Putting my car all back together. Got engine running; 2.0 liter with weber carbs. Had alternator checked prior to installing back on car and it was fine. Last night, while the engine was running, I removed the negative battery cable to see if engine would keep running (off alternator output). The engine died. Seems odd. Is this normal for a Porsche 914?

I never tried removing a ground cable from a running car. It is always best to remove the ground cable if you want to isolate the car for doing work on it but on a running car I think that is different. In this case I would only remove the positive. Actually I would never remove a battery cable on a running car but that is just me. Is your car operational now?

Please don´t do this you can kill the Alternator with this.


http://www.troubleshooters.com/dont_disconnect_battery.htm



Gruss Ralf

thanks for the tip

Will use my multimeter to measure voltage output.

[quote name='914fahrer' date='Mar 3 2016, 12:49 PM' post='2310865']
Please don´t do this you can kill the Alternator with this.


http://www.troubleshooters.com/dont_disconnect_battery.htm

Exactly, this is why kill switches for alternator cars have the ground safety wire path; engine still turning alt. and it's making current, with no path back to battery.

Last time I did that on my 6, it cost me $400.00

Don't ever, EVER disconnect the battery when the engine is running on a car with an alternator.

Very basically, an alternator will attempt to deliver the amount of current it deems necessary. When you remove the battery from the circuit, the alternator sees infinity and attempts to deliver.

You either need a new alternator or a new voltage regulator (or both).

Bad 914 guy. Don't do that again.

Yup. that is a no-no on just about any car, per the reasons Joe outlined. I'm curious if you alternator light is on now? Have you started it since then? Might have dodged a bullet, but very possible the voltage regulator or alternator diodes are fried.

I got lucky. Did some checking with my volt meter. Battery is a 12.6 V. Started car and no increase if Voltage. Thought I mush have messed up the alternator.

Did some more checking and luckily, I had forgotten to re-hook up the 3 prong alternator connector to the relay board. Saw that this morning. Will start back up later today.

Learned from the forum to not unhook a battery lead with a running engine. Guess I have been lucky in the past as that is a sure way to test if the alternator is putting out, but understand it's a bad idea.

Yep, once the car is running, you have to think of the battery as a big filter capacitor, keeping the crappy pseudo-DC put out by the alternator smoothed out. Remove the filter cap, and all that noise energy doesn't play nice with the other components in the electrical system.

Gary

In my case it fried my CDI unit.