Tuning for Fuel Accel Enrichment

[mr2andy]

Hey guys,
I finally got my car tuned at the dyno and all the fuel map and ignition map are done. The tuner tuned for the fuel enrichment as well but I thought it can be done better.

I plan to log the data and do some street tuning myself on the accel fuel enrichment setting and would like to have some tips before I starts.

Beside any suggestions from any of you, here are some of my questions. Base on the current setting and logging data, I get a spike up(lean) in A/F(lambda) the moment I accelerate, then the curve comes down showing rich.

1) Assume a properly tuned accel enrichment should give a flat curve on A/F(lambda)? meaning regardless the rate of acceleration, the lambda should not have drastic spike up and down?
2) Base on the logging data above, is that mean I should up the accel fuel sensitivity at the same time up the accel fuel decay? The more sensitive setting should take care of the lean part of the accel and the high accel fuel decay should take care of the rich part of the lambda?

My understanding on accel enrichment as below..
Accel Fuel Clamp : The maximum % fuel enrichment for acceleration
Accel Fuel Decay : How quickly the computer will remove this enrichment
Accel Fuel Sensitivity : How frequent should the computer recalculate the fuel enrichment due to whatever the x-axis(rpm, TP%)

Please correct me if I'm wrong.

Cheers
Andy

[stevieturbo]

Proper accel enrichment gives good throttle response using the least amount of fuel possible.

AFR's are totally and utterly irrelevent ( other than to perhaps diagnose a problem based on you feeling a problem also ), so dont try and target them. If you cannot feel a problem when you change the throttle opening. Then there isnt a problem.

Sensitivity is how likely it is to add enrichment based on how you moved the throttle

[MarkMc]

You have the basics right but like Stevieturbo says I would usually tune it until there is no obvious signs of a hesitation rather than trying to get a perfectly smooth LA curve.

If it goes lean after the fact this could be due to not enough decay.

Getting rid of the LA lean spike altogether may be a little impossibe.

I owuld leave the Clamp where it is and go up in sensitivity and watch the logging and the feeling of the car. If you get to about 80-90% sensitivity and you still have a way to go then make the Clamp slightly bigger. Do the decay last.

[mr2andy]

Thanks for the information guys. Before I made any changes to the current accel setup, when I do any normal acceleration, I can see the lambda jump to around 1.8 and the car seems to hesitate a bit. As I up the accel sensitivity setting, the lambda now jump to around 1.4 and the acceleration feels much much better.

One thing I'd like to understand is.. on a typical Accel Fuel Clamp setting as below...

RPM-----0-----1000-----2000-----3000-----4000-----6000-----8000-----10000
-------- 40-------30---------20-------10---------0----------0---------0---------0

What does this actually mean? Does it mean when I'm accelerate from 1000rpm to 1500rpm, the extra % of fuel will be some value linear to between 30-20?

From the table above, the reason the extra % fuel decrease as the RPM increase is because as the rev pick up, the computer do more calculation anyway therefore the accel fuel isn't necessary?

[mr2andy]

Anyone? I'm trying to understand how the ECU calculate Accel Fuel...

Thanks in advance..

[MarkMc]

The clamp is the value used by the calculation at the time Acceleration Enrichment in requested. It is the RPM at that instant that is used to look up what the clamp should be. The Sensitivety is what decides how much of the clamp is used.

As the engine gets higher in the RPM range you can understand that the throttle will be open more, so giving it more throttle instantly (e.g. 60-100%) will not give as high a change in effieciency...therfore less need for accel fuel. It can depend on the size of the throttle body and engine.

What you want to do is start at, say, 2000rpm and jump on the throttle, tune the Accel fuel until it works well. Next go to 3000rpm and do the same. Next 4000rpm and so on. Depending on the engine you may get to 5000rpm and find that there is no Accel fuel needed at all. Try it in different gears as well.

[mr2andy]

Thank you Mark.. I'll give it a shot