Acceleration Enrichment tuning: There are a few that we have to consider. (Hang with me here) 1) You may remember from high school physics that water will boil at close to room temperature if you pull enough vacuum on it. Conversely, if you apply pressure you can raise the boiling temp up to 250F or more. 2) Water on the driveway always evaporated faster on a windy day than it does on a calm day. 3) Water on the driveway always evaporated faster on a hot day than it does on a cool day. 4) If you leave a cold glass of beer on the counter water droplets form on the side of the glass, apparently water from nowhere. 5) Cold air has more oxygen molecules per cubic foot that hot air. 6) A VE table as we in the MegaSquirt world is designed to balance the amount of fuel delivered from the injectors with the air flow. The internal math of the MegaSquirt estimates this airflow and in turn calculates the matching injector pulse width. This airflow calculation is based on intake air temperature, RPM, intake manifold absolute pressure (KPA), and RPM. 7) An intake manifold often has hot water in it. This manifold is attached to hot things and is being blown on by constantly changing amounts of hot air coming off of the radiator and from the exhaust system. 8 ) An intake manifold has a constantly changing amount of air properties and the amount of fuel that can condense on the walls. 9) Fuel in the intake constantly collects on the inside walls of the intake. 10) The amount (thickness) of this layer of fuel is constantly changing. 11) The earlier the fuel is injected in the intake airflow, the more area of the intake wall can get wet. 12) Back pressure on the exhaust, weather caused buy high atmospheric pressure at the end of the exhaust system or by trying to flow too much exhaust through the system causes the motor to need less fuel. 13) The injector delivers fuel only after it has opened. The injector opening time consists of about the first 1.0 millisecond of the pulse width. So if MT reports 10 ms pw1 the injector is only supplying fuel for about 9 ms. This is a big deal if you have a cruse PW of say 4ms and your AE added PW is 6ms. The amount of fuel delivered goes from (4-1) or 3ms of fuel to (4-1)+6 or 9ms or three times the fuel. Plenty of fuel to put out the fire. 14) Way too much fuel feels just like way too little fuel from the driver•s seat. 15) Fuel collecting in the walls and floor of the intake behaves much like the water examples above. A few definitions. MAP: Manifold air pressure. The units are KPA. The important part to remember is 100 KPA is close to amount of air the world has at sea level. At 6000 ft elevation you have 80% air or 80 KPA. 15 psi of boost amounts to about 200% air of 200 KPA. Most manifolds have on a steady state motor about 40 KPA at idle and 95 KPA at full throttle assuming normally aspirated. MAPDot: The calculation of the change of MAP/sec An indication of how fast the MAP is changing. Extra and base BG code uses KPA/Sec where MS2 uses percent/sec MAPDot is normally a better indication of a need for temperary additional fuel than TPS related schemes. TPSADC: The location of the Throttle Position Sensor as the Squirt sees it (0 = 0V ----- 255 = 5V). TPSdot: The rate of change of the TPSADC/Sec but converted on the display of MegaTune to Volts/sec the volts of the TPS go from about .5 volts at idle to about 4.5 volts at full throttle so 4 Volts/sec means the throttle is moving at a rate on going from no throttle to full throttle in one sec. MS2 works with percent/sec. AE driven fuel percent Gauge: This gauge displays the percent of added fuel taking into account the opening time of the injector. This little advertised is extremely valuable to put into perspective just how much fuel is being added at any given time. The opening time is assumed to be 1ms and is adjustable in the MsnsExtra.ini TPS Threshold: The value of the TPSdot that activates the AE event MAP Threshold: The value of the MAPDot that activates the AE event So how does all this pull together as it relates to tuning the motor? Remember that the VE table is designed to deliver the correct amount of fuel at steady state and normally will not be designed to cover for extra fuel required during these transition times in the fuel requirements caused by all these rules stated above. Any motor that is properly tuned to give a stable AFR at steady will have a huge demand for added fuel if the motor is exposed to more pressure in the intake. At low RPM the manifold MAP may jump from 45 KPA to 99 KPA in a very short amount of time. The added fuel is going to wetting the manifold up to the amount of fuel that can now coat it given the newfound pressure in the intake. Any time the opposite happens, fuel has to be pulled from the normal amount fuel required. This is referred to as the Decel setting. 90 is 90% of the normal amount of delivered fuel. The other 10% comes from the fuel that was on the walls of the intake and are now evaporating off the walls caused by the huge decrease in MAP pressure. At high RPM the motor may be running 90 kPa and a punch from ˝ throttle to full throttle may only raise the manifold MAP from 90 KPA to 95 KPA. This is a relatively small change in MAP and as such very little AE is required. As you can see from this MAPDot may be a better gauge of the required amount of added fuel. But what do you do if your cam makes it so that you have virtually no workable MAP change to work with and TPSdot does not seem to be a workable solution. What about this thing called decay and where do I ever start on tuning this thing. Over time, several ways to tune AE have evolved. 1) The original BG method: Based purely on the rate of change of the TPSdot or the MAPDot. The AE, once activated can remain on for a certain amount of time (or in some versions of code) for a number of ignition cycles. The advantage of engine cycles is that at 4000 RPM the AE time is ˝ of the amount of time that AE is active at 2000 RPM. The wider the power band and the more high strung the motor is the more difficult this method gets to tune both the high RPM and the low RPM requirements. ITB•s make this method almost useless. 5000 RPM v8s with an automatic is doable. All existing codes to date 2) The RPM based AE method: With this method, the RPM of the motor is constantly taken into account. Their 4 separate RPM values that can be set. Below the lowest RPM setting the max AE is controlled by the lowest ms cell. Between the lowest RPM cell and the highest RPM cell a linear interpolation happens between the two closest RPM cells. Above the highest RPM the highest RPM ms value is used. Only one threshold is in effect when using the AE scheme, depending on the choice of MAPDot or TPSdot. The AE table on the AE wizard is ignored. Note: This option is on Extra 026h8 and Extra 029M and later. All other versions have known issues. In addition to the accel enrichment bins, you also need to set the cold acceleration enrichments. These are the Cold Accel Enrichment (ms), and the Cold Accel Mult (%). Both of these affect the amount of enrichment when cold. overall pulse width = Req_Fuel * MAP * VE + (AE *CM + CA) + ... where: AE = acceleration enrichment pulsewidth CM = cold accel multiplier CA = cold accel additive Thus, the cold accel mult (%) a linear scalar for the acceleration enrichment that increases it by the specified percent, whereas the cold accel enrichment (ms) is an additive constant that does not depend on the accel bin settings at all. Both are linear functions of the coolant temperature (i.e. they have no effect at 160°F, 50% effect at 60°F, full effect at -40°F). In general, you need to set both for best driveability when cold. Try settings of 3.0 milliseconds for the Cold Accel Enrichment (ms), and 130% for the Cold Accel Mult (%) to begin. Adjust them to get the best overall driveability when the engine is warming-up. When you get it right you should be able to start the car up and drive away with any stumbles at all.