Fuel injector cleaning is a controversial topic. There are two main reasons for this. First, most Japanese manufacturers don’t recommend cleaning; they recommend replacing the injectors when they aren’t working properly. The other reason for the controversy is that most methods of cleaning fuel injectors don’t do anything other than generate profit for the shop performing the service.
“Fuel injector cleaning” can range from dumping a can of cleaner in the fuel tank, to connecting a machine to the car’s fuel rail to run concentrated cleaner through the injectors, to removing the injectors, flow testing, ultrasonic cleaning, then rechecking flow.
In my experience, if the car has an actual problem, such as an intermittent misfire due to poor flow or a poor spray pattern, adding injector cleaner to the tank or using a machine that add pressurized cleaner to the rail will do nothing to correct the issue.
I suppose there’s the possibility that regular cleaning with either of these two methods might prevent a problem from developing. As a guy who was selling a tool to “fix” bad hybrid batteries once told me, “This tool works much better on cars that don’t have a problem”. Do you know what else works well on cars that don’t have a problem? Doing nothing. There’s a line between preventative maintenance and “wallet flushing”. Almost all mechanics agree it exists, we just can’t agree on where it lies.
The cost of using a fuel rail type machine periodically would quickly equal the cost of just waiting for the injectors to clog and then replacing them, so there’s not really any value to to using a rail type machine as preventative maintenance. As far as adding injector cleaner to the fuel tank, virtually all gasoline already has cleaning agents to remove carbon from intake valves and injectors. I don’t think adding more cleaner will do much.
So if the in-tank and rail systems don’t work, what does? Ultrasonic cleaning works almost all the time. Ultrasonic cleaning requires removing the injectors from the car. On some cars this isn’t that much work, but on others it’s quite a project.
Since injectors can be difficult to remove and replace on some cars, and ultrasonic cleaning doesn’t work 100% of the time, testing is a key part of the process. Before cleaning the injector, we flow test it at a variety of pulse widths and frequencies to simulate its operation on the car.
There’s no way to test the flow rate against manufacturer’s specifications for a couple of reasons. First, the specification isn’t published in a service manual. Why would we need to know, right? We’re not supposed to be cleaning them! Second, injector flow testing is typically done with a calibration fluid that will closely match the characteristics of gasoline without the flammability. Without knowing the test conditions, fluid, and specifications, we can’t test just one injector.
Luckily cars have multiple injectors, and they’re all exactly the same. This means valid before and after testing can be done. If we flow test four injectors and the all flow different amounts of fuel, one or all of them is/are bad. If after cleaning they all flow the same amount, then the cleaning was successful.
Fuel injectors usually cost somewhere between $100 and $200 each. On a 6 cylinder car our customers can save a lot of money with cleaning vs. replacing.