MAP (analogue voltage) against Injector (petrol)
Signal Name - MAP / Injector
Volt/division/range - A 10v - B 2v
Time/division/range - 20ms
This test was done with engine idling. B channel is hooked up to MAP and has 2v divisions. A channel is hooked up to an injector and has 10v divisions. Point A on the photo is the voltage signal from the from the (MAP) manifold absolute pressure sensor. It is approx. 2v wile idling. Point B is the injector opening this is about 4ms the voltage is 0v because the injectors are earth triggered. Point C is the back EMF from when the injector closed this spikes at about 50v. Point D shows the injector closed it has 13v which is supply voltage and lasts for approx. 20ms.
Explain in detail how these two components relate to each other.
The MAP sensor measures intake manifold pressure and this is directly related to engine load. The voltage signal sent from the MAP sensor is used by the ECU which interprets any change in voltage as a change in pressure. This helps the ECU calculate how long to open the injectors in varying engine loads.
Ignition Primary / Injector :
Signal Name - Ignition Primary/Injector
Volt/division/range - A 50v B 20v
Time/division/range - 10ms
Channel B is the injector signal, at point A the injector opens for 4ms then at point B the injector closes and you can see the back EMF of approx 60v. Channel A is ignition primary you can see the coil is grounded about 5ms after the injectors opened at point C. Point D is the spark which is induced after the magnetic field collapses across the secondary windings of the coil. Point E is the current limiting of the primary circuit this stops the low impedance coil from over heating.
Explain in detail how these two components relate to each other.
Because the primary coil is the first part of stepping up the battery voltage for the spark needed for ignition the injector and the coil need to have very precise timing.
Oxygen Sensor / Injector :
Signal Name - Oxygen sensor/Injector
Volt/division/range - A 20v B 0.5v
Time/division/range - 1s
Channel B is the oxygen sensor point A is approx 0.1v this means air/fuel mix is lean and point B 0.3v meaning the air/fuel mix is richer. Channel A is the injector I couldn't get a very good pattern because of the 1s time division needed to see the oxygen sensor pattern, but you can still see where the injector is opening at point C when the voltage drops to 0v because they are earth triggered. Point D is the back EMF induced after the injector closes approx 50v.
Explain in detail how these two components relate to each other.
When the engine is warm and go's into closed loop operation the oxygen sensor will start cycling between slightly rich air/fuel mixture and slightly lean air/fuel mixture. This voltage signal from the oxygen sensor in part will be used to calculate how long the fuel injectors should be open.
Distributor G signal / Injector :
Signal Name - Distributor G signal/Injector
Volt/division/range A 20v B 2v
Time/division/range 20ms
Channel B is the distributor G signal which is an AC signal, point (A) is the peak voltage approx 3v this is when the air gap between the trigger and the magnet is smallest. Then the trigger moves away and the magnetic field collapses and a back EMF is induced this can be seen from point (A) down to point (B)
this is a negative voltage approx -3v.
Channel A is cylinder 1 fuel injector, point (C) is battery supply voltage 13v. Point (D) the injector is opened and because they are earth triggered the oscilloscope shows 0 volts at point (D). At point (E) the voltage spikes up to approx 40v this is caused by the injector closing.
Explain in detail how these two components relate to each other.
On this 4AFE engine the rpm sensor is in part used to determine injector timming and has no impact on spark timing.
