Magellan55

I used some STP fuel injector cleaner (yeah, not the best, but it's what the hardware store had when I thought of it) a few tanks ago, and my indicated mpg went from my normal 36-37 mpg to 38-39! I thought, great, glad I cleaned my engine which had been overdue. But after filling up again today I took the time to hand-calculate the mpg from those tanks, and was surprised to find that my mpg really hadn't changed - I'm still getting 35-36 by hand, just like before the treatment.

Anyone else notice this effect? I thought maybe the fuel injector cleaner would impact just the tank I used it on, but I've been seeing a higher indicated mpg for 3 tanks now.

Clutchless

I am confused, did it or did it not increase your mileage in your opinion?

If it is increased, that is because everything is cleaner now. That is how it is supposed to work. It cleans your fuel injectors and they work better for several months to a year until they gum up again and mileage drops. Then you run another bottle of cleaner. I recommend Chevron Techron or Redline fuel system cleaner as they have more of the most effective chemical whose name I forget.

However I would be surprised to see a mileage increase after running a bottle of cleaner unless things were really bad before hand. Usually it may just feel better, more responsive and smoother.

Magellan55

Sorry I wasn't clear. I don't think my actual mpg changed at all, as my hand calculations show it didn't. So I'm wondering why/how the fuel injector cleaner messed up my computer? Did it maybe do something to a sensor to throw it off so it thought I was using less gas? So far on this 4th tank, it's now indicating 37 mpg, which is a lot closer to normal for indicated mpg. so it appears the effect it had on my sensors is wearing off.

Clutchless

I do not think the cleaner can do anything directly to your computer. It affects the fuel system and engine, which had their operations modified by the cleaner while it was cleaning and this was different from the usual gas, thus your computer readings changed. The computer will re-adjust. I would not worry about it. Nothing you can do except spend more money and you won't learn much more. You could try a bottle of Techron and see what happens.