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by Bob O’Neill and Bob Lincoln
The fuel injector sync signal (on turbo engines) and the ignition reference sensor are provided by the ‘Hall Effect Pickup’ (HEP) sensor. The HEP is located on a plate under the distributor cap and uses a coil on one ‘wall’ and a magnet on the other ‘wall’ between which the shutter in the distributor passes through. TBI engines have one sensor for the ignition, and turbo engines have a second sensor for the fuel injection signal. Therefore, the turbo distributors have two electrical plugs from the HEP, the TBI engines have only one.
As the shutter passes through this it breaks the signal which is then passed to the logic module. These signals are used by the logic module to determine the position of the crankshaft. This information is used by the logic module to determine when to fire the injectors. When cylinder #1 is referenced by the injector reference sensor in the HEP the logic module sends a signal to the power module to fire the injector bank. To locate cylinder #1 the shutters which pass through the walls has one blade with a hole in it. As this blade passes through the walls the signal is different than that of the other blades. Because the distributor turns half as many times as the crank the low pulse happens once for each four rotations of the crankshaft.
Code 54 is triggered if the logic module doesn’t detect a signal from the HEP when the engine is turning. In the 1985 models the power limited light will be lit and the engine will enter limp mode. If this happens the logic model will guess when to fire the injectors and if the logic module senses a signal from the detonation sensor it will apply it to all cylinders. For other model years the engine will not start.
LINKS: Hall Effect pickup | Diagnosing Hall Effect and other sensor issues | Code 54
Sensors, Switches, and Other Systems | Main Repairs Page | EEKs
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