General lab scope patterns

Task: gather waveforms using a general lab scope from various sensors, First back probe the likely wire for the sensor and attach the lab scobe to get a pattern on the screen.

The 1st pattern i got was the injectors (picture to the right). to do so i back probed the likely input wire to injector one. The 1st horizontal line on the injector pattern is the 12 volt supply to the injector and then at the point where it drops to 0v is when the injector is being switched on by being earth triggered through the ECU. From the point where it was earthed to the point where the line shoots up is the injection time (how long the injector is open for) and the part that shoots up to about 60 volts is due to the coils within the injector discharing, this is also known as back EMF and then the pattern evens back out to the 12v supply until the next earth trigger then this pattern is repeated.

The next pattern i recorded was of the O2 sensor. I back probed the likely output wire of the O2 sensor.

This pattern shows the voltage change that the O2 sensor puts out as the oxygen levels within the exaust manifold changes. This uneven line is due to the change in revs because as i reved the engine silmiltaneosly the voltage would spike up because more oxygen was present. Because this engine i was on was not it closed loop the O2 sensor was not cycling which means that it wasnt switching between running rich and lean to burn the fuel evenly and with less harmful gases.

The next one is of the MAP sensor. The MAP sensor was locate within the ECU on the engine i was on but i could measure it on the sircuit board on the engine stand. The A point on the pattern is the 0 volt line which when the throttle is fully closed is about 0.02 volts because alot of vacuum is present within the intake manifold and as i opened the throttle gradually the voltage output from the MAP would go up which is the slope on the lab scope and then as i slowly let the throttle out and the slope goes down back to 0.02. This is important because the output from the MAP determines the amount of fuel the injectors inject and if the ECU were to receive an incorrect reading from the MAP it would effect the operation of the engine.

The pattern to the right is the waveform of an ECT sensor and what it shows is how the voltage decreases as the Engine coolant temerature increases. When the engine coolant is cold the voltage output from the ECT is between 2.2v and 2.5v and as you can see on the lab scope it decreases gradually as the coolant heats up and eventually when it gets to operating temp it will read about 0.5v. This reading from the ECT is important because when the engine is colt it needs more fuel to get to operating temp so the ECU needs to know the temp of the coolant which it can calculate from the voltage the ECT puts out, and as the coolant heats up it no needs to inject the added fuel.

This next one is the the TPS (throttle position sensor). The TPS on the engine was a 3 wire potentiometer type and i back probed the likely output wire to the ECU. On the scope just above the "A" is a flat line until it starts to slope up, this flat line is about 0.5v and the throttle is completely closed and as i open the throttle to halfway the voltage output goes up to about 2.2v and you can see this on the scope where the line first slopes up. As i open the throttle right up the voltage then increases to about 4.5v. all these different voltage outputs lets the ECU know what position the throttle is at and affects the total operation of the engine.