TTEC4848 Vehicle Electronic Controls- blog 3

Oscilloscope Patterns to Capture

From this chapter we use the oscilloscope to test how does each components working when we use real car. 

Fuel Pressure and flow (Petrol only)

First we found the fuel pressure specifications of the engine is 265-304 KPa(2.7-3.1 Kgf/cm2,38-44 psi)
Than we checked from my engine the fuel pressure gauge and we haven't find any leaks from the fuel line. When we turn the key on engine off the record is 240Kpa, this mean the normal fuel pressure in the fuel line is 240Kpa for this engine. Than we did another test: Idling: 250Kpa; Maximum: with the engine idling, use the special tool to clamp the fuel return line the pressure is over 600Kpa and the engine was shake; WOT: we dis connect and plug the vacuum line when the engine idling, record pressure is 310Kpa; Residual: we turn off the engine and wait about five minutes we read the residual pressure is 270Kpa.
From this test I know the fuel pressure is very important of a vehicle, because every vehicle need the fuel, but the fuel need high pressure from fuel tank flow through the fuel line to injector. If the pressure lower would told to the ECU and ECU know the less fuel into the engine so the ECU will make the less air to mixture, than the vehicle cannot get enough power to running. But if high pressure will be waste the fuel because it is rich mixture.

Oxygen Sensor on Vehicle

I found the Oxygen sensor from the Exhaust manifold and it is an one wire type when we test the black wire I know this is an out put signal and also we know this is a Zirconia switching sensor. When we start the engine and we checked it by the oscilloscope, than we know the oxygen sensor connection is good. Even the engine warm up and we hold the rpm about 2500 we read the voltage wave from the oscilloscope and we can see the high voltage is 0.819V the low voltage is 0.169V, also we counts 7 times cross in 10 seconds. After we made the oxygen sensor goes to rich we just accelerating twice and very quickly and we can see the voltage goes up to 0.954V. Than we made it goes lean condition and we read the voltage is drop down to 0.045V.
From experiment we know the oxygen sensor is very important for the vehicle because it can give signal to the ECU how many fuel or air the vehicle need and how far the vehicle has, if the bad oxygen sensor can lose the fuel.

Exhaust Gas Analysis (Petrol only)

First we know the clean emissions should be at idle, when the car already warmed up is:

HC:        less than 100ppm

NOx:       less than 500ppm

O2:       less than 2%

CO2:       over      13%

CO:       less than 1%

We use the car is 1994 HONDA Integra.

           

1. We put the analyser probe sensing in normal air, we read the four gas is:
CO: 0% is mean not much CO in the normal air.
HC: 7ppm is mean not much unburnt fuel in the normal air
CO2: 0% is mean CO2 no much in the normal air
O2: 10.89% is mean in the normal air has very rich O2

2. When the engine start and in idling cold condition we record the four gas reading is CO: 0.73% HC: 471ppm CO2: 13.92% O2: 0.64%.
From this reading we know when the engine start the engine is cold so the unburnt fuel is higher so the HC is more than specification, but the other data is good.

3. when the engine has warmed up the reading is CO: 0.65% HC: 347ppm CO2: 13.54% O2: 1.7% λ:1.043

4. when the warm engine at 2500 RPM the reading is CO: 0.01% HC: 29ppm CO2: 14.93% O2: 0.17% λ: 1.007


5. at idle when we disconnect the MAP sensor we made the engine in rich mixture the reading is CO: 11.46% HC: 452ppm CO2: 7.77% O2: 0.23% λ: 0.737


6. at idle when we remove the PCV we made the engine in a lean condition with a vacuum leak and the reading is CO: 0.001% HC: 79ppm CO2: 12.77% O2: 3.20% λ: 1.168

From these experiment we know the emission test is good for check a vehicle running and the oxygen sensor also good for the engine mixture.