ttec 4848 #3

INPUT SENSORS & ACTUATORS

Injectors.

Injectors are an important component in the vehicle, it delivers the fuel at high pressure into the combustion chamber in an anatomized form ready for combustion, and it has to try and do this operation in milliseconds repeatedly. The length of time the injector can stay open is dependent on signals from other various sensors. eg. Throttle position sensor - When the driver increases the throttle he requires more fuel for power.

Above is a wiring diagram of an injector circuit. Ive used a mosfet which is in the micro controller to ground the injector circuit so when the signal from the micro controller comes in to ground the circuit, the injector will open and spray fuel into the combustion chamber. This operation occurs extremely fast.
If a problem occurred regarding injectors, this could result in misfiring, lack of engine power, excessive fuel consumption due to a leaking injector, bad emissions.
If a problem was occurring simple thing to do is check the battery voltage to the injectors because if their is no battery voltage to injectors then the injectors have no power to open and close or you check for resistance in the wires to the injectors because too much resistance could cause the injector to not fully open or close causing damage to the engine.

Reference voltage at TPS sensor

Using a pin i back probed the reference wire of a TPS sensor on a toyota corolla and got a 5volt reading on the multimeter. Which means that their is a 5volt reference voltage from the ECU to the sensor and it is their so it can receive a change in signal to the ECU to determine of it is opening or closing, If their was no reference voltage their will be no signal. The ECU creates this reference signal and not full battery voltage as battery voltage can vary depending the electrical load and this can alter the signal and send the incorrect signal back to ECU. If a problem occurred with the reference voltage this could mean that their is a corroded wire causing too much resistance or the TPS connector is damaged or the battery input to the ECU is low.

TPS GROUND

Using a multimeter i checked the the ground of the TPS and got a reading of 0.008volts which is a good reading, anything above 0.05 volts would show you have a bad ground to your circuit. It is important to measure the ground circuit to check if their is any resistance in the circuit as it could result in the ECU receiving the incorrect signal.

As the signal wire moves up and down the winding it will generate different voltage signals which sends it to the ECU and from their the ECU will adjust other things accordingly to match the demand of the TPS.

ENGINE COOLANT TEMPERATURE (ECT)

Using a multimeter I checked the ECT and with the engine on but not started i got a reading of 1.1volts but the engine was between cold and normal operating temperature.
I then started the engine and let it warm up for about 5minutes and when i checked the meter again i got a reading of 0.8volts  which was exactly the reading i was expecting.
As the engine heated up the resistance in the sensor decreased which showed in the drop in voltage. That indicated an Negative Temperature Co-efficient sensor.(NTC) resistance decreases as temperature increases.
The ECT  sensor is important in regards to fuel injection as the ECU gathers the information from the ECT sensor and it will adjust the air/fuel mixture according to the engine operating temperature, generally during cold starting or cold operating temperatures of the engine, the ECU will be notified it is cold so will enrich the air/fuel mixture. If the ECU received an incorrect voltage reading it could mean the earth to that circuit is bad or a corroded sensor and this could result in the ECU receiving a constant signal which tells the ECU its cold even at normal operating temperatures and will inject excessive fuel or could be opposite and tell the ECU it is constantly warm making it difficult to start in cold temperatures.

 SCAN TOOL DIAGNOSTICS

The above diagram is a picture of a similar scan tool (autoboss) i used to find specific vehicle data and information. This specific scan tool required a vehicle equipped with an OBD2 connecter so it can download this vehicle information.
Below is the link to the scan tool worksheet where i used the auto boss scan tool to gather different information.
http://moodle.unitec.ac.nz/file.php/1310/Practical/On_Car/Practical_Worksheets/WS5_Scan_tool_Diagnostics_Lab_Worksheet.pdf

for the Engine load i got a reading of 2.58 gm/s
Engine RPM - 705 Rpm's
Throttle angle - 10 %
Engine coolant temperature - 73 degrees Celsius
Intake Air Temperature - 25 degrees Celsius
Fuel Injection Opening Pulse - 2.7 ms
Oxygen sensor - 0.1v - 0.8v
Long term Fuel Trim - -14.8 %
Idle Air Control - 37.5 %
Air Conditioning condition - ON
Fuel Evap or Purge - OFF
Malfunction Indicator Light - ON

NOTE: some functions were not available on the scan tool so no information was provided for some components.
Using the Auto boss scan tool I then checked for fault codes to see if any faults were present and the scan tool showed no fault codes so i then had a colleague input a few faults to see if i could diagnose it with the scan tool.
When i re-scanned the system with the scan tool a fault code came up under the troubleshoot coding as P0120 Throttle position sensor. So i did a visual inspection and found the connector was loose. If this was occurring in engine in a vehicle this could be caused by an actual faulty or corroded connector which would require replacing. After connecting the TPS sensor and clearing the fault code on the scan tool and resetting the ECU by disconnecting the battery for 30 seconds. i noticed the engine was still idling rough and stalling at different times. So then i went back through the data information to check if anything had changed and it showed the long term fuel trim was at 0 % but the short term fuel trim was at a constant 19.5 % when it should be varying. So i looked to the Oxygen sensor and it showed a reading of constant 0v which indicated a fault with the oxygen sensor as it is not switching to lean or rich. This could mean the sensor is not grounded signaling to the ECU that it is a lean mixture and the short term fuel trim is trying to compensate for the air/fuel mixture causing the mixture to be more rich and creating high amounts of hydrocarbons.

WS3B

Map vs Injectors

The above diagram shows a waveform of a Manifold Absolute Pressure sensor and the injector circuit. The top waveform shows the opening and closing of the injector and bottom waveform shows the increase and decrease of the MAP sensor. Point "A" of the diagram is where is opened the throttle which shows an increase in voltage of the map sensor and increase in dwell period of the injector. As i released the throttle it shows in the wave form at point "B" in the decrease in voltage which means less pressure in the intake manifold and also point "B" of the injector shows a lower voltage spike and shorter dwell period ( the on-time of the injector.
So opening the throttle increased the Absolute pressure intake and increased the injector opening so it increases the fuel delivery.

RPM (crank position sensor) vs Injectors

 The above diagram shows the waveform of an injector which is the top waveform and crank position displayed as the bottom waveform at idle.

This diagram just like the one above it is of the same injector and crank position sensor. The oscillations in the crank position is much more frequent and the on time of the injector is increased by a large amount. This is because I'm running the engine at 3500 Rpm's. So opening the throttle will increase the speed of the crankshaft, at the same time will increase the dwell period of the injector.

Oxygen sensor vs Injectors

Injector waveform and oxygen sensor waveform.

 This diagram shows the oxygen sensor when it is in rich mode which means the injector should be putting out more fuel.

Injector pattern with o2 sensor waveform switching lean.

Again the using the same oxygen sensor and injector but this time tried to capture the o2sensor waveform as it switched to lean and check the reaction of the injector. Its not so clear but in when the o2 sensor reads lean the on time of the injector should be smaller as to when it is rich as it should be putting more air and less fuel.

EXHAUST GAS ANALYSIS

CO - Carbon Minoxide
HC - Hydrocarbons
CO2 - Carbon Dioxide
O2 - Oxygen
Nox - Oxides of Nitrogen

All the above are gases found in the exhaust, Depending on the air/fuel ratio and performance of the vehicle will produce either good or bad emissions.

Good clean emission readings:
•HC under 100 ppm (less is better)
•CO under 1.0 % (less is better)
•CO2 over 13 % (more is better)
•O2 under 2% (less is usually better)
•NOX under 500 ppm (on newer cars).
 The link below is for the above emission readings.
http://moodle.unitec.ac.nz/file.php/1310/Theory/Lesson_9_Emissions.pdf

Using an exhaust analyser I put the exhaust probe into the exhaust pipe of a Nissan Stagea to capture a few exhaust gas readings.
CO - !.187 Ppm
HC - 339 Ppm
CO2 - 13.55 %
02 - 1.24 %
Note; Catalytic converter was removed and engine was modified.
These readings were taken as the engine was idling cold but looking at the readings you could say their was a bad o2 sensor in this case.
The link above will show more good and bad emission examples.