View Full Version : Voltage drop when brakes are applied


blackz28x07
02-01-2010, 03:15 PM
Ok so I've been having problems for about the last 7 weeks. My car is in storage and I usually start it up every 2 weeks. Well whenever I apply my brakes I can see the voltage gauge just constantly drop from about 13.7 to 13, sometimes even lower. Sometimes when I apply the brakes the car will die. I can leave the car in any gear with the emergency brake up and the voltage gauge is great.

What would cause my voltage gauge to drop when I apply the breaks?

I hate electrical problems!!! :bang:

wssix99
02-02-2010, 09:14 AM
Are you sure its your brakes and not your foot coming off the accelerator? If its the later, you could have a loose belt or bad alt.

Joshiedoom
02-02-2010, 09:27 AM
Most every vehicle I have been behind GM wise has seen the gauge drop with brake pedel because of the lights. As for dying. Sounds like your alternator is taking a crap under load. Check connections everywhere first.

nemss1
02-02-2010, 09:31 AM
sounds like the alternator going out to me.....

fleetmgr
02-02-2010, 09:36 AM
Voltage drop corresponding with brake lights at idle wouldn't be a problem. Engine dying when applying the brakes may mean a vacuum leak in the brake booster, not an alternator problem.

nemss1
02-02-2010, 09:40 AM
Voltage drop corresponding with brake lights at idle wouldn't be a problem. Engine dying when applying the brakes may mean a vacuum leak in the brake booster, not an alternator problem.

it could be either actually. when applying the brakes, RPMs drop which in turn spins the alt slower. had a bad alt on mine and seen voltage drop at low RPMs, braking or at idle, which the OP didnt specify idle. and no i didnt have a vac leak...but yes, it could be that also

fleetmgr
02-02-2010, 09:55 AM
it could be either actually. when applying the brakes, RPMs drop which in turn spins the alt slower. had a bad alt on mine and seen voltage drop at low RPMs, braking or at idle, which the OP didnt specify idle. and no i didnt have a vac leak...but yes, it could be that also
If the voltage drops enough that the engine dies, I wouldn't expect it to be able to charge the battery either. Either that or it's idling to slowly to begin with. If it kills the engine while at speed, I'd expect to see fried wires from the current draw.

nemss1
02-02-2010, 10:05 AM
If the voltage drops enough that the engine dies, I wouldn't expect it to be able to charge the battery either. Either that or it's idling to slowly to begin with. If it kills the engine while at speed, I'd expect to see fried wires from the current draw.

thats what i get for skimming thru posts and agreeing. i re-read it SLOWLY this time:lol:

*RPMs OK at IDLE with NO BRAKES APPLIED
*ENGINE sometimes dies when BRAKES are APPLIED
*VOLTAGE DROP when BRAKES are APPLIED (vacuum)

my apologies:angel:

blackz28x07
02-03-2010, 12:54 PM
it idles at 750, no problem, it has never died when I'm actually braking from crusing, it has only died when i'm slowly backing up/pulling forward or idling. The only thing I've done to anything with the brakes was change a burned out brake light. I'll check the brake booster so see if there's a vacuum leak. Alternator was tested to be good, but I'll check the connections too. It starts up fine everytime, so I know the bettery is being charged. I'm just so confused how it would do this after only being in storage for 2 weeks.

Edit: Just re-read some posts again, so could a vacuum leak in the brake booster cause the votlage gauge to drop?

blackz28x07
02-21-2010, 05:11 PM
Well I went and looked at all the hoses today and found one that looked like it was burnt and it defently had a hole in it. I took a picture of it with my blackberry, but for some reason it won't connect to the internet right now. I have the hose circled in a pic. does anyone know what hose this is? It connects onto a silver cyldiner on the driver's side valve cover towards the back and goes behind the intake manifold.

http://i49.tinypic.com/119t05j.jpg

fleetmgr
02-21-2010, 06:35 PM
Edit: Just re-read some posts again, so could a vacuum leak in the brake booster cause the votlage gauge to drop?
No, not directly. But a vacuum leak will cause idle problems, and if the idle speed goes low it will cause the voltmeter to drop because the alternator will slow down.

blackz28x07
02-21-2010, 09:33 PM
It idles at 750 when it's in drive, I don't know if that's high or not. I was just wondering if anyone knew what hose that is in the picture I posted. I know forsure it has a hole in it since it's burnt and you can actually see the hole.

eseibel67
02-22-2010, 03:40 AM
That looks like your air injection hose.

It only blows air into the exhaust when the engine is cold, so it wouldn't cause the engine to die when you apply the brakes.

But I would check the brake booster hose. It's in the same neighborhood and it might also be burnt.

Mike Broadway
02-22-2010, 04:27 AM
Don't use your Brakes, will be just fine then LOL !!

blackz28x07
02-22-2010, 07:45 AM
The brake booster hose looked fine. This was the only hose I could see that has a hole in it, and I'm thinking i have a vacuum leak somewhere that isn't bad enough to cause any problems when driving, just when I press on the brakes. When it dies the voltage is fine, I just notice the voltage drop quite a bit when i push on the brakes and hold them there.

blackz28x07
02-22-2010, 02:22 PM
did some more research on the hose that is burnt and found out it's part of the pcv hose system. My buddy had told me that yesterday, but i didn't realize the pcv hose system had that many hoses.

fleetmgr
02-22-2010, 02:43 PM
Bingo...vacuum leak.

Armageddon
02-22-2010, 04:30 PM
The hose you circled above goes from the back of the manifold to the brake booster. If that hose has a hole in it your car is going to idle poorly and die when you apply the brakes.

blackz28x07
03-02-2010, 06:11 PM
Update:

I replaced the part of the hose that had a hole in it and it idles better. The voltage gauge stays right around 13-13.2 the whole time. I know I said I could see it constantly drop from high 13 volts to right at 13, but when I push on the brakes now it stays there. It just seems to drop ac the car warms(I guess as the idle lowers since it's getting warm). I haven't really been able to check to see if it will stall on me since I've only started it once since then. I'll start it tomorrow and drive it around and I'll be driving it around quite a bit this weekend since it'll be nice. I'll let you all know if it's for sure fixed.

Thanks for all the help guys!

blackz28x07
03-05-2010, 01:27 PM
Well some more bad news. I took the car out and was driving it for a while, which it did fine. It held about 13.5 volts the whole time. I went to visit my buddy at an autozone store and when I went to leave the car stalled on me. I couldn't restart it because i had no power what so ever. I finally messed with the wiring on the drivers side to see if maybe the exciter wire was giving me trouble. I can't see the exciter wire at all. Well I went to see if it would start and it did. My buddy tested the alt and battery and both were good. What the hell is wrong with my car? I'm leaning more towards the exciter wire, but if that was bad why would I have no power at all when i turn the key for only accecories?

Edit: So I'm retarded. I had a sub and amp in my car, but took it out when I put it away. I had the amp power cable hooked up to the positive cable to the fuse box. I never tightened the damn bolt back down after I unhooked it :bang: I feel so damn stupid haha. Thanks for everbody's advice though, it did help me find that burnt hose.