Due to how hot nameplates run their engines today for smog and gasoline for most vehicles have E10 or E15. Somewhat less allow for up to E85.
The combined of the 2 above plays hell with the fuel injectors and over time degrade and the owners of vehicles have no way of knowing if the injectors have degraded

Gasoline depending on the supplier that is adding cleaning agents may not be using the right types of enough of different cleaning agents.
People just assume what gas they are buying is correctly for the Ethanol and heat issues.

Another issue is the 2 O-Rings may also degrade and cause air leaks; the injectors may degrade and cause the injector to leak gas into the cylinders
Both issues then affect the proper AFR to 1 or both sides of engine and vehicle owner never knows the engine has lost performance or less fuel mileage
I had a sight imbalance of the LS1 of my C5.

I decided on doing this project to determine a good way to test fuel system for any type of leak and if the injectors were clean enough and working correctly
I also decided to see how cheaply I could put a test tool together to do what I wanted to test.

Figure 1 below shows the final design, with some parts I had lying around the total cost for this fuel system/ fuel injector test tool was under $75
There is injector cleaning products that depending on costs are supposed to do proper cleaning of fuel systems but most really cannot undo the degradation from the use of Ethanol

Below, Figure 5 shows four different fuel/injector products.

Some do very little and some are more costly and also are to do other cleaning as lubing the upper cylinders.
Best case and does not have to be done in short time frame is take the fuel injectors out

A cheap way, not the best is like $16 for a tool that simply hooks up to the vehicle battery and 1 injector at a time is plugged into this tool ( as seen below) and you need a cleaning product that is a spray where the nozzle of it is pulled into the tool, connect the voltage and push the nozzle top.
With the voltage to the injector allows it then to spray through the cleaner out the nozzle of injector.

I would not do this for a long time-frame as a injector is not designed to be on 100% of the time and doing so the internal coil of injector will get too hot .

Best case like in G.M vehicles is taking off 2 bolts on each side of the fuel rail, disconnecting the wiring connectors from each injector and removing the fuel line. Done in short time-frame

Being we want to test the fuel rail and injectors for air and fuel leaks tests I did:

1. With injectors still installed on fuel rail I choose to use a small tank (as below figure 1) that allows it to be put under pressure.
That is connected to the male stem on fuel rail.
Pumped tank to around 40 PSI. With no voltage to injectors they would be closed to any flow but receiving high air pressure from tank.
I let that sit for 24 hours and via a pressure gauge could tell there was a slight leak in testing of :

A. Any part of fuel rail parts
B. A stuck open fuel injector
C. But did track down one O-ring causing a pressure leak.
Once replacing that repeated the pressure test for another 24 hours and no drop of pressure found.
D. That testing gave insurance anything part of fuel rail was fine now with the replacement of that 1 O-ring

2. Next test was to replace the pressurized air in the test tank with cleaning product.
3. To do this as seen below I built a system where I could test from 1 to 8 fuel injectors one at a time or multi ones concurrently.
Your setup does not need all I did but you want a way to flush each injector with cleaner and be able to see

A. If the spray holes of injector are clean
B. That the spray pattern on each look the same.
C. Could go so far as to allow cleaner to spray through a injector into a small container that measures the amount cleaner sprayed in X amount of time.
Such as if the injectors are rated to flow 55 CC a minute then allow your test to run that long and then see if the container measurement shows that amount of volume
D. If not then assume the nozzle holes are partly plugged up and require more cleaning time

1. As mentioned the internal coil of injector was not designed to be on 100% of the time as that would overheat that coil
2. The engine management controller commands how long the injector will flow but in short milliseconds of time.
As example at idle the PCM may command injectors to be on for 3 mS and then turn off. Maybe at part throttle command is 20 mS
3. This is called “Fuel Injector pulse width ON time”
4. So for our testing we needed to add a Pulse width controller that allows for a more real pulse on times. The one I used is set as reported below
5. Partly filled the pressure tank with a good know fuel injector cleaner

6. Did not want to spray/clean all 8 at the same time, I wanted control of each one
7. Did so by getting 8 single pole switches costing only $7 dollars for all 8
8. Bought 8 fuel injector wiring connectors that have shot pigtail wires and also installed a power switch, used a D/C power unit and a NODE you can buy that is a LED that would show the output pulses of the controller.
A. With the cleaner in tank I pressurized it to around 40 PSI.
B. Now I could turn on switch for 1 injector, watched the cleaner flow through it and looked at what the spray pattern looks liked. See figure 2
C. I then turned that switch off and repeated for the other 7 injectors while watching their spray patterns and assured there was still enough cleaner in tank and the pressure did not get too low.

D. Last test is I turned on for short timeframe all 8 switches so all injectors were flowing
E. Shut off all switches and then watched for around 15 minutes with injectors OFF and still cleaner in fuel rails and tank still under pressure if any injector was leaking cleaner out showing a internal injector leak
F. Review figures 4 and 5 as to spray pattern seen.

Once test tool was built which can be used many times, the cleaning process alone only takes about 20 minutes and you then end up knowing the better conditions of injectors or you found leaks, or injectors too degraded and need to be replaced.

Explanations for the 4 Modes of the Injector Pulse Controller

Mode1: the tester will output 1 pulse, whose pulse width is about 250ms.

Mode 2: the tester will output 50 pulses; every pulse’s pulse width is about 7ms.
Mode 3: the tester will output 100 pulses; every pulse’s pulse width is about 3.5ms.
Mode 4: the tester will output continuously at the rate of 50 pulses per about 1450ms, every pulse’s pulse width is about 7ms.

The tester can help diagnose injector problems;

You can use it to test each injector individually to help identify stuck, leaking or burnt-out conditions.
It uses 12V vehicle battery or power supply for D/C power.
It has 4 pulse modes;
The continuous mode (mode 4) helps identify good or bad injector.
The mode lock feature ensures test condition uniformity.
It can work with any fuel pressure tester.