WS3A
we will check: MAP(analog); TPS(linear); ECT and IAT.
MAP:
Located right outside the intake manifold, it has a silicon ship in between a vacuum chamber and a pressure feed chamber from the intake manifold, usually a hose, so we can easily access this, without any difficulty. It uses ECU's reference voltage of 5V and a silicon/ Integrated Circuit so it will flex changing the resistance value as 5V comes by, giving low Volt signal when low pressure(idle) and high signal @ high pressure. For N/A cars, the highest manifold pressure is 1 atm.
There are normally 3 wires: PIM, Reference, and ground, we want the signal, so we need to back probe PIM to the oscilloscope. Maximum PIM is 3.68V, achieved by just disconnect the pressure feed hose from the intake manifold, the MAP will experience atmospheric pressure right away. @ Idle, PIM is 1.45V.
While 3.68V is not 2 bad for maximum pressure but 1.45V is quite high for idling. So despite the IC bit, the piezoresistive silicon chip pretty much a voltage divider circuit. So any corrosion or dust deposit can alter voltage distribution on PIM.
A high idle signal makes ECU gives more fuel even though there is actually less air intake => Car gets hot faster and stay hotter, richer, less fuel economic, components wear out more quickly. If signal is floating, sluggish idle will be experienced.
TPS and MAP are pretty much similar in purpose, so is MAF, because they all tell ECU about the load condition the engine is facing, so inorder to whether adding more fuel or run leaner. TPS is the most simple of all, you open the throttle and the graph goes high, let it stays idle 0.6V.
Faulty TPS gives bad throttle response. But this slightly affects ECU operation as it has all sort of air flow/ pressure sensor. Sluggish idle might be, but most important is the IDLE switch and Full open throttle switch that change the ECU's decision about how the engine operates.
ECT:
Variable resistor, heat sensitive, NTC type. So as the engine warms up, the signal is lowered to middle. As the engine stays cold, the signal is maximum. THis sensor can be found @ outside of any water jacket. Usually it has 2 wire, ground & signal. When testing this sensor, we have to wait for temperature change. There is another thermal fan switch which uses the same principal as ECT, but it's circuit closes after reaching a certain temperature, turning on the cooling fans on the radiator.
IAT:
Air under the bonnet is hot, not like air outside the car, but they are the same air. Anyway, when the weather gets colder or summer it is important to know because colder air has more density than hot air, but hot air is easier to ignite, take those 2 in mind they will affect combustion, performance, fuel economy and emission. IAT is pretty much like ECT, just a different range of resistance.
WS3
This section we check: RPM(magnetic crank or distributor) and Cam(Distributor)
Oxygen sensor
Oxygen sensor:
The second picture shows some snap accelerations, the O2 sensor is still responsive to fast, rich pulses of O2 changes, but then it goes really slow oscillation to find its way back to idle waves.
On a narrow band, 4 wires mean 2 wires for heater, 2 wires for signal, the heater wires are color identical, thus separates the signal wires.
The assessment purpose is to make us points out what is the signal behaving on the graph it makes, so we can interpret its operation based on theory. And this is important in diagnosis.
Crank signal
Volt div. 5V/ Time div. 1ms
Waves are smoothly identical, sine waves.
Frequency indicates how fast the crank shaft is spinning. From these signal, ECU knows the RPM and the crank shaft postion. The faster the speed, as we rev the engine up, the shorter the wavelength, thus higher frequency, and the greater the amplitude.
Cam signal on Distributor
Waves' shapes are identical to the rotor shape of the Cam sensor on the distributor; showing magnetic build-up and collapsing, continuously.
The higher the frequency, the greater the maximum amplitude.
There is a small gap every 3 waves indicating a reference point for 1st Cylinder in TDC of Compression, or simply missing a tooth, which I thing is non-sense because there is visually fine 4 teeth inside the distributor.
Injector
Volt 10/ Time 10ms
There is 4 period on an injector pattern: Off-0V
On(Pulse width)-~15-10V
Off-Voltage on switch solenoid discharge it self-~50-100V
Back to Off-0V
As we accelerate, we notice the increase in pulse width when there is an increase in RPM, plus greater voltage spike. Pulse width is the time the injector is held open, current natural built up inside the switch solenoid, then discharge as spike when the current is off, plunger is recoiled back.
Idle Air control:
Volt 10/ Time 10ms
We visual check the IAC device: Rotary solenoid IAC. But regardless on IAC types, duty controlled signal is always found in diagnosis, showing how much the IAC device is by-passing or restricting air.
@ IDLE: High bypassing percentage 60/40
Cold Idle: Very high 70/30
Cranking: Verylow 15/85
Acceleration: Low 30/70
Ignition Digital timing:
This is NOT the Ignition pattern.This is a shaped feed back signal from the IGnition module code name IGf to the ECU, to identify when and how long, how frequent the spark occur. Tracking this signal doesn't show us how the spark happens.
At IDle or lower speed, the spark occur slower, less frequent, less advanced, but last longer. This tells us that there is more time for dwell period.
Higher speed, more frequent sparks, but last less, given that there is less time for dwell period.
Ignition Primary
Volt 20/ Time 10ms
5 periods: OFF-Dwell-Fire-Burn time- Coil Oscillation and back to Off.
The faster the speed, the more frequent firing occur, but less Dwell time, less burn time, thus less firing voltage.
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