Accel/Deccel Comps

What is a good way to dial in the accel/deccel comps?

Thanks

I always start by making sure my main fuel map is correctly tuned. If it isn't you may end up trying to tune around a problem in the main fuel map using accel enrichment and this is never going to work well.

Tuning the accel enrichment is done as much on feel as it is by watching the wideband meter. Since we are looking for such an instantaneous result, it's the feel or response of the car that's most important. You will find a small amount of lag in the wideband displaying the accel event. The accel enrichment settings will also vary widely from ECU to ECU. In general you will have settings defining the sensitivity, or how much throttle input is required to request accel enrichment. You will also have an enrichment table and often a decay table which defines how quickly the additional fuel enrichment is removed.

Starting with the sensitivity, you want to make sure that the accel enrichment is only active when you really want it. You can log the accel enrichment and this will show you when it is being added by the ECU. It's quite common to see some noise on the TPS input and if the sensitivity is too high, this can result in accel enrichment when you are driving at a constant throttle setting. This can cause some very frustrating problems with your AFR that can be hard to track. Conversely when you make a sharp throttle position change you want the ECU to deliver accel enrichment.

Once the sensitivity is adjusted you need to tune the enrichment and decay tables. Generally these will be either 2D relative to engine rpm or 3D relative to rpm and load. You will find that due to the higher airspeed, accel enrichment can be greatly reduced at high rpm/high load. The most critical area is from a closed throttle (or almost closed throttle) at idle and low rpm. You can adjust the enrichment tables until you get good clean throttle response on a sharp throttle input and your AFR is relatively flat. If the AFR is initially good during a throttle transient but then tapers either rich or lean, you can use the decay time to correct this.

Lastly you may also have the ability to adjust the accel enrichment relative to ECT. Usually you will find that the engine needs extra accel enrichment when cold.

We will run a webinar on accel enrichment at some point to help illustrate these settings better.

Would love to see a webinar on this!

Point taken! It's a great idea. We will look into it.