witmeraa,
Congratulations! It sounds like you've built yourself a nice system. But, there is always a but, there are a couple of suggestions I'd like to make.
First, you say you can see the HHO streaming out of the hose going to your engine, but are certain it isn't steam. You are right in that it probably isn't steam. But what you are seeing is water vapor carrying with it whatever corrosive electrolyte you are using. This water vapor is caused by the mechanical agitation of the electrolyte inside the cell. It can't be avoided, but you do need to take measures to remove the NaOH from this water vapor before it enters your throttle body, because it will cause damage to it over time.
We do this with a separate bubbler/scrubber. Search the forum and you should find lots of good information about this device.
Secondly, about your check engine light and MPG. I do not consider what your seeing to be unusual. I just installed a system on a 2005 Kia Spectra with a 2 liter engine. I started with straight HHO and ran it at several levels, even going as high as 2.5 lpm in one test, and never threw and check engine light -- never saw any MPG improvements, either. I then installed a volo performance chip and repeated the same test and got the same results. I have recently unhooked the volo and installed a conventional EFIE. While tuning the efie, I at one point had it so lean that when I pulled onto the interstate the engine died at 60 MPH -- and I still wasn't showing a check engine light. (and it is does light when I start the engine so I know the light bulb is good, and scan gauge doesn't show any error codes). Fortunately I am starting to see some MPG gains and am currently looking for the sweet spot as far as lpm go.
So, I guess my point here is that while some vehicles easily through a check engine light with HHO, some don't.
Sorry for the length of this message, I don't have time to make it short.
Steve
1991 Plymouth Acclaim 3L V6.
1 dry cells with nineteen 6"x8" 316L ss plates, driven by constant current PWM set at 35 amps (13.3V at PWM). 28% KOH electrolyte. Total measured output 2.5 lpm. Mileage went from 18 to 26 mpg, all city driving (44% increase). EFIE set at .370 and I still need to play with ignition timing.