1.4 Record voltage to an injector by back-probing. 13.8V
We check the voltage supply to the injectors to ensure charging voltage has reached all the injectors. If an injector was reading 0V on a voltmeter while idling, the injector would not be operating and would effect engine performance.
1.5 If a lower voltage is found at the injectors than at the battery, there may be a very high resistance in the circuit. Either from a bad connection, or loose wires. This would effect the amount of time the injector would be open for, which would decrease engine performance due to not enough fuel being sprayed into the combustion chamber.
Below is a wiring diagram of a ignition switch, Battery, Main Relay, and the ECU which controls the switching of the injectors.
Reference voltage at TPS Sensor
2.5
The purpose of the refernce voltage to the TPS is used to compare the signal wire with 5v, and also to supply 5v which is then put through a potentiometer that changes the voltage to the output wire.
2.6
If the reference voltage at the TPS sensor is not correct, the ECU will get incorrect information as to how far the throttle is opened. If the reference voltag was too high, the ECU would read a greae output voltae from the output wire, this would make the ECU think the throttle is opened more then it actually is, increasing the amount of fuel getting sprayed into the cylinders. If the reference voltage was lower, the ECU would think the throttle was closed more then it is, restricting power. The incorrect reference voltage would also effect the gear changes in an automatic vehicle.
Ground at TPS sensor
3.3 Record the voltage ground on a voltmeter. 0.01V
3.3b This tells me that the ground is good, the voltage is close to 000v. This voltage means a short, which is exactly what i'm measuring for.
3.4 Loose connections or faulty transistors could prevent a good ground connection.
Throttle Position Sensor Return/Output
4.2 Record the output voltage from the return wire. 0.65V
4.3 Record the voltage from the return wire when the throttle is half open. 2.30V
4.4 Open the throttle to WOT and record the voltage. 3.88V
4.5 Slowly opening the throttle from closed to full open I observed that the sensor had no sudden gaps or jumps in the signal.
4.8 When the throttle is fully open, the VTA arm is at it's highest voltage due to the resistance being minimal. This voltage sohuld be around 5V. When the throttle is closed, or at idle, the resistance will be at it's greatest, which will decrease the voltage. This voltage with the car at idle will be around 0.5V
4.9 If the carbon track in the TPS was shorted or open circuit, the ECU will get the incorrect information to how far the throttle is pushed down. There may also be a poor connection to the ECU which will change the information that the ECU recieves.
ECT (Engine Coolant Temperature) sensor
6.3 Record the voltage from the ECT with the engine not running. 1.8V
6.4 If the voltage is 1.8V, I can determine that the engine is warm/cold
6.5 The voltage is good because my car has been sitting for about 10 mins.
6.7 This reading is lower then the voltage reading I measured when the engine was cold.
6.8 This tells me that this thermistor is a PTC type. As the temperature increases, the resistance increases, which lowers the voltage from the return wire. This information from the ECT gets registered by the ECU and the ECU can tell how hot or cold the engine is running.
6.9 When the ECU determines that the engine is cold, the ECU will try to add more fuel to try and warm the engine up. When the engine is running hot, The engine will try and lean off the fuel to try and cool down the engine.
Ground Coolant Temperature Sensor
7.4 Ground the ECT wire and record the voltage. 0.04V
7.5 If the connections were loose or the wires had become frayed there would be a poor connection to earth.
RPM Sensor or Crank Position Sensor
4.3 With the engine at idle, Attach a voltmeter to the RPM sensor and record the voltage on AC. 0.2V
4.5 Now with the engine started, measure the voltage on the voltmeter. 0.241V
4.6 Increasing the RPM to about 2500 I measured the voltage. 4V
4.8 Then I increased the RPM to 2500 again and measured the voltage, this time with DC. 19mv
4.9 Now I switched my meter to read Hz. With the engine at idle I recorded. 31Hz
4.10 Increasing the RPM to 2500, I measured again and recorded. 110Hz
4.11 I think the best way to measure that the sensor was working was the Hz setting.
4.12 I have a Inductive sensor on my engine. This sensor works by Magnets and coils spinning on CAM
4.13 A multimeter with Hz, AC,DC or even a RPM setting a great way to test a RPM sensor without use of an oscilloscope.
4.14 Loose connections, or a bad earth would give the ECU wrong information as to how fast the car is running.
MAP or MAF Sensor.
5.6 With my voltmeter on DC volts, I measured the voltage from the output wire when I turned the key on but engine off and recorded. 4.98V
5.8 Now with the engine at idle I recorded the voltage and got. 1.6V
5.9 Quickly stepping on and off the throttle I measured the increased reading on the meter and recorded. 2.45V
5.11 The above readings are correct for this engine because I have the specs for te MAP sensor and all tests conclude th the MAP sensor is in good condition.
5.12 If the ECU did not recieve information from the MAP sensor that the engine was under a increased load, the timing of the distributor would not advance.
IAT (Intake Air Temperature) Sensor
9.4 Record the voltage from the output wire. 1.91V
9.5 This reading is very close to what I recorded for my ECT voltage.The IAT sensor was only .1v more then the ECT sensor.
9.6 This sensor is also PTC. The resistance goes up as the temperature increases, which decreases the voltage.
9.7 The IAT sensor affects the ECU outputs for fuel injection by measuring the temperature of the air. The hotter the air is, the less dense it will be, so the ECU will counteract this by adding more fuel to try and compensate for the shortage of air.
9.8 The IAT sensor will have an decrease of voltage when the temperature increases for PTC sensors. And for NTC thermistors a voltage increase when the temperature increases.
9.9 If the IAT sensor fell out of the air box, and landed on the exhaust manifold for example, the sensor would tell the ECU that the air is getting very hot very quickly. The ECU may try to lean off the mixture when it's not needed to, and problems could occour. The wires could also fall out, this would give the ECU false information as to how hot or cold the air temperature is.
10.0 Camshaft Position Sensor (CMP)
10.3 Using a multimeter that could read DC and AC volts, Hz and duty cycle, I measured the different readings from the CMP return wire to the ECU and recorded.
DC Volts: 5-0.5V
Hz: 31-71
Duty Cycle: 10-100%
I think the best setting to measure the Camshaft Position Sensor was using the Hz setting. When we accelerated the reading went up and told us the frequency of revoloutions. When we decellerated the frequency went down. All other settings were fluctuating too much or wern't changing when we increased the throttle.
