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The first thing your looking for is a clean way to pick up the signals without causing damage to the wire harness. I try very hard to avoid any nicks at all to my wire harness. It can often be done but takes extra effort. For test measurements you may be able to take a single fine strand wire slide into the socket of the connector then routed out through the protective boot. If done carefully you can pinch that strand in the connector pin as it's plugged together. To get fine strands of copper wire just strip a length of wire and separate the strands. Use wire that has fine strands.
Most injectors will have ignition voltage on one side of the coil and the other side of the coil is switched to ground by the engine controller. On the engine controller side of the injector you will see near battery voltage when the injector is off and the voltage will drop to near ground when the injector is on. When the injector is turned off you will see a large spike that is caused by inductive kick back from the coil. The length of the pulse will vary with the load on the engine. You may need to hold the break and load the engine down with the clutch to see much variation sitting still. I should get longer when you rev the engine but not as much as when you really put a load on the engine.
you may see the signal drop low for the duration of the injector pulse then return high. This is the most common and is a direct connection to the MPGuino.
You may see the signal drop low briefly then make several very short pulses before releasing. This is called a pulse and hold drive signal. It can be handled but takes additional circuitry.
If you see anything else then try to describe it or better yet post a picture. While your playing with the scope try to get a good measurement of the low voltage when the injector is on. If the low point is more then about 0.25 volts you can add a resistor to create a voltage divider on the input and reduce the voltage to the processor pin.
If you have an electronic speed sensor take a look at the output. It will likely either be nice digital on/off or it will be a sine wave that gets smaller when you slow down to a stop. If it's the sine wave type it may have external diodes that shape it sort of like a square wave at higher speeds so you need to look at the signal down to a stop.
If you have nice digital pulses down to a stop it connects dirrectly. If you have the sine wave type a simple external input circuit will improve performance at low speeds.
Mike
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