dont get what your trying to say here, can u explain better?

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Last edited by blackjack_original on Fri Jun 06, 2014 6:46 pm, edited 1 time in total.

strange.....im thinking relays, bem, ign barrel....but where do u start....maybe check for current drain when ign is off and try to locate the circuit?

Almost as if its losing the IGN voltage when its cranking. As in, IGN and ACC are now one, but both cutting out on CRANK.


Have you recently installed an alarm, or added diodes to part of the loom?
I once added a diode to my loom so that I could make a particular item work with both IGN and ACC (it needed to run while cranking). The diode eventually blew closed circuit (to an extent) and caused the ECU to get a low voltage when put on ACC. This was enough to make it think it was already on IGN, but there was not enough voltage to power the rest of the components like smartlock, fans etc. It caused the ECU to pop out a handfull of codes and refuse to start.


I would grab a multimeter, set it to current, remove negative lead of an identical car and connect it to the neg lead and neg battery terminal.

Monitor the current draw with the engine off, key out, doors locked (however you normally leave the car overnight.)

Do the same with your car (don't attempt to start the car - you'll blow the multimeter) and see if theres a significantly larger draw. Its important you monitor this with the car in the same state as when you leave it overnight, to eliminate things like door lock actuator positions.

I would suggest replacing multimeter on current above with a small value resistor (0.1 ohm or so, depending on the current to measure) and a multimeter across it on mV range. you are much less likely to blow the meter up this way. If you can get your hands on a (good) clamp meter that will measure DC current, use that.

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Last edited by blackjack_original on Fri Jun 06, 2014 6:46 pm, edited 1 time in total.

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Last edited by blackjack_original on Fri Jun 06, 2014 6:46 pm, edited 1 time in total.

I'd say you have a very intermittant power drain - enough to deep discharge the battery overnight and render it useless.

Have a read of this, its very interesting in regard to sulphation and stratification:

http://www.batteryuniversity.com/parttwo-42B.htm

I would imagine that the above problem would be more gradual, whereas you tend to have a one-off intermittant drain every now and again that flattens your battery overnight. Does the car have anything special on it electrically?

Since finding the fault may take a long time by trial and error, I would suggest trying this. Grab the Jaycar kit KG-9000 Low Voltage Battery Warning ($9.95).

The text states it uses a tiny amount of power (current unknown), so you could leave it connected 24/7. It lights an LED when the voltage goes below a preset level, so I would remove the LED and replace it with a relay card (Jaycar KG-9142, $7.95). Hook up a loud buzzer (or your horn) to the card's relay, so that if you've left the car and its in its "gonna go flat" mode, it'll sound off before it gets too low. At this stage, you can then pop fuses until the problem goes away and the current draw is gone, then check the appropriate circuit.

Just carry your multimeter around with you for a month so you can catch it out.

btw, I would highly recommend the use of the aforementioned highly sensitive clamp meter, as you will most likely need to test this without interrupting the battery connection (in case something is latching on and causing the fault). Even using the door locks could interfere with your testing, but the only way to avoid using them would be to leave the bonnet popped up in your garage (with any alarm inputs bypassed), or leave a window down if it is practical to do so (obviously not on the street in the middle of the day ).

Hope this helps.

Have the alternator checked for discharging the battery (shorted internal diodes) These can drain 5 amps+ in current.

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Last edited by blackjack_original on Fri Jun 06, 2014 6:46 pm, edited 1 time in total.

Because you have an intermittant fault, testing it may not show up anything, taking it to an alternator place would most likely end up in them saying it *may* be faulty and therefore changing the diode pack as a precaution. Not such a bad idea, but it may be more economical to get an entire new alternator should you have to go down that path, if you take brush and bearing wear into concideration.

Regarding the clamp meter usage, make sure you are clamped around the smaller alternator lead when testing the alernator diodes, as well as the main lead and starter lead (individually), as there are several paths for the current to flow for each test.