Techron is good stuff, but only the bottle marked "synthetic concentrate" is strong enough to have any real effect over 15 (+/-) gallons worth of gas (about how much one 12 oz. bottle of Techron synthetic concentrate is designed to treat).
GM repackages Techron Concentrate under their part numbers for dealership use when treating engines under warranty that are sensitive to injector clogging, intake valve deposit buildup and combustion chamber deposit build up. During my studies getting my car degree from GM we did a pretreatment teardown of a higher mileage engine with pretty nasty carbon deposits in the combustion chambers, intake valve deposits and restricted injectors, then put it back together and dropped it in the car, running two tanks of fully treated fuel through it (~24 gal total). We then tore the engine down again and took a look at the intake valves, piston tops and ran a spray bar injector test for pattern and a CC test for flow.
Bottom line, Techron concentrate works pretty well. It notably improved the injector pattern and flow (but did not make it like new). It removed considerable deposits from the combustion chambers, down to clean metal on the intake valve side and somewhat less on the exhaust valve side. It removed most but not all intake valve deposits. Note that this engine was a severe example, having been run for 60,000 miles on the cheapest fuel available. It pinged on regular and idled poorly (failed an emissions test too) before cleaning. After treatment, it passed emissions, idled a lot better, and ran on regular as it was designed to do. It did take two full tanks of treated fuel to accomplish this improvement.
Of course, if you have clean injectors, no intake valve deposits, and clean combustion chambers you don't need it.
The Top Tier gas site has some good info on the tests and better standards encouraged by participating manufacturers (BMW, General Motors, Honda, VW, Audi and Toyota) and why the current, weak US federal standards are inadequate to prevent deposit formation in those critical areas.
See:
http://www.toptiergas.com/deposit_control.html for more info.
GM Top Engine Cleaner is particularly effective for direct application to piston tops, intake valves etc (pour in and let sit). It will get rid of ALL combustion chamber deposits and intake valve deposits but application is more labor intensive and a bit tricky. IIRC T.E.C. has been superceded by something less toxic (TEC used a witch's brew of nasty toxic solvents that worked like gangbusters but was pretty poisonous, like 9-octadecendic acid, 4-methyl-2-pentatol and 2-butoxyethanol). TEC was not intended to be poured in the tank.
I use one bottle of Techron concentrate (6 bucks on sale) every 20,000 miles or so in my car and my bike as a preventative measure since I tend to use the cheapest gas I can find. It works well - my Civic has 181,000 miles and runs like a top, the Sprint has 56,500 miles and runs well too.
If you have used top tier gas since new, chances are you'll have no need for Techron or any other fuel additive.
