Injectors :
The engine I did this test on had a grouped injector circuit 1&3 together and 2&4 togther , that means 1 and 3 would inject fuel at the same time and 2 and 4 together at the same time . You can see the diagram above showing how this circuit in constructed.
Its important to know the voltage supply to the injectors as they should have battery voltage on one and ground wire which gets earthed out by the ECU to turned them on with PWM signal.
we can compare the battery voltage to the injector supply voltage to make sure there is no bad connection , high resistance in the circuit. We do this to make sure the injectors circuit is in a good condition and if they are opening and closing.
Manufactorer spec is voltage drop of less than 0.05 volts is ok .
Battery voltage : 14 Volts
Voltage supply to the injectors 1&3 : 13.96 Volts .OK within manufacturer spec.
Voltage supply to the injectors 2&4 : 13.98 Volts .OK within manufacturer spec.
Throttle Position Sensor:
Reference voltage is the power coming to the sensor via ECU when the ignition is ON . It is important because if this voltage is different from the manufacturer spec then the reading we be getting from the output (signal) wire would be effected . This could be due to high resistance in the ciruit , bad connection ...
Yellow wire
Ignition on , engine off
Refererence Voltage : 4.97 Volts (Good reference voltage and well within manufacturer spec 4.95 - 5 volts)
Ground wire also very important because it also can effect the output signal of the sensor so it can indicate if we have a bad ground orbad connection at the battery terminal or high resistance on the ground circuit . we voltage drop between this wire and the negative battery post to see how much this voltage is and the lower the better and clearer reading we would be getting .
Brown wire
Ignition on , engine on
Ground wire voltage : 0.02 Volts ( Good ground , manufacturer spec is less than 0.05 Volts)
TPS return or output signal is what the ECU uses to determine the driver intent and referece voltage can easily effected with bad and low reference voltage or bad ground or poor connection at the battery terminal which both of these problems would decrease the output voltage to the ECU and because of lower output voltage the computer this would cause to think we are pressing the throttle less than we really are ... this can easily make the engine to perform poorly under load and when the throttle is presses quickly .
we can this sensor to see if we get a reading as we slowly open or slowly close it to check if there is any problems with the carbon strips inside the sensor.
Green wire
Ignition on , engine off
TPS output signal and throttle closesd : 0.581 Volts
TPS output signal and throttle half open : 2.22 Volts
TPS output signal and throttle fully open : 3.95 Volts
