not to stir old, but i agree with skishop. ghe just explained it better than i felt the need to. 90% of the cars on the road will see little to no benefit from injector cleaning solutions, unless they have actual physical dirt/grit that has made it past the fuel filter. the reason that solution was ever used in the first place is because it really works on carburetors. carburetors are a passive fuel system, where it is drawn via vacuum mostly, aside from accelerator pump circuits. in a fuel injection system, its pressurized anywhere from 20-60psi, simply the fact that its under pressure means systems can go decades without need for cleaning, as long as the fuel filter does not give way. the pressure blasts most soluble things right through without a hiccup. anything solid has the potential to clog and cause continuous leakage. the only way it will ever improve mileage is if the injector can no longer regulate fuel flow to what it was intended to deliver.
for example, say the fuel system is designed to flow 50lph. yours has a clogged filter, which cuts fuel flow in half. your car suffers from power loss, but is otherwise still driveable with a system that only flows 25 lph. even if the o2 reads lean, it can only enrich so much, especially with half of the intended fuel flow. in fact, no matter how much it enriches, it can only use 25lph. this case is just figurative, and the numbers pulled outta my butt, but the principle is the same. this lean condition wont help you pass emissions, but it does answer the question if cleaning will help mileage.
as far is spray pattern is concerned, its not really a concern with our motors, or really TBI cars for that matter, because the TBI system was based off starting the fuel by the throttle plate, like a carburetor, so that engine vacuum and a heated intake can assist in the full atomization of fuel. as far away as it is from the combustion process, the spray pattern could be and the driver wouldnt know unless he/she was extremely vigilant and noticed a single hp missing.
also, i might be new here, but im no stranger to cars. ive been responsible for a few spec miata motorsports race team successes, associates degrees in auto tech and hi-po engine building and tuning, working on a mechanical engineering degree. my own ea82 has a straight pipe, catless exhaust, and still passes emissions without any sneaky tricks thanks to a wideband o2 sensor and ported heads. im not new to this, thats for sure.
Edited by shadow, 26 February 2013 - 12:27 PM.