger power post, normally with a red cap over it. THis wire feeds directly to the postiive terminal on the battery. That is where the alt wire would run into the rest of the system w/ the battery disconnected.

To test teh alt, put the red probe on your volt meter on this post directly, and the neg probe on a good clean piece of metal, or the neg terminal on teh battery. The neg terminal on the battery is connected to a stud on the passenger front side of the intake manifold, right behind the water neck. THis is a good place to touch that probe too. As stated, it should be well above 12 volts, probably 14-14.4.

If its less than that, you probably need an alternator. The alt is super easy to change, as long as you know how to remove the belt. If you take your alt in, most parts stores will test it for you too!
 
AKbigsub said:
And for clarification, won't a carbed engine with points ignition will run indefinitely with the battery unhooked?
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No, it takes a minimum of about 9-9.3 volts to make the system work. When voltage drops below that level the engine will die.
 
spark ignited engines need spark, IE electric current. No juice, no bang.

im still fuzzy on how power gets from the alternator to the rest of the system with the battery out of the circuit, but as i said, id need to look at the schematic.
 
The easy to understand answer is that the alternator charge wire doesn't hook directly to the battery lug, it usually attaches to a junction block on the firewall or down at the starter where the wire that needs power to make the rest of the truck run goes to. (power wire from ignition switch attaches to the large lug on the stater VIA the junction block on the firewall where the alternator charge wire connects).
 
I have ran older cars without a battery. Had a dead short in a battery once. pulled the battery out. Jumped the car and drove about 50 miles without the battery in the circut. Runs fine as long as you dont use any other power other than the ignition. Not a good idea tho. As said it can blow the diodes.
Would not do it on a newer computer controled vehicle.
 
Thunder said:
I have ran older cars without a battery. Had a dead short in a battery once. pulled the battery out. Jumped the car and drove about 50 miles without the battery in the circut. Runs fine as long as you dont use any other power other than the ignition. Not a good idea tho. As said it can blow the diodes.
Would not do it on a newer computer controlled vehicle.
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Yup older cars can be but the newer computer controlled cannot...How ever to get out of a tight spot you could hook up a jump box and leave it to get home.....I was wheeling with a friend that didn't have his battery secured and of course we busted it...used his jump box to start the truck and it died as he un-hooked it so we ended up just leaving it attached and driving home on it....
 
My efi honda prelude will run with the battery disconnected. I know cause the battery is always dead since we never drive it. The alternator and battery are connected in parallel so if one isn't there, the other will provide power. Just because the battery is disconnected doesn't mean the computer isn't connected to a power source.

After all, removing the alternator lug doesn't cause the motor to stop running, since the battery will power it for as long as it can before getting too low.
 
Capt.D said:
Yup older cars can be but the newer computer controlled cannot...How ever to get out of a tight spot you could hook up a jump box and leave it to get home.....I was wheeling with a friend that didn't have his battery secured and of course we busted it...used his jump box to start the truck and it died as he un-hooked it so we ended up just leaving it attached and driving home on it....
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Posted in "Trail Fixes" thread???
 
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