Explain throttle cracker and follower..again!

[SSpdDmon]

The bitch about idle is, it seems like every car is different. For example, my '01 H/C M6 SS idles fairly well with the stock tables and only needed a few adjustments. On the other hand, my friend's cam-only '00 A4 WS6 needed a little more tweaking.

Usually, spark is a major contributor to idle issues. So, keep that in mind while working on idle. Bi-directional controls will be a lifesaver for spark. What I usually do first (after some initial spark adjustments) is set the desired airflow table using the RAFIG and RAFPN (for autos) by logging from several cold starts. One trend I notice here is the curve tends to smooth out a bit (kinda looks more like a hockey stick). Once that is done, you have your base. Throttle cracker will be added to this base and the throttle follower will be either added or subtracted from this depending on changes in RPM. **On a side note, I usually adjust B4308 based on the changes I made to the desired airflow. Just be aware of the different coolant temp scales between the 2 tables.**

The next thing I do is take about 50% out of the cracker & follower airflow tables (B4309 & B4315). My theory in doing this is, there's more of a cam now so less compensation is needed. The same theory can be applied to the 3 airflow tables (B4512, B4514, & B4515) that control the IAC. Their overcompensation can be the cause of some surging too (mainly on A4's). Tweaking the throttle cracker further is best done by logging the idle pid for it. Then you can see when it's being applied and whether or not it's jumping between cells (up...down...up...down) causing surging.

IAC effective area should be left alone assuming airflow to the IAC valve is still unobstructed. Epoxied TB's can be the cause for some problems with idle airflow. In that case, you can try tweaking this table. But, chances are it's just easier to get rid of the epoxy.

The tricky part is doing all of this while keeping an eye on spark. Jumping between the high/low tables and the base tables can be the source of surging as well. Usually, cam'd cars like 42~45 degrees of timing during decel under 2400 RPM. The trick is to figure out where your grams/cyl are at for 0% throttle decel and set the cells around there to a single number (ie all cells .08~.24 and 1200~2400RPM to 43 degrees). Generally, you want to do this until just before idle (or when the TCC is going to unlock) in the high/low and BSIG tables.

Playing with those tables is the best way I've found to tackle the real issue...surging. To answer your original question though...the TC is always added to the desired airflow (when enabled) for the given MPH/RPM cell. Too little can choke the motor down and too much can cause a cruise control effect. The TF is subtracted from the base (desired airflow) during increasing changes in RPM and added during decreasing changes in RPM. This essentially softens the blow of changes made by your right foot for both more or less throttle.

Well...that's my $0.02 on the matter. Hopefully it helps someone.

[Aint Skeered]

I am trying to get my Nova to Idle. I am not using o2 sensors, running open loop all the time. Can you still do the Rafig without 02's?

also is this what you were talking about sspdemon on spark?
I only changed it in high octane timing untill some one confirms this is what it should look like. it looks excessive to me.

[SSpdDmon]

Wow - thread from the dead! LOL

If I get a chance later, I'll take a look.

[Aint Skeered]

It just shows I am searching

[The Alchemist]

One last thing is what table controls air on cranking/startup? Airflow Parked?


The other guys have answered the TC TF stuff spot on. All I have to add here is that I tend to set the TF by travelling at 100km/hr then throttling off and logging the decell right down to 5km/hr or so. The car should decel at a constant rate, depending on your personal preference really. If certain speed zones exhibit a cruze effect or too much decal make the alteration on the TC table in the logged zones. Most of the TC table is never actually "used" ....
Also another critical spot is say at 100km/hr and you approach a small to medium downhill stretch you throttle off, you want the car to mantain speed downhill and not race away or slow down excessively making you break the DCFO benefits to maintain speed by touching the throttle.....

With airflow parked I have found this useful in fixing the warm start/instant stall with a cammed engine. Simply bumping up these numbers slightly say 1g/s at 60 to 80deg centigrade opens the IAC a bit more at startup and makes starting more consistent.
Cheers,
Mike

[SSpdDmon]

One last thing is what table controls air on cranking/startup? Airflow Parked?


The other guys have answered the TC TF stuff spot on. All I have to add here is that I tend to set the TF by travelling at 100km/hr then throttling off and logging the decell right down to 5km/hr or so. The car should decel at a constant rate, depending on your personal preference really. If certain speed zones exhibit a cruze effect or too much decal make the alteration on the TC table in the logged zones. Most of the TC table is never actually "used" ....
Also another critical spot is say at 100km/hr and you approach a small to medium downhill stretch you throttle off, you want the car to mantain speed downhill and not race away or slow down excessively making you break the DCFO benefits to maintain speed by touching the throttle.....

With airflow parked I have found this useful in fixing the warm start/instant stall with a cammed engine. Simply bumping up these numbers slightly say 1g/s at 60 to 80deg centigrade opens the IAC a bit more at startup and makes starting more consistent.
Cheers,
Mike

I prefer the startup friction airflow correction table. B4343 IIRC.

The reason why is you can adjust the decay rates based on ECT where as the other table you mentioned has one decay rate. Also, B4343 doesn't decay as fast.

[NASABlue]

Good info!!!