word itz chris

Sup fags, I have a '90 Civic Sedan and every time the car is running and I pull the battery negative, the car shuts off. Ive replaced the alternator and battery, all fuses are good.

Any fucking clue what it could be? This is pissing me off.

LSlowteg

check your charge wire the one from the batt. to the alt. it might go to the fuse box but either way check that or just use a piece of power wire from batt to alt the bypass it to check. And if you got an alt. from advanced or auto zone its not unlikely that the alt is DOA especially if your batt was completely dead when you put the new alt. in

Fabrik8

Check the resistance between the alternator and the battery. It sounds like the alternator isn't charging the battery properly, because if there was an intact circuit between the two then it wouldn't shut the car off. What happens if you remove the positive battery lead? Does the car stay running?

EGAS

Whats your voltage on the battery when the car is running? Theres not much to the wireing on a car. Yet the Voltage system..

Post up some read outs..


EDIT:!!! your car wont run with the negative terminal unplugged from the battery.. i didnt even think about that.. its gonna shut off its suppost to. Youll fry your cars electronics by disconnecting the negative terminal.. If anything your suppost to disconnect the possitive. That will tell you the Alt. is good or bad.. HAhaha i dont know if your joking now or not.

Fabrik8

Not true. The electrical system only needs to have the grounds connected between whatever is supplying power and the load that is consuming it. So if you disconnect the negative battery terminal, the battery is now out of the circuit, and it won't power the car (or be charged). As long as the engine ground is still connected to the chassis ground (because the alternator ground and some sensor/coil grounds are usually connected to the engine) the engine will still run. All of the grounds are in parallel, so if you disconnect the battery ground all of the other grounds don't magically disappear, you just don't have that one ground path anymore so there is no longer a complete circuit to that part.
This is why I asked what happens when he disconnects the positive battery lead, because then the power from the engine has to come from the alternator only.

EGAS

Haha okay yes correct...

Then the problem would lie within the grounding of your system..

Yet by disconnect the battery while the engine is running. You are doing what is called a 'load dump'. The voltage from the alternator can spike up towards 100 volts or so for a split second. Not good for todays vehicles. You cannot count on the alternator keeping the vehicle running in the even of a poor battery connection.

Fabrik8

Anytime you switch off a charged inductive load you get that type of voltage spike. That's what flyback clamps are for. I spend a lot of time protecting our race car power switching circuits against those load dumps because they happen whenever the battery safety disconnect switches get thrown with the engine running. Our alternators are on the battery side of the cutoff switch, so the switch disconnects all power supplies at once.

Anyway, this could just as easily be a power wire problem with the alternator as it could be a problem with a ground. Either way you'd have a disconnected circuit that won't allow the alternator to power the engine with the battery disconnected. Alternators aren't good with the speed and amplitude of the current needed to run the engine when the engine (and inherently alternator) is at low RPM. Batteries are like a great big capacitor in that respect.

CivicRenModelX

+1

CHAHONDA

i can fix it..... for a small fee of course

Jarrod

LOL.
The car sits right down the street from ya too :P

Chris. Sunday, if you hit me up.
We'll follow this advice and try to fix it or at least fix the problem.
Just get me up before the night falls. You know how I like to sleep.