"Accelerator pump" action

[PSWired]

Can someone explain how the LS1 PCMs provide instant enrichment during throttle transients? I see no tables that relate enrichment to throttle transients, can someone explain it to me?

[ringram]

My thought on this is as follows.
In a carb you need a shot because the velocity of air doesnt change fast enough to pull more fuel in. However in an efi engine you will be sitting at one point in the VE table next second you are at a much higher point so the system instantly throws the extra fuel in as required by the table, no need for the extra shot as the correct fuel is dumped in immediately (+ any PE enrichment due to TP settings) Of course I may be wrong, but after not seeing anything similar thought that this might explain it...
Would be interested to hear one way or the other..

[caver]

That is true but additional fuel still needs to be injected to cover the transition between those points.
Remember the processor must react to events and no matter how fast it is there is always a delay before it catches up.

If you map a stand alone system you will be amazed at the amount of accell enrichment is required especially on the 8's.

[ringram]

Which then begs the question... where is this in efilive? Or is this table not available for messing with?

[caver]

I imagine so

[PSWired]

I remember such a table being present in my days of tuning the TBI engine in my 95 Yukon- TunerCat had a table in it called "Pump Shot." Differential TPS was the independant variable (in %) and the added injector pulse width in microseconds was the dependant variable. It went from 0-25% if I remember correctly. Any such thing in EFILive?

[caver]

Not that I have seen

[PSWired]

Hopefully one of the developers will chime in here.

[deezel]

Look at the throttle follower tables. These are set up to add extra airflow when the throttle position changes rapidly - like an accelerator pump. The extra "airflow" added to the PCM calculated value results in more fuel being injected.

[ringram]

Very cool. Just when I thought I was happy with my tune.. Now I have more things to play with.. Ill have to see if I can "kick start" throttle transitions.

[deezel]

I haven't really played with the throttle follower tables - just had some of them messed up in a corrupted flash one time. Please update if you do experiment with them.

[ringram]

Ok, I played with this today.
Basically changed 1200 rpm multiplier to 3 from 2.5 and set the next one up to 2.5. I also scaled the lead in linearly so that 3.75% TPS is 0.75 etc this had the effect of making the throttle much more responsive.

By the looks stock it doesnt do much till around 13% TPS when it is inreased 6 fold! So ramping it up makes the throttle much more responsive on transition from idle. I havnt gone too much more on this as I had some sideways action in 2nd and 3rd gear at low throttle in the wet so suspect its about right :)
You could make it too touchy if you arnt careful, as it is its still linear and progressive, just more aggressive.. I like it!

So in summary, yes it appears it does in fact have a "pump shot" like effect.

Tables I changed were B4315 and B4316 at the 3% TPS and 1200 RPM cells.