[mgarblik]

Originally Posted by KS circutguy

They can still be partially clogged and still run decent.
Just not as good as clean, the spray pattern won't be optimum.
Not worth the risk. imo
Also keeping fuel filter serviced is of upmost important nowadays.

At my school, we have 2 fuel injector test stands much like that picture. We have tested hundreds of injectors with this unit. The primary take away for me is: The injectors can have ANY of the spray patterns pictured and the engine will still "run and feel fine" to 95% of the drivers out there in their daily drivers. Only someone who is extremely "tuned-in" to exactly how their car runs will notice the difference unless the injector is clogged to the point where little to no fuel flows out. My statement applies to PORT injected engines, not direct injected engines. This is because the warm intake tract still gives the cylinder time to heat and vaporize at least some of the injected fuel, even if not atomized properly. You may notice a small decrease in fuel mileage as well with a lousy spray pattern and the all too familiar "poor catalyst efficiency codes".

A direct injected engine however is more likely to run poorly if clogged because there is a greater chance of liquid fuel droplets to make it inside the cylinder. These issues start to show up just after the warranty expires. Around 60K miles. Top tier fuel, and/or an occasional bottle of Techron or similar cleaner probably isn't a bad idea. Once a fuel injector gets bad enough to really feel while driving, no chemical cleaners will fix them in my experience without removal.