Chart of inputs and outputs
Chart below shows measurements of sensors and actuators we have done in our lab with multimeter
Device | Measurement | Condition 1 | Condition 2 | Note |
Coolant Temperature Sensor | DC Volts | Cold Engine 2.6V | Warm Engine 1.07V | NTC warm engine should have lower reading |
TPS Key on | DC Volts | Fully Closed 0.691V | WOT 3.91V | Give a higher reading when open more |
TPS Key off | DC Volts | Fully Closed 0.72V | WOT 4.2V | With key on the reading is a bit higher |
Crank Sensor | DC Volts | Idle 4.07V | 2500rpm 7.52V | As speed increase gives higher reading |
Map Sensor | DC Volts | Idle Vacuum 0.54V | Key on engine off 1.79V | Higher pressure when stopped |
Air Temp Sensor | DC Volts | Cold Engine 3.46V | Warmed Up 3.2V | V decrease as temp goes up |
Cam Sensor | AC Volts Or Hz | Idle rpm 1.2V | 2500rpm 4.02V | Higher speed indicate higher voltage |
Fuel Injector | Duty Cycle | Idle 36.7% | 2500rpm 44% | High rpm indicate more fuel |
IAC | Duty Cycle | Idle 50% | 2500rpm 41% | High rpm less air bypass |
Sensors:
l ECT
l TPS
l CRANKSHAFT SENSOR
l MAP
l AT sensor
l CAM SENSOR
Actuator
l FUEL INJECTOR
l IAC
I have got some of the diagrams from the following web and books
Books
l Understanding automotive electronics 6th edition written by william B. Ribbens
l Automotive mechanics fundamental published by Gregory’s Publication
l Hand out from Unite
Internet Resources
http://ljet4826.blogspot.com/2010/09/coolant-temp-sensor-cts-thermistor.htmlECT
ECT Sensor | Cold Engine | Warm Engine |
Result | 2.6V dc | 1.07V dc |
Note
ECT – normally uses a NTC sensor which means as sensed temperature increases the voltage drop across the sensor decreases. This is because NTC sensor’s resistance decreases as temperature increase as shown in Figure1. We had 2.6V when engine start cold and it drops to 1.07V after engine warmed up. Our ECT sensor seems giving out a reasonable result.
TPS
TPS Key on | Fully Closed | WOT |
Result | 0.72V dc | 4.2V dc |
TPS Key off | Fully Closed | WOT |
0.691V dc | 3.91V dc |
The measurement we got shows that as the throttle valve opens up to WOT from closed this is due to the fact in the sensor there is a variable resitor which increases it resistance as throttle valve opens and decreases as it closes. When key is on will give a higher reading than when it is off
Crank sensor
Crank Sensor | Idle | 2500rpm |
Result | 4.07V ac | 7.52V ac |
As we can see that when engine is speeding up the voltage output of the sensor will be increased because the rate of change in the magnetic flux is increased therefore more voltage is developed.
MAP sensor
Map Sensor | Idle Vacuum | Key on engine off |
Result | 0.54V dc | 1.79V dc |
When the car is at idle the throttle valve is fully closed therefore there is a high vaccum which indicates low pressure. The sensor indicated this situation with a low voltage. Where as when engine is off, there will be no sucking action from the engine. Pressure inside is atmospheric pressure. That’s why map sensor indicated a higher voltage.
AT sensor
Air Temp Sensor | Cold Engine | Warmed Up |
Result | 3.46V dc | 3.2V dc |
This is also a type NTC sensor its resistance decrease as the temperature increase therefore it gives a higher reading when engine is cold and lower reading when engine is warm.
CAM sensor
| Cam Sensor | Idle rpm | 2500rpm |
| Result | 1.2V ac | 4.02V ac |
Cam sensor is basically very similar to a crankshaft sensor. It monitors the rpm and position of the pistons. As we have already seen with crankshaft sensor. This particular sensor is a magnetic type. As the tab move a crossing pole piece an alternating current is created in the sensor coil. The faster the camshaft turn the higher reading it will produce. Somehow crankshaft sensor will normally produce a much more reliable monitoring result because it is positioned next to the crankshaft.
Fuel Injector
| Fuel Injector | Idle | 2500rpm |
| Result | 36.7% duty cycle | 44% duty cycle |
In modern EFI system emission control and fuel efficiency are two main considerations. Control system will always try to stick to 14.7:1 air fuel ratio whenever is possible. It does this be adjust fuel injector opening and closing time. Duty cycle indicate what’s the percentage of time fuel injector will open or close up in a certain time. When the engine is at idle fuel injector only open about 36.7%, however as rpm increases it increased to 44%. Its control system’s job to decide what is the best duty cycle of a particular time is.
IAC sensor
| IAC | Idle | 2500rpm |
| Result | 50% duty cycle | 41% duty cycle |
IAC is measured in duty cycle similar to fuel injector. This measures how much bypassed air will be allowed into the intake manifold. When the engine is idling throttle valve is fully closed therefore IAC may need to bypass more air into the manifold to provide a smooth idling condition. As engine is out of the idling mode the throttle valve is opened up by driver bypassed air amount is reduced. Therefore its reduced from 50% to 41%.
