Coleroad

The first thing that happens is. The lighter fractions (such as pentane, iso-butane, toluene, etc) gradually evaporate off, which makes the resulting fuel blend harder to vaporize in the engine and ignite. Along with that the fuel oxidizes. This it when it gets darker and leaves a varnish. It also can erode certain parts. This from The anti-gumming additives being consumed over time, causing sedimentation as complex molecules slowly inter-react into heavier molecules. This is exacerbated by loss of lighter fractions, because they tend to be strong solvents and help keep contaminants dissolved. Going on along with all of this is Microbial digestion. (Yes, gasoline is somewhat biodegradable to specially-adapted organisms.). Storage, how long it sat in storage before you bought it, all plays a role it how long it takes to " go bad". Then you also have winter and summer formulations. This causes issues too if using one in the wrong season.

Coleroad

It only takes a very thin deposit to change the injector spray pattern. The spray pattern is very important for complete combustion. We are talking ten thousands of an inch will hinder the spray pattern. That's how close the tolerance at the tip of the fuel injectors. A photo that showed actual fuel injectors from one engine. None have a proper spray pattern. You can see how different each injector is spraying fuel. You can imagine how hard it is for the computer to keep a proper air fuel mixture.

Harold57

Thanks Coleroad, good explanation, great visual also (regarding the picture).

Coleroad

I'm all for premium fuel, and using add in fuel detergents. I use both to help maintain the car. It slows the deposits not stop them. Proper professional cleaning as the only sure fire way to clean the injectors when dirty.

Coleroad

With your air compressor and this tool just like the garage you can clean your injectors. Only a $120 for it. One use pays for it.
http://www.tooldiscounter.com/ItemDi...ookup=OTC7448A

Bgw70

And if you like to build things and have time on your hands you can build your own...