I am having trouble getting a signal on my scan tool for RPM's while cranking. After the car starts, I have a reading, but I don't have one while engine is cranking. Exactly where does this signal come from? I am using an OTC 4000e if anyone needs to know.

 

If I'm not mistaken, everything shuts off while cranking the engine, all sensors and electrical equipment of all sorts, except for the necessary parts. I know the power windows will stop, the radio will stop, my digital dash goes out, and just about everything else. I assume this means the tach signal from the computer would go out too.
Corry

 

Freeze,

The crank signal is derived from the distributor reference pulses at the HEI module. The pulses are connected to the ECM at terminals B3 and B5. If the reluctor, pickup coil, or amplifier/switch module (HEI) is failing, you may not get the reference pulses the ECM needs. If this were the case, you should also get no spark. Thus, if the car starts, your scanner may not be funtioning properly, or the components may be getting intermittent.

Good luck.

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Later,
Vader
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"Make Me Bad"
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