Circuit Test
When turning the ignition key to ON (connected to) the location, you can hear the PCM (pulse control modulation) briefly connected to fuel pumps. If the engine does not start, for security reasons, PCM will re-close the fuel pump a few seconds. When turning the ignition key to the START (starting) position and turned back to ON position, PCM will rely on the crank position sensor to determine whether the engine is running.
The assumption that when you will be connected to the location of turning the ignition key, he did not hear the fuel pump running, then at least the following three reasons that can cause fuel pump does not work.
For some reason, PCM decided not connected to the fuel pump;
PCM and the fuel pump in between, there is failure;
Fuel pump was actually connected, but not functioning.
We will rule out the two obvious choices. PCM is the assumption that fuel pump relay commands access and electricity, and assuming the fuel pump itself intact, is the PCM between the fuel pump and a reason to make fuel pump can not operate normally.
Will DMM (digital multimeter) to connect the fuel pump of positive and negative terminal, then turning the ignition key to the ON position. DMM should immediately read out the battery voltage. If not, then find in the fuel pump and relay whether there somewhere between the open circuit. In addition, the relay itself, there may be failure.
If the fuel pump in the state electricity and grounding, fuel pump to determine whether or not to receive a sufficient number of electrical energy. As the fuel pump low-impedance, DMM can be pointed out that the location of fuel pump in the battery voltage. But the drop test can be revealed: In the circuit load, the actual voltage to the fuel pump in the end how much lower than the battery voltage.
To the entire fuel pump circuit voltage drop test, the circuit should be divided into two halves: first, the grounding side of the circuit; then the positive side of the circuit. All tests have to be in the circuit manner. The use of fuse jumper to give the fuel pump and fuel pump relay circuit electricity.
Electricity in the circuit, it will be a DMM test leads to connect the negative battery terminal, will be another DMM root fuel pump test lead to connect the negative terminal. If the grounding circuit normal, DMM should indicate about a drop of around 0.1V. If greater than the pressure drop, have shown that arrived in the fuel pump voltage before a loss of voltage. Damaged or corroded wires or wiring harness connector, it could lead to the occurrence of this phenomenon.
If the grounding side of the circuit voltage drop detection finished, and drop no problem, then the positive side of the circuit voltage drop test is repeated. Will be a DMM probe placed in the fuel pump relay output terminal will be another DMM probe placed in the fuel pump on the positive terminal. If the pressure drop DMM shows greater than 0.1V, then find the damaged or corroded wires or wiring harness connector.
The use of "half-and-half hours" method to determine the location of fault lines. First, the circuit is divided into two halves, and then, in the circuit as well as between the central and relay circuit between the central and the fuel pump, repeated pressure drop test. This allows you to identify the fault occurred in the first half of the circuit or the second half. If the circuit the latter part of the larger drop, the latter part of the circuit will be further divided into two halves, each drop test. Each circuit is divided into two and a half years, found fault on the distance getting closer and closer to you.
Figure 1 shows the beam joints conducted online drop test, the two probes were placed in the joints on both sides. DMM display the pressure drop of only 0.006V, completely acceptable range.
Keep in mind that in the supply voltage to reduce the circumstances, do not expect fuel pump can operate normally. Next, we will explain how to use the low current probe and DSO (digital storage oscilloscope) to detect and diagnose fuel pump internal "health" situation.
Current Test
Inductive current probe a variety of shapes and sizes, can be used to test the size of the AC current and DC current. Inductive low current probe that can be used to measure the fuel pump circuit low current (typically 10A below).
Inductive probe, the signal will be measured into a voltage can be read out of the DSO (digital storage oscilloscope) the identification signal. Although the DSO (digital storage oscilloscope) show that the voltage signal, but we know they actually represent the current.
Most low-inductive current probe has two stalls - 10mV / A and 100mV / A, their impact on digital storage oscilloscope waveform display on the screen. If the inductive low current probe was adjusted to 10mV / A stall on, corresponds to the digital storage oscilloscope shown each 10mV / A, probe is a measure of the current 1A. If the inductive low current probe was adjusted to 100mV / A of the stalls, the corresponds to the digital storage oscilloscope shown each 100mV / A, probe is a measure of the current 1A.
Digital Storage Oscilloscope watching the fuel pump current waveform from each sub-degree 1ms or 2ms time coordinates and each sub-degree 100mV voltage coordinates the beginning. 1ms degrees in each of the cases, able to form a more detailed analysis; and in each sub-degree 2ms circumstances, can be relatively easy to calculate the speed of fuel pump.
Folder in the probe into the fuel pump wiring before the oscilloscope and the probe was adjusted to these settings, and then, using inductive probe ZERO (zero) regulator control panel, will be adjusted to the wave of digital storage oscilloscope 0 ( Earthing) location.
Current probe clamp on the fuel pump circuit can be any location, as long as it is in tandem with the ground between the power supply line. Folder to probe into the fuel pump wiring on one (if you have enough to get any), or folder to the fuel pump in the fuse box, relay switch or inertia switch the location of the power line, or a folder located in the engine cover the following Detection connector.
Although the circuit within the voltage difference may be different, but in the series circuit, all points of the current is the same. Therefore, in order to ensure that no other parts (for example, pump) in parallel circuits in the main pump, this is because of these components will affect the test results.
In the detection of fuel pump when the engine and other electronic components must not be in working order, they will affect the functioning of the role of the fuel pump on the voltage, but also will affect current readings. Some manufacturers in the hood of the following provides an independent joint-lead detection for power supply to the fuel pump. In the engine in the OFF state so that the fuel pump to draw support from the detection of joint operations, will be connected to a power jumper connector on the detection.
Before using this method, we must view the route map. In the fuel pump power is provided through external wiring, you can bypass the fuses, relays or other switch components. If this is the case, in the lead during testing, pump current display may be within the scope of technical requirements. However, in the normal work of the vehicle, the bypass circuit voltage drop may result in lower pump current. Ideally, in the detection of fuel pump, the fuel pump power supply wiring should be with vehicles during the normal work of the same power supply wiring.
Good fuel pump, it will produce a similar Figure 2 shows the characteristic curves. Oscilloscopes was set up in each sub-degree 100mV, probe is set at 100mA / V. Degree equivalent to a vertical 1A, thus, pump current is between 5 ~ 6A.
In the fuel pump in good condition, the waveform of the peak should be consistent. Brush with one or more for the poor contact between the chip will lead to uneven peak or low-amplitude peak.
Mechanical fuel pump inside the pump current resistance will cause higher than the normal average pump current. Blocked fuel filter or pipeline may also result in increased pump current. Inside the fuel pump or other location-circuit resistance, would reduce the role of the fuel pump voltage, thereby, reduce the pump current.
