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Re: stalling problem continues; help?



At 08:30 AM 4/14/99 -0700, you wrote:
>There are two electrical 'black boxes' in the '81- One is inside the
>cabin and is usually on the under tray by the passenger side. It handles
>care and feeding of the O2 sensor and stuff.
>
>The thing you're ref'ing is the electrical ignition module, located up
>in the rain tray and near the wiper linkage. Some cars (California &
>smog equipped I think) have an additional box there to; a Digital Idle
>Stabilizer. It is removed and the two plugs connected together during
>tune up and testing and reinserted when done.
>
>The Hall Sensor is built into the Distributor. It has a female connector
>that pokes out the side and some cables plug into. Often the wires under
>the cap will get all toasty and brittle. In mine the car ran worse and
>worse until it wouldn't run no more. I tested the wires with a meter
>only to get fooled by connectivity- the would pass electricity but not
>enough to register a proper signal, the same then as no signal at all.
>
>The signal to the coil is pulsed, at least that's what I think also. I
>gota run to work but I think it's the Hall signal that's providing the
>signal.

The coil gets a constant 12V on one side. On the other side, is where the
ignition module controls it. Inside the module is a transistor of some
sort(likely IGBT). This transistor clamps the signal wire of the coil to
ground. Now with a low impedance of the coil, 12V on one side, and almost
ground(the transistor is not quite a perfect clamp) on the other, a large
amount of current flows through the coil. To fire the coil, you turn the
current off quickly, by turning off the transistor. When this happens, you
can see momentary spikes of several hundred volts at the coil signal wire,
as it fires. 

  The Hall signal goes to the ignition module. It provides a constant
angular reference for the module. The module can then use this reference to
accurately time the spark, by clamping the IGBT to saturate the coil(dwell
time), then releasing it to fire. With a faulty Hall sensor, the module may
not get the angular reference points, and may not know when to fire the coil.

HTH,
  Brad


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