Here, we see four injector channels, while, the 3.0l V6 Jaguar engine has four valves per cylinder, 2 intake (2 injector-channels per valve), 2 exhaust. This injector comes with a coil resistance of 12 to 16 ohms and a >10 Mega ohm coil insulation resistance.

So, here we can see the polarity, of how this injector is connected in the circuitry. This injector is tide to a supply voltage >12v and is therefore negatively triggered.

So, here is my illustration of a home brew injector testing system, on the left side there is the pressure unit, which is a hand pump with an in and outlet valve. This hand pump comes with a piston diameter of 56mm and a maximum volume of 500ml. By using the formula p=F/A calculate the needed mass (kg) for the force N (weight here is water 1l=1kg, 1kg x 9,81m/s²= 9.81kg m/s²= 9.81N (1N=1kg*m/s²)) for the wanted pressure of 3 bars. If you don't have measuring cylinders use something likewise, with a 100g-200g weighing scale with 0.01g tolerances (10euro) measure the weight of each containment, note its weight, inject fluid to a maximal level, weigh each containment again, note its weight, subtract the containment weight. The weight of all fluids should be identical, if not, repeat the cleaning process again and again. If the cleaning process did not deliver the desired result, there is a big probability that the internal valve needle spring got weak and the valve stays open to long.

A spray pattern example.

Here's an injector, ignition coil driver. With this simple and powerful driver, you can create very high voltages when driving ignition coils or drive fuel injector coils at different duty cycles. The principle work scheme of this circuitry is that it works like a switching power supply. In this case the power distributed is not redistributed back to the circuit, though, it is regulated through the change of its period and impulse duration which in this case is contain in specific parameters and therefore separately adjustable. The main point of this circuit is its output-stage amplification, particularly the power transistor (IGBT). Through the very fast depreciation (500ns) of the primary voltage, there is a high and wide inductance, not only in the secondary windings but also in its primary, which can get very high when the spark gap gets longer and longer and then destroys the IGBT (1200V). Therefore the power transistor (IGBT) has to be held in its specific parameters. Its safety circuitry, here a Varistor (VAR1) which lets the higher than allowed peak voltages (IGBT HEF40106 shut-down about 500ns, 16A permanent power, 27A maximum, 1200V high-voltage proof) starting from 800V to 1100V be bypassed to minus.
How does it work?
The circuit connector X2 is fed with a voltage of +19V to +35V. Over the linear voltage regulator U1 we get a stabilized voltage of 15 volts, which is the best working parameter for this circiut. With the use of two CMOS Schmittrigers one of which is an HEF40106 that feeds the driver.
The first stage (IC1A) is a astable multivibrator which produces a periodic rectangular signal with an adjustable periodic time table of about 6ms to 46ms.
The second stage is a monostable multivibrator which produces an adjustable impulse of about 120us to 4ms period.
The main purpose of using a circuit like this is to keep the impulse period on the adjusted level when the frequency changes.
Timers like the 555 series impulse duration can't be adjusted when the frequency changes.
The rectangular wave signal drives a MOSFET IR211 (IC2). The MOSFET's purpose is to bring a clear and powerful drive signal to the output IGBT SPG07N120. The IGBT drives the ignition coil, whereby the coil is connected (X1) to +9V to +24V.

Important!
Experimenting with voltages can be very dangerous, if you are not inclined with electro-technique than don't experiment with this circuit.

Now you have completed your circuit and the High-voltage tension wire (4) is gaped to ground.

Start voltage = adjusted to 20V.
Period duration T = adjusted to its maximum.
Impuls duration t = adjusted to its minimum.
Oscilloscope voltage at R6.
Set spark-gap to about 5mm.
Power voltage = 12V (set laboratory power-supply to max. 2A)
Slowly prolong the Impuls-duration and keep an eye on your Amp-meter.
With an impulse-duration of about 200us a spark should occur.

Now, by (carefully!) adjusting voltage, period, impulse duration you can get some experience of how this circuit functions.

Note of caution
This driver is so strong, that the inner isolation of an ignition-coil can be permanently damaged, when the impulse energy is turn to high. Sparks of about 30mm (about 100KV at atmosphere) are achievable, dependent upon ignition-coil type. Most all ignition-coils die through shot-through insulation either internal or external and to a lesser extent shorted winding. When the spark encounters high, hot internal combustion pressure, the spark has to overcome a very high resistance (pressure, high combustion temperature, mixture lean or rich and some other odds) at its gap with a very high voltage at a very high speed. When the encountered resistance (spark-path ionization) is greater than the damaged insulation resistance of the ignition-coil, the very high voltage will always uses the easiest way to let part or all of its energy off, so a usable spark of about 30KV to 50KV can't be reached when the engine is under high stress. We have combustion pressures of about 10bar to 20bar. Ionizing an arc-path at atmosphere is easier then when it is in a chamber with a hot compressed fuel mixture in it. At atmosphere we need about 3.3KV/mm to ionize the spark-gap. A spark-gap in todays modern engines can be as wide as 1mm - 2mm. So, we can say that at 10bar combustion pressure and to ionize a spark-gap of 1mm we need about 5x the voltage at atmosphere. Than the insulating material, both windings and outer casing rapidly lose their high resistance, (cold 20°C >10GOhm to 50-100MOhm at 80°C) when temperature rises. So, what do we conclude out of this? Ignition-coils should be checked at their maximum allowable working temperature (data-sheet). If one or two coils are damaged, change them all, than the customer will comeback after a while with the same problem.

Here's an ultrasonic household cleaner with a custom made injector mount. This kind of cleaner has only one ultrasonic wave producer, which is directly mounted under the round molded cavity. This kind of unit will do the job to, though, it will need more time. All injectors have to be bound together and be placed directly over the ultra sonic unit (see clip).