So if I never reset the ECU after a modification, does that mean that I might not get the full advantage of a particular mod?

I did some recent intake modifications with the upper section of the CAI -- an increase in torque from 2500-3500 RPMs was noticed pretty immediately -- so I didn't think I had to do anything with the ECU --

If I don't reset the ECU, does it mess up the appropriate fuel mixtures that would go along with each intake mod? I used to get like 19MPG city consistently for as long as I have owned the car since 1995 -- but lately, I can't hope for much above 16MPG -- I don't really drive any differently than before --

But I've been thinking about the posts about the car stereos sucking up gas -- there could be a correlation there -- I did recently get an Alpine amp with 750RMS total watts
Considering that class A amps are about 25% efficient (if I recall correctly) plus other system losses, I'd say that sucks up about 5-7HP -- 5-7HP at about 2500RPMs cruising speed requires about 10-15LB.FT of torque -- and that is approaching about 10% of the engine's available torque --

I got a TECHTOM device where I can read my fuel injector and MAF data -- I could just sit in the car and cycle the stereo volume up and down while cruising and see if I can quantify a difference ...


I saw Brian V's post and instructions about resetting the ECU -- I've never done that to my ECU before -- I'll try it and see what happens --

 

No. You might not get the full benefit right away. However, you might not get the full benefit immediately even if you do reset the Engine Control Module.

IMHO this business of ECM "learning" is exaggerated. It is true that the ECM establishes a Short Term Fuel Trim and a Long Term Fuel Trim as mileage increases. It is true that some mods may yield best results with a STFT and LTFT different from what evolved with the stock engine. However, the ECM will continue to adjust as you drive.

You may think of the fuel trims as similar to the bass and treble adjustments on a radio. There is a mid-point, and you are free to adjust each control higher or lower to suit your listening preferences. Resetting the ECM merely resets that "bass" and "treble" to the mid-points again. There is no certainty that the mid-point is better suited to your new mods than just leaving everything alone.

 

There are a lot of reasons for increased fuel usage.

Gasohol.
Did you formerly buy gasoline and are now fueling with gasohol? Gasohol does not deliver as many mpg as straight gasoline.

Oxygen Sensors.
These deteriorate with mileage and become "tired". Tired sensors won't trigger the Malfunction Indicator Lamp because they are still working (but not well). Tired sensors may be noticed by these symptoms:
- increased fuel consumption
- decreased engine power
- loss of the crisp throttle response the car had when new

Normal wear.
Even with meticulous maintenance an engine with 100K miles on the clock can't have engine valves and piston rings that seal as well as when new. Normal wear causes a loss of fuel efficiency.

Dirty or sticking fuel injectors.
Injectors deliver the fuel in the form of a spray of tiny droplets in a dispersed pattern. Injectors which are not operating perfectly produce a malformed spray which does not facilitate optimum combustion. Injector cleaner may help.

Obstructed exhaust.
The Catalytic Converter accumulates an ashy residue as a normal consequence of operation. At some point enough of this garbage builds up to have harmful effects.
- the car fails a smog test
- the exhaust system develops excessive back pressure which detracts from engine performance and fuel efficiency