The ME system uses two methods of AE. You can use either the Manifold Absolute Pressure (MAP) or the Throttle Position Sensor (TPS) to calculate the rate-of-change, or ‘Delta’ of the throttle plate. Note that MAP based AE is ‘ok’ but for the best drive-ability, TPS based AE is preferred, and in any cases vehicles not fitted with a TPS will lose out on other ECU features, so it is always recommended to fit a linear TPS sensor. Please read the section on ‘Throttle Sensor Calibration’.

The following tab layout is recommended to carry out AE tuning, and it assumes that the VE table under steady state is mapped correctly, and the engine is warm.

You will need the following widgets open:

●        Acc. Enrich Driver

●        Acc. Enrich RPM Clamp Trim (table)

●        PW Table Acc Delta Enrich (Table)

●        RPM, TPS%, Acceleration Delta, ACc Enrich VE Add (%), Total VE (%), Injection Pulsewidth DROs

Before we cover tuning the AE, the theory needs to be covered:

Acceleration enrichment (AE) is used in a fashion like ‘pump jets’ on carbs - it is designed to enrich the fuel as the throttle is opened, to compensate ‘in advance’ of the drying of the intake manifold, and the increase in airflow, before the VE map takes over and provides steady state fuelling.

Firstly, we must tell the ECU which type of source we will use to calculate the Accelerator Delta (its rate of change) either MAP, or TPS. We always advise using TPS when possible.

Now the ECU needs to know when it should enter acceleration enrichment, and this is configured in the Accel Driver via the ‘deadband(%/s)’ setting.

With the engine idling, or under general driving, take a note of the Accelerator Delta DRO, (a data log may be easier for on road testing) and in steady state conditions, it may still fluctuate slightly (especially if using MAP based AE). The number you should enter in the ‘deadband’ box should be slightly higher than this number, such that AE is not triggered by normal steady state (no throttle movement) driving or idle conditions.

At higher engine speeds (RPM), AE is not really needed, and you can set at which point we start to ignore AE in terms of RPM with the Acc. Enrich RPM Clamp Trim table. In the above screen shot you can see at 2500 RPM we only apply 12% (0.12) of the calculated AE enrichment value, and above 4000rpm we don’t apply any extra fuel at all. This will of course depends on your engine, and would be part of the tuning process.

The most crucial part of the AE tuning is the Hold Rotations, Decay Rotations and the main PW Table Acc. Delta Enrich.

When we enter the AE algorithm (i.e when we detect a Delta of larger than the deadband) we take an initial VE reading of the engine from the main fuel map (lets say 40 in this example). We then multiply this number by the number calculated in the PW Table Acc Enrich. So in the above table we can see that as we have more delta (or quicker change in the throttle) we have a larger number, but lets say for example this table yields ‘1.5’ at the current delta, so the result would be 60. We then add 60 to our original VE, and we are given a total calculated VE of 100.

There are a couple of other tables taken into account such as a Coolant based modifier (AE CLT Trim(. For those wanting a full algorithmic description, the formula looks like:

The multiplier is calculated first as the reading in the AE Table * RPM multiplier (different AE based on RPM) * CLT Multiplier (different AE based on CLT)

Then that value is multiplied with the VE reading and the result gets added to the original VE calculation. So, example:

VE - 70

Resultant trim = AE trim * CLT Trim * RPM trim (0.5 * 1 * 1 )

VE Added = 70 * 0.5 = 35

Total VE used for fuelling = 70 + 35

Now we apply this enrichment consistently to the VE from the main map for the amount of ‘hold rotations’ of the engine (engine cycles) which may be 3 or 4 or 5 etc, and once the engine has performed this many rotations we then decay the fuel off evenly over the ‘Decay Rotations’.

The end result is a burst of extra fuel with its size being related to how much we have opened the throttle, which then tapers down, all the while taking into account the clamp modifier amount based on RPM, and by the time the AE extra fuel has decayed off, the normal VE table should be applying the correct fuel to keep the engine at the desired AFR.

Variables used in AE Algorithm

AE Delta

This is the current delta (rate of change) of the AE signal. This will either be TPS or MAP based on the AE Settings. 

Inj. AE VE Added

Because the ECU is VE based, instead of adding a pulse-width directly to the injection time, instead an amount of "VE" is added (such as 32%), simulating extra air being drawn into the engine which the VE equation then computes the extra fuel requirement for. As an expression, AE VE Added = AE VE Trim x Current VE.

AE VE Trim

The multiplicative AE Trim value looked up from the Inj. AE Trim table.

AE Captured Delta

When the delta rate goes above the threshold set in the AE Settings, the Delta is captured, which is then looked up in the Inj AE Trim Table to work out the VE multiplier (AE VE Trim) to add to the base VE.

AE CLT Trim

An overall trim to the AE VE amount based on coolant temperature - this compensates for cold engines needing more AE fuel.

AE MAP Delta

The current rate-of-change of the Manifold Pressure

AE TPS Delta

The current rate-of-change of the Throttle Position. (Note this comes from the "AE TPS Equivalent Load Table", which is typically mapped 1:1.

AE TPS Equiv. Load In

The current input into the Equiv Load table from the TPS or DBW module.

AE TPS Equiv. Load Out

The resultant TPS value used to calculate delta when using TPS as an input source. Typicall this table is mapped 1:1 from 0 to 100%.

AE when using Drive-by-Wire

Note that when using drive-by-wire throttle setups, the Pedal Position will instead be read from the Equiv. Load table. (To smooth out any idle control modulations before they trigger AE.)