There's no one-way valve in the injector. They're just pintle valves... much like a spray gun. Other cleaning methods will remove soft deposits, such as wax and varnish. But if there are hard particles in the system, reverse flushing will (hopefully) move them back the same path they came from, out the inlet.

I got the idea from reading the info from on-line injector cleaning services. They too use ultrasonics and reverse flushing. They also check the flow balance among the injectors to make sure each set flows the same amount.

The beauty of tvpierce's setup is that - if done carefully - one can use this to check the injectors for flowrate and perhaps identify an oddball. Then you've done everything a professional cleaning service can do.

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95 E320 Cabriolet, 159K