Errors that users may get when working with USB Autoscope

Wide open throttle not detected

Bad (Insufficient) filling of the cylinder…

The throttle was not fully opened

The standard practice for performing the Px test involves snap throttling. In this section, the maximum filling of the cylinder with a fresh air-fuel mixture is measured. The Px script displays the received data in the "Intake" tab. The diagram displayed in this tab allows you to assess the ability of the engine (more precisely, the cylinder being tested) to absorb fresh air when the throttle valve is fully open, and does not restrict air flow.

Why is it important? - Because the more air enters the cylinder, the more fuel will be injected, and the more power the engine will develop.

Now let's distract, take our minds off a little from the Px script and talk about measuring the maximum engine power. Dynamometers are used for this purpose. Such a stand allows you to measure the maximum power and torque developed on the wheels of the tested car. Moreover, they provide measured values not only as peak values, but also as graphs. Some of these stands are able to subtract the power loss in the vehicle's transmission from the measured power at the wheels, and thus calculate and display the power and torque at the engine crankshaft.

Now let's distract, take our minds off a little from the Px script and talk about measuring the maximum engine power. Dynamometers are used for this purpose. Such a stand allows you to measure the maximum power and torque developed on the wheels of the tested car. Moreover, they provide measured values not only as peak values, but also as graphs. Some of these stands are able to subtract the power loss in the vehicle's transmission from the measured power at the wheels, and thus calculate and display the power and torque at the engine crankshaft.

Now let's distract, take our minds off a little from the Px script and talk about measuring the maximum engine power. Dynamometers are used for this purpose. Such a stand allows you to measure the maximum power and torque developed on the wheels of the tested car. Moreover, they provide measured values not only as peak values, but also as graphs. Some of these stands are able to subtract the power loss in the vehicle's transmission from the measured power at the wheels, and thus calculate and display the power and torque at the engine crankshaft.

In such cases, you can perform the Px test again, while slightly changing the method: you need to turn off the engine as it is done during the CSS test so that the throttle valve is fully open during RPM drop. As a result, the filling of the cylinder can be assessed not only in the section of a snap acceleration of the engine, but also during a drop in engine speed after a snap throttling. To do this, during a snap throttling, when the engine speed has reached its maximum, it is necessary to turn off the fuel supply, and continue to hold the accelerator pedal pressed until the engine stops.

What may happen during a snap throttle, despite the driver's command the engine control unit does not open the throttle completely, maybe only halfway. Therefore, the engine RPMs do not rise as quickly as if the throttle was fully open; but still rise, and eventually reach the maximum.

Now the control unit sees that RPMs are already the maximum allowable, and further reduces the degree of opening the throttle valve, maybe only allowing quarter throttle.

At this moment it is necessary to turn off the fuel supply. The pump will stop supplying fuel from the tank, and the pressure in the fuel rail will begin to drop sharply, as the injectors will continue to consume fuel from the rail.

Due to the decrease in fuel pressure, the mixture in the cylinders will suddenly become so poor that the ignitions of the mixture in the cylinders will stop. As soon as the ignition in the cylinders stops, the engine speed will immediately begin to decrease.

In this case, the engine control unit sees that the driver continues to hold the accelerator pedal fully pressed, still requiring the engine to reach maximum speed. However, for reasons not understood by the control unit, the RPM is falling. To prevent the RPM drop, it begins to increase the throttle opening, and pretty soon the throttle is fully open. But, despite all the efforts of the control unit, the speed will continue to fall until the engine stops.

What will be the result? An additional red fragment of the diagram will appear in the "Intake" tab. This fragment will show the maximum filling of the cylinder at full throttle, not during the increase in engine speed, but during its fall.

Now about the methods how to stop the fuel supply during a snap throttle.

The easiest way to do this is by simply turning off the ignition.

But this method does not work on all cars, since the control unit can immediately completely close the throttle, deciding that the ignition off signal is more important than the signal of the accelerator pedal fully pressed by the driver.

If the first method did not work, then you will have to repeat the test. But this time, it will be necessary to turn off the engine not by turning off the ignition key, but by turning off the fuel supply. To do this, turn off the petrol pump located in the fuel tank using the Remote Power Off fuse switch. Before starting the test, it must be connected to the place of the fuel pump and during the test - at the moment when you need to turn off the engine, you must press the button on the body of the remote switch.

You can do without a remote fuse switch. In this case, you will need the help of an assistant. At the moment when it is necessary to turn off the engine, the assistant must either pull out the fuse of the electric fuel pump from its socket, or disconnect the electrical connector located on the gas tank, thereby turning off the fuel pump.