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I dyno'd my S2K today and although the numbers looked good (196.1 HP, 131.7 ft/lbs) I am concerned with the Air/Fuel ratio (see graph below) The A/F ratio starts off at 18:1 and 14.7:1 for airbox cover off and cover on respectively, But after that, the A/F ratio drops to 12:1. Is the 12:1 ratio normal or is the engine starving for air? Has anyone else dyno'd their car and gotten similar results?
No, the car is not "starving for air". All this means is that it's running "rich". The ECU is correctly putting in enough fuel at higher RPMs to be safe. The numbers look perfect...it's exactly how it should be. Your car is not lessening the air it's getting as it goes along the RPM range, it's just increasing the ratio of fuel...adding more fuel per unit of air. Does that make sense?
The airbox cover off is the blue line (hard to tell the color, I know) The HP and Torque curves are nearly identical, but the a/f ratio curves are noticably different.
I think all you're seeing is the ECU working with the MAP to compensate for the hotter / more humid air that was being brought in without the air box cover on. Technically, a car can run leaner in humid conditions than in dry conditions. It looks to me like the ECU had to lean out the midrange just to make the same power...and then went to the safe 12.0 at the higher RPMs.
09-07-2002, 07:10 PM
Air/Fuel Ratio seems off
