Acceleration Enrichment (AE)
coped from DIY EFI:
"What is it
The accel (acceleration) pump is used to add a bit of extra fuel the second the throttle is depressed, the harder, or rather faster you press it, the more fuel u will need to add, this is to stop the engine from missing from a sudden lean condition and the air rushes into the engine. Some will need more some will need less.
Tables you need
* Delta TPS = The initial value of fuel from the rate of tps or map change.
* Accel vs RPM = A scaler for the accel pump size based on rpm, you always need more at low engine speeds
* Coolant temp = A correction to the accel amount based on coolant temp
Settings you need
* Trigger = The delta rate that the accel pump engages. this will stop miss triggers
* Max size = The max amount of change that the accel pump will change the PW by.
* Decay time = How fast the pump will decay. this should be done as a percentage decrease based on the last value."
________________________
Another informative link about fueling logic for AE:
Acceleration Enrichment Fuel Tables
I will add:
Systems that use a MAP sensor also have logic that looks at delta-MAP (change in intake pressure) and uses an additional fueling table to add to the amount of fuel calculated for extra AE fuel delivery.
Older systems use the CTS (coolant temp) in determining a pulse-width multiplier in order to scale the amount of AE that was triggered by the delta-TPS, or the delta-MAP.
Newer systems use a bias table that blends the coolant and intake air temp to determine the scaling. When the engine coolant is cold, the table is biased more towards the coolant temp. When the coolant is at normal operating temp, the table biases towards the intake air temp.
YES, more throttle modulation will result in more fuel delivery, though it is very temporary.
There is a time-out function or "decay" of the added pulsewidth to phase the AE out over a time period and return back to running at 14.6:1 AFR (stoich). At a steady throttle your PCM will maintain 14.6:1 AFR no matter if you have +20% or -20% fuel trims.
However, if you have positive fuel trims at whatever load cell you happen to be driving in when you activate AE, those positive fuel trims are added in to the calculated AE pulsewidth, and that means more fuel consumption.
Negative fuel trims do NOT get applied to other fuel adders like AE.
Most experienced tuners like to shoot for very small negative fuel trims of around -2% in most load cells. That will keep your AFR from going overly rich under certain conditions like when AE or PE are being applied.
Intake air restriction CAN result in the need for increased delta-TPS, and YES that can trigger fuel enrichment more often if you're not careful. Modulating the throttle slowly will avoid this because the deta-TPS is calculated over time so a very slow change in throttle does not trigger AE.
When doing/testing pre-throttle air restrictions you have to keep in mind that your factory air ducting & filter are sized very close to WOT operation.
With your engine off, use your scangauge to read TPS %, use a screwdriver to hold your throttle open to the TPS% where you normally like to cruise, and then take a very close look at your throttle blade. Normally the blade will be barely open and you may have trouble seeing the small space between the blade and the throttle bore. This is a very small area for air to pass. This is more the scale that you want to think about when designing your air restriction. Otherwise the restriction will be way too large for you to be able to measure an increase in mileage using practical methods.
Start reducing the size of your restriction until you start noticing a difference, and remember to modulate the throttle slowly. This modification should be thought of more as a power-limiter, which keeps you from over-powering your engine so often during normal driving.
Also, don't expect much of a mpg gain just from restricting the air pre-throttle. To get a better gain, try to increase the resolution of your throttle control so that the same pedal movement results in less throttle movement. Then you will start getting gains that are easily measured.
Today
Other popular topics in this forum...
