engine dies when unhooking battery, alternator dead right??

Roland69 · Apr 23, 2006

your gauge is stock right. Hook a digital volt meter to your battery while running it should read anywhere from 12-14.5 would be fine I would like to see around 13 or 14 myself

freshstang · Apr 23, 2006

what kind of alternator did you get? i put pullies on my car and now at idle i have about 9 v's. but once the car gets above 1500rpm's it picks back up to 13 as long as the headlights or air isnt on. i just bought a 150 AMP alt. that im putting on once i get back. but if you wanted to keep your pullies on and have good voltage, you should have upgraded to a 3G alt. thats a 130 AMP alternator, that at IDLE will be producing at least 14.4 volts, with ud pullies installed. and guys, your replys were very knowledgable, but werent really helping this guy get his car back on the road

hllon4whls · Apr 23, 2006

Daggar said:
Although I'm aware that there is a spike, what I'm not aware of are any spikes sufficient enough to cause elsectrical damage. Anyone ever see damage as a result of disconneting the battery on a Fox?

I didnt see it on a fox, but I did on an 86 150 and 94 nissan sentra.

I can tell you exactly what I did that caused a spike. I disconnected the battery and increased the electrical load and the engine RPM to increase the output.
On the 150 I blew out 2 headlights instantaneously. On the Nissan, I fried the wiper switch. It literally smoked and stayed in the on position forever. Had to replace the unit.

Try it if you like, but I am not doing that again. I didnt believe it the first time so I tried it again.

I'd leave the battery connected and check the output voltage with a DVM. Increase the load even hold the RPMs up a bit to try to increase the voltage.

jrichker · Apr 23, 2006

hllon4whls said:
I didnt see it on a fox, but I did on an 86 150 and 94 nissan sentra.

I can tell you exactly what I did that caused a spike. I disconnected the battery and increased the electrical load and the engine RPM to increase the output.
On the 150 I blew out 2 headlights instantaneously. On the Nissan, I fried the wiper switch. It literally smoked and stayed in the on position forever. Had to replace the unit.

Try it if you like, but I am not doing that again. I didnt believe it the first time so I tried it again.

I'd leave the battery connected and check the output voltage with a DVM. Increase the load even hold the RPMs up a bit to try to increase the voltage.

Proof for the non-belivers from someone who has had first hand experience. May all of us profit from his example...

jrichker · Apr 23, 2006

Foxfan88 said:
ok guys i got it! it was wire going from the starter solenoid to the alternator.

corroded so i spliced some new wire in. it shows up higher on the guage now. But still acts like its not quite up to par. Battery is fine and the Alt is new, How much do UD pullies really affect it. its on the 2nd white line from the bottom.

I have UD pullies, I had the UD alt pulley but now i have a factory sized pulley (changed it today). But its still underdriven since the UD crank pulley is still on the car.

i might try and go back to stock pulleys and see what happens.
but is there anything else to check that would affect it?

well i got a new alt

Check your alterantor power ground. Here's part of my standard tech note on grounds...

Grounds are important to any electrical system, and especially to
computers.

1.) The main power ground is from engine block to battery: it is
the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G alternator needs a 4 gauge ground wire
running from the block to the chassis ground where the battery
pigtail ground connects. The 3G has a 130 amp capacity, so
you wire the power side with 4 gauge wire. It stands to reason
that the ground side handles just a much current, so it needs to
be 4 gauge too.

Picture courtesy timewarped1972

89302guthrie · Apr 24, 2006

i'm no expert, however i was taught that the alternator acts merely as a generator to the battery. The battery supplies the power needed to run the engine directly to the coil. Many racers run without an alternator to save weight and power. i ran ud pullies on my car and did notice a charging problem at idle, that means they're working. Check the voltage at your battery with the car running, at idle it's going to be around 11-12. at about 1500rpm you should come up to 13.7 or slightly higher. if not how fast do you have to go to get that voltage? barely charging a battery all the time can do a number on it, if it's a couple years old, i'd replace it. and think about putting the stock pulley back on.

Foxfan88 · Apr 24, 2006

voltage is fine. 12 off and 15 running.

still seems like it should be getting more.

my friends car has UD pullies and doesnt have as much charging problems as i have.

Where do i hook that ground strap up to on the drivers side firewall.
I have the wire dangling but i dont know where it goes.

jrichker · Apr 24, 2006

Foxfan88 said:
voltage is fine. 12 off and 15 running.

still seems like it should be getting more.

my friends car has UD pullies and doesnt have as much charging problems as i have.

Where do i hook that ground strap up to on the drivers side firewall.
I have the wire dangling but i dont know where it goes.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

Picture courtesy of timewarped1972

Bolt one end of the 4 gauge wire to the engine block where the battery grounds. Bolt the other end to the common ground point on the driver's side chassis where the screwdriver is pointing to in the above photo.

brammabull69 · Apr 24, 2006

start your car and put a screwdriver to the back of the alt. it should be magnetic right? that is what i was told but have never tried it.

engine dies when unhooking battery, alternator dead right??

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