Mass Air Flow meter ( vane type)

Vane/flap type Air Flow Meter

The vane type airflow meter is diffrent to the hot wire type. This type has a mechanical moving vane/flap which moves in when there is air pressure. The vane moves in proportional to air flow and a voltage is sent out to the ecu in proportion to the distance the vane has moved.when flap opens the arm moves across a variable resistor. As the arm moves up and down along the resistor, the output signal voltage is changed which is sent back to the ecu.

With flap closed.

Flap wide open.

To do my experiment i connected my pinouts to the wiring diagram as above.5v reference at vc, 12 supply at Vb and earth at e2. Tha was the air temp signal. With vane close i got 4.48 volts and when i open it i got 1.4 volts.

Vane angle in degrees	Voltage
0	4.8
15	3.9
30	3.1
45	2.7
60	2.2
75	1.8
90	1.4

I couldnt check manufactures specifications as i dint know any part number or make and model of the sensor. To my knowledge is working fine as when we open the vane the voltage gradually decreases and increases as you relese the flap slowly.there is no break in the resistor.

Mass Air Flow Sensor

Manifold Air Flow Sensor (Hot Wire)

The maf sensor is located on the air intake after the air filter before the intake manifold.The mass air flow sensor sensors the amount of air drawn into the engine and sends a voltage to the ecu. A voltage is applied to the maf sensor to heat up the hot wire to about 100 degrees Celsius. The wires resistance increases as the temperature increases which allows less current to flow through the wire. when air passes through the maf sensor, it cools down the hot wire therefore resistance goes down and current flow increases getting the hot wire hot to its maintaining temperature. The amount of current required to get the hot wire back to its temperature is then converted by a chip in the maf to send signal voltage back to the ecu.

The hot wire has a self cleaning process. when the car is shut down, the hot wire heats up to about 1000 degress celsius to clean any dirt or grime stuck in the hot wire. If the hot wire gets contaminated and starts giving wrong readings there is no other way of fixing it then just to replace the piece.

without blowing air through maf.

blowing air though maf.

When i did the experiment i connected my bosch map sensor with the pinouts from the above table. i had to use to power supplies. A 5v and a 12V.without blowing air into the map i got 1.07v and when i blew air into it it increased to 2.2v.manufactures specifications tells us that the maf should have 0.5v at signal without air blowing thought it and out maf gave us 1.07. I think our maf is near to specification as we did the experiment in the class and there is a little bit of air flow as to the specifications are made to be done when the maf is connected to the intake and there is hardly any air flow when the engine is off. So i would say this maf is working properly.

Manifold Absolute Pressure Sensor / On car

Manifold Absolute Pressure Sensor

The map sensor is usually mounted on the firewall with a hose connected to the intake manifold.The map sensor is a very important sensor that sensors engine load. The sensor measures vacuum. More pressure is less vacuum and more vacuum is less pressure. At idle the vacuum is high as there is less air pressure in the engine. At open throttle there is more pressure therefore there is less vacuum in the intake manifold.

When i was testing my map sensor, i wired up a 5v supply and earth. Hooked up a multimeter to see the voltage at signal.I Then hooked up a mity-vac to the vaccum port of the map sensor. With no vacuum i got 4.8 volts at signal and as i applied vacuum with the mity-vac the voltage started to decrease. At around 70 cm Hg of vacuum the voltage got to almost .8v.

Vacuum cmHg	Voltage out
0	4.8
10	4.09
20	3.39
30	2.56
40	2.01
50	1.3
60	0.96
70	0.8

By my results its shows me that my map sensor is in good working condition and it is within the manufactures specification. My map sensor was a off a Toyota and i checked it with the toyota service manual that is posted on blackboard.

The map sensor reads vacuum to send out a voltage to the ecu. Theres is more vacuum at idle therefore its sends a low voltage telling the ecu theres less air in the inta`ke manifold. At wide open throttle there is less vacuum therefore the map sends a high voltage to the ecu. Its telling the ecu there is more pressure/air in the intake therefore the ecu adjusts injection timing and etc to give the engine optimum perfomance. 

On Car MAP Sensor

My engine had a map sensor. I back probed the signal wire of the map and connected my multimeter set to read DC volts. red probe to the signal and black probe ground. I turned the igniton on. I got a reading of 1.818V.

When i started the engine voltage dropped down to 0.541V.

When i revved the engine but just a short burst, the reading increased to 1.818v again.

When the ignition is turned the map reads the outside air pressure so we get 1.8v. As we start the engine at idle there is vacuum form the engine sucking in air so the voltage drops to 0.5v. When we are accelerating there is more air entering the intake, therefore more pressure and less vacuum so the voltage increases to 1.8 again. This voltage then tells the ecu that there is more air entering the intake so then the ecu increases the fuel into the air fuel mixture. This shows us that the readings we got was correct.

Problems that would send incorrect signal to the ecu from the MAP:

 - Vacuum leak in the intake

 - Leak on the map vacuum hose

 - The diaphram inside the map not holding vaccum.

 - poor grounding of the map ( high resistance on the ground)

 - Ecu grounding loose creating high resistance

 - corrosion on connectors

      

throttle position switch

Throttle Position Switch

 

This is the switch type tps sensor.This type only detects position at idle or at wide open throttle. This type uses contacts which work as switches. Switches are open or closes as the throttle position changes.

We did a resistance check with the tps switch to check if its working properly.We connected a multimeter on ohms to the idle pin and the ground pin and got a resistance o 0.3 ohms which told us that theres low resistance and good connectivity when the throttle was closed. As we opend the throttle a little bit to about 4 degrees the multimeter read OL. This meant that the switch was open now.

Now we connected the multimeter to the psw pin (wide open throttle. When the throttle was closed them meter read OL whcih meant the contacts were open. We started opening the throttle and to about 70 degrees of opening it read 0.4 ohms. This meant the switch was closed now and made connectivity. And the ohms ready told us that there is not a high resistance and connections are good.

throttle position sensor / on car

Throttle Position Sensor (Potentiometer Type)

There are 2 types of tps sensors which is the switch type and the potentiometer type, just by looking at the shape of this type of tps sensor we can tell its a potentiometer type as its has a round shape.Switch types generally have a square shape.

The tps is mounted on the throttle body connected to the butterfly of the throttle. As the throttle opens and closes the voltage changes which is sent to the ecu. The ecu uses this voltage to know where the throttle is at example if its at idle or full throttle to do calculations to have good performance of the engine.

Firstly to determine what terminals were which on our tps we did a resistnce check with our multimeter on ohms and looked at our circuit diagram to see what kind of resistance we would get when we open and  closed  throttle.There was no change from vc and e2 so we knew that   that was the power and ground.  Resistance decreased from vc and vta  as we open the throttle. Resistance increased for e2 and vta as we opened the throttle. By all this information we found out what terminals were what on our tps. 

Internal operation

Reference voltage to the tps is supplied by the ecu and the output signal voltage is changed by a internal variable resistor regarding the position of the throttle. Generally When the throttle is opened resistance steady decreases the the voltage at signal steady increases and reaches maximum reference voltage at wide open throttle.

Vc gets generally a 5v suppy form the ecu. There is a variable resistor at vc and a wiper arm is connected to vta (signal). As the throttle opens and closes the wiper arms moves up and down across the variable resistor. Vta is in parallel with vc and the voltage at vta goes back to the ecu. The magnitude of the voltage at vta is dependent on at which place the wiper arm touches the resistor. As the throttle opens the wiper arms gets more closer to vc so the resistance decreases between vc and vta and the voltage is higher at vta. The resistance increases between  vcc and vta when the throttle is closed therefore less voltage is at signal (vta). This is how the ecu determines the position of the throttle. As the throttle opens voltage increases at signal.

Throttle angle	Voltage Output
0	0.61
15	1.22
30	1.93
45	2.21
60	3.12
75	3.8
90	4.18

On Car Reference Voltage at TPS

We back probed the reference wire on the TPs and connected the red lead of our multimeter reading DC volts. The black lead was connected to the ground. We got a reading of 4.97V.


The purpose of the reference voltage is to give the TPS a reference from where the variable resistor will pick up voltage regarding the position of the throttle. A incorrect reference voltage will give out incorrect signal voltage out to the ecu. Thing that cause this are:
 - Bad regulator in the ecu that regulates the voltage.
 - Open circuit between the 5v supply and the TPS.
 - Frayed wires  causing a high resistance to supply full voltage from the ecu.
 - corrosion on connections.

Ground At TPS

To check the ground on the sensor we back probed the sensor ground and connected the multimeter red to the TPS ground and the black lead to the battery negative. We started the engine. We got 0.0mV reading.


This showed us that there is a very good grounding present as there is hardly any voltage drop from the TPS earth and the battery. Its important to check this to diagnose problems and to see if there is any resistance on the earth side causing a voltage drop. A bad connection form the battery terminal to the battery post can cause a bad earth. Bad connection from the ecu ground to chassis. Also from the TPS sensor ground to chassis being loose or corroded. resistance in the ground side will cause incorrect voltages at signal.

TPS Return / Output

To see the output of the tps we back probed the tps signal and connected a multimeter to read Dc volts. Red lead to the signal and the black lead to battery negative. With the ignition on we got a reading of 0.618V. As i opened the throttle the voltage incresed. To about half throttle i 2.676V. As i open the throttle more the voltage gradually increased. When i readed Wide open throttle the voltage was 3.93V.


When i oped the throttle from closed to open throttle there was no sudden voltage jumps or gaps in the signal. The voltage increased as i opened it. Our TPS was a 3pin.


The tps is connected to the throttle body with a wiper arm connected to the throttle butterfly.As the throttle opens and closes the wiper arms moves across the variable resistor on the reference voltage. The magnitude of the voltage at the signal is dependent on where the wiper arm touches the variable resistor. The ecu sends a DC 5V to the variable resistor to ground. As the throttle is opened the wiper arm moves more close to the supply side therefore less resistance is present and more voltage is at signal. When the throttle closes the wiper arm moves more close to the earth side, therefore more resistance is present making less voltage at signal.


If there is no reference voltage the signal would read 0. If the reference voltage has shorted to signal, signal would always read reference voltage.If the tps ground has an open circuit and wont let the reference voltage get to ground, signal would reference voltage all the time.If there is a high resistance at the earth, the signal will be higher than normal even at closed throttle.


The wiring diagram is above in the Off car part.