Ford Enthusiast

[ABE]

The typical problem is that you try to start your car and the battery is flat. But it was OK yesterday. So you get the battery charged or boosted, but it happens again. So you get it charged off the car and clean it up and when you re-connect (pos first) the neg cable there is a blue spark, a noticeable crack and then it is connected and everything seems OK, but it is not.

With all the accessories on the car switched off there should only be a small drain on the battery from the PCM and the sensors that manage the safety and operations of the car. The load should be about 2.2 amps if you have left a door open and only 0.240 amps (240 milleamps) if not and this produces a very small white spark. The 240 milleamps will drop to 20 to 40 milleamps over the next 30 mins as the sensors are put to sleep if you do nothing to the car. That rate of discharge will allow the battery to start your car after a month of sitting somewhere.

The overnight drain and blue spark show a large drain on the electrical system. The first suspect is one of the alternator's diodes which may be draining the battery to ground. Disconnect the battery and put an ammeter between the neg post on the battery and the neg cable and note the reading and disconnect. Remove the heavy battery cable from the alternator and safely insulate the connection from grounding. Remove the remaining alternator connections to isolate the alternator. Now reconnect the ammeter and note the reading, if the reading has dropped significantly replace the alternator because you have a failed diode feeding battery current to ground through the alternator.

If the ammeter is reading between 20 milliamps to about 240 milliamps the problem is solved, but keep it connected to see that after a further 30 mins it does drop to at least 40 milliamps or lower.

If the reading is higher then one of the car's electrical systems has a problem, but how to find it. Make sure all the electrical systems are switched off and the driver's door or any access to the fuse panels are open. Disconnect the neg cable from the battery and connect a digital multi-meter set to record DC amps between the neg battery terminal and the neg battery cable, secure the connections so that they stay connected (i.e. alligator clip, length of wire, etc). Record the time and the amps and wait for 35 minutes for the PCM and all sensors to go to sleep, but still monitoring. Record the time and amps.

Now you start to pull the fuses that govern the likely circuits causing the drain. However, once you pull a fuse do not put it back because that will likely wake a sensor and since all the sensors are connected with the PCM you will be back to the 2.2 amp draw due to the GEM (Generic Electronic Module) switching on the door lights, etc. So keep a record of the circuits disabled, the fuse # and size and where the fuse is now that it is somewhere safe outside the car. Do it one fuse at a time and keep checking the ammeter to note a change in reading until all the draining circuits are found and the ammeter is registering 40 milliamps or less.

Disconnect the ammeter and repair the circuit, and re-install all the fuses in their correct places as recorded earlier.

Reconnect the ammeter and verify the repair, by watching the ammeter as it shows a reducing amp draw over the 30 minutes after re-connection. If you are down to 20 to 40 milliamps the problem is fixed and you can reconnect the battery.

Hope this helps.