Throttle cracker. Does it use corrected airflow values, or base table values?

[Jim_PA]

If rolling at low speed and low RPM, lets say 15MPH and 1200 RPM... and I push in the clutch, RPM hunts up and down and sometimes tries to die.

As soon as throttle cracker is disabled (under 4mph) my idle immediately stablizes.

STIT and LTIT are now into the negative numbers, so I don't think adding more base airflow is the right thing to do.

I've been through the tutorials and made timing adjustments to both base and high/low octane, as well as changing the other things as suggested in tips and tricks.

If throttle cracker enabled = base airflow + throttle cracker airflow, and base seems to be pretty close, why the huge change in idle quality between rolling at 10mph and sitting stationary?

What steps would you take in trying to figure this out?

I don't have a clutch switch... is this causing me big problems that I won't be able to correct?

I'm using COS3 by the way!

Thanks

[Jim_PA]

It would appear that the clutch switch signal at the PCM is open when the clutch is pushed in, and closed when the clutch is left out...

And since I don't even have a wire going to the CPP pin on the PCM, it's obviously in the open state all the time.

So, my PCM is always operating in P/N throttle cracker table??

That might explain why adjusting the throttle cracker in-gear table doesn't seem to be doing a whole lot.

However, it still doesn't explain why it wants to dip around and stall at low speeds, since at a dead rest, the idle is great.

I'm starting to think that throttle cracker uses explicit values from the idle airflow table, rather than a corrected value, but that doesn't seem logical, does it?

[5.7ute]

Log the various airflow tables to see what parameter is causing your unstable idle issues.
I have noticed in some of my logs some strange behaviour with throttle cracker values. For instance I had TC airflow being added with a zeroed out table,though this may be an issue with the COS I use (01290005), or an undefined parameter being active.
For the record a manual car is always seen as in gear by the pcm.
Also note that too high an airflow value can cause the issues you are having.(that & too rich an idle mixture caused me to have similar issues)

[macca_779]

I don't even use cracker anymore. Desired air is set to cause the rpm to drop to ~800 with the clutch in while moving. I really don't see a need for it.

[Jim_PA]

That's not a bad idea. Might have to try it. Can't say I really enjoy TC all that much anyway.

I might try to sort it out first, and try it both ways. I'll try to do some better logging.

[macca_779]

That's not a bad idea. Might have to try it. Can't say I really enjoy TC all that much anyway.

I might try to sort it out first, and try it both ways. I'll try to do some better logging.

You just have to ignore a few basic principles that we've always gone by for desired air tuning. The RAFIG process is severely flawed once you start playing with aftermarket cams. Just give the engine what it wants and don't be to stressed about the data. Took me a long time to learn and accept that.

I do desired air tuning all by feel now. The MAF technique I'm sure works ok too. But the way I see it if I have no modifiers being applied (follower/cracker) and the revs dip below 800 there isn't enough desired. If it hangs, there is to much. But keep in mind you must be in a non idle condition to do this, ie moving to prevent idle correction techniques doing their thing.

You'll never have to over drill another throttle again in my experience massaging desired air.


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[Jim_PA]

You just have to ignore a few basic principles that we've always gone by for desired air tuning. The RAFIG process is severely flawed once you start playing with aftermarket cams. Just give the engine what it wants and don't be to stressed about the data. Took me a long time to learn and accept that.


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The last time I had throttle cracker disabled, I noticed that if I left off the gas while it was in gear and coasted that way for more than a few seconds, then pushed in the clutch, it would try to stall. I learned how to drive my car differently... If I coasted in gear for more than a split second and then pushed the clutch in, I'd bump the gas pedal so it would re-start the idle-down process (or whatever it was doing)

I think what was happening is that when off the throttle and in gear, it was trying to correct the idle speed by taking out all the air, then when actually pushing in the clutch, it was so restricted it would fall right down to a stall.

Have you ever run into this when not using the TC?

[macca_779]

The last time I had throttle cracker disabled, I noticed that if I left off the gas while it was in gear and coasted that way for more than a few seconds, then pushed in the clutch, it would try to stall. I learned how to drive my car differently... If I coasted in gear for more than a split second and then pushed the clutch in, I'd bump the gas pedal so it would re-start the idle-down process (or whatever it was doing)

I think what was happening is that when off the throttle and in gear, it was trying to correct the idle speed by taking out all the air, then when actually pushing in the clutch, it was so restricted it would fall right down to a stall.

Have you ever run into this when not using the TC?

Absolutley I've see it, I've pulled my hair out trying to understand why this happens when desired is already tuned off idle trims.
But remember idle correction will not apply until in idle mode which is normally below 1 or 2 km/h. With yours zero the cracker and add 1.5g to desired. Bet you it fixes it.


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[Jim_PA]

But remember idle correction will not apply until in idle mode which is normally below 1 or 2 km/h.
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Then it still doesn't make any sense at all, since simply tapping the gas pedal while moving is all it takes to make it not happen, but I will take your advice and keep trying :D

[macca_779]

Here is something to think about. Mate of mine has a VL Walkinshaw with an aftermarket cam on an OEM tune. The way he gets this thing to idle and behave properly wihtout stalling all the time is to let it idle and he disconnects the iac to hold it where it is. This car rarely misbehaves. Starts rather ordinary without pedal, but that is to be expected with this approach.

Him effectively freezing the iac is what led me to my approach with idle tuning. At least with us we can effectively do this electronically. Sure I still retain some follower in my tune. But it decays very quickly and frankly does bugger all. So besides the start up areas which add air accordingly my iac does bugger all once up to temp


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[macca_779]

Then it still doesn't make any sense at all, since simply tapping the gas pedal while moving is all it takes to make it not happen, but I will take your advice and keep trying :D

Id say it was your follower air being applied when you tapped the gas that was saving it. Log your follower and cracker air and you'll see why it was helping. Iac steps is a good real data way to view iac behavior too.


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[Jim_PA]

So, desired airflow table is essentially the IAC of the DBW system? Just checking my sanity here ;)

[Jim_PA]

Id say it was your follower air being applied when you tapped the gas that was saving it. Log your follower and cracker air and you'll see why it was helping. Iac steps is a good real data way to view iac behavior too.
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Ahhhh... that makes sense. Tunnel vision tends to kick in with me sometimes...

[macca_779]

I think what was happening is that when off the throttle and in gear, it was trying to correct the idle speed by taking out all the air, then when actually pushing in the clutch, it was so restricted it would fall right down to a stall.


This is why it's important not to allow idle mode when in a condition other than pretty much stationary. It will like you said pull all air up to the allowed trim limit to try and correct the overspeed but naturally it's impossible when still coupled to the drivetrain.


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[macca_779]

So, desired airflow table is essentially the IAC of the DBW system? Just checking my sanity here ;)

It's base airflow. How it's actuated be it ETC or IAC it's still the same.

Therefore since its the base air, or minimum air. The IAC will never go below it which will always be enough air to sustain min idle. There are of course situations where it can dip.. But that's where timing comes in to do the fine work correction.


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[Jim_PA]

This is why it's important not to allow idle mode when in a condition other than pretty much stationary. It will like you said pull all air up to the allowed trim limit to try and correct the overspeed but naturally it's impossible when still coupled to the drivetrain.


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Yeah, I'm pretty sure I set idle mode as per the tutorial... any speed below 256 at throttle > 1.19%

Thanks for helping me piece this together! -- I'll give it a few more tries and hopefully report back with my huge success story :)

[macca_779]

Yeah, I'm pretty sure I set idle mode as per the tutorial... any speed below 256 at throttle > 1.19%

Thanks for helping me piece this together! -- I'll give it a few more tries and hopefully report back with my huge success story :)

I've never read that tutorial. But if you think about it I'm sure you can see why its a bad idea to have idle mode allowed to be enabled off near stationary speed.


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[Jim_PA]

So I disabled TC, and set non-idle mode to > 1mph and > 1.2% TP (the way I read it, both conditions must be met, and if not, it's considered idle mode).

I increased airflow by 1.5, and then by another full 1.0 after an unsuccessful test drive.

RPM falls like a stone if clutch is pushed in while coasting in gear (the drop is worse at higher RPM)

while coasting in gear, TP% goes down to 1.2% - TP% doesn't try to recover until it drops below 700 (I'm guessing stall saver kicks in). Idle TP% while sitting still is around 4%

I can't seem to figure out how to increase the minimum TP% so it doesn't fall all the way down to 1.2% during a coast in gear.

I'm going to venture into the ETC tables, especially B2717 "Minimum Throttle Blade Position" unless anyone has any other ideas.

Attached is latest tune file

12550

[DrkPhx]

So I disabled TC, and set non-idle mode to > 1mph and > 1.2% TP (the way I read it, both conditions must be met, and if not, it's considered idle mode).

- I would leave those values stock, and use the Throttle Follower tables to fix the problem. The rapid rpm drop from clutch engagement is amplified when the Cracker tables are disabled. You need to add airflow to the lower cells in the Follower Airflow table to add a cushion AND decrease the values in the Decay table. How much depends on your specific vehicle. Depending on the vehicle it can be a tedious task to get it right using those tables. The scan tool is your best friend in this case; guessing will just cause more frustration.

I increased airflow by 1.5, and then by another full 1.0 after an unsuccessful test drive.

- To what tables?
RPM falls like a stone if clutch is pushed in while coasting in gear (the drop is worse at higher RPM)

- See above. Using the scan tool, you need to pinpoint the exact mph it's happens at and work from there using the Follower tables. Once again, it's trial and error. Don't be afraid to make large adjustments to see what the vehicle likes. For example if you fix the problem but now have a hanging idle or cruise control effect, methodically change the values to find a happy medium. Once again, each vehicle responds differently.

while coasting in gear, TP% goes down to 1.2% - TP% doesn't try to recover until it drops below 700 (I'm guessing stall saver kicks in). Idle TP% while sitting still is around 4%

- Does this happen with the stock idle parameter values?

I can't seem to figure out how to increase the minimum TP% so it doesn't fall all the way down to 1.2% during a coast in gear.

I'm going to venture into the ETC tables, especially B2717 "Minimum Throttle Blade Position" unless anyone has any other ideas.

[macca_779]

I can't really help with ect stuff as all my experience with large cammed engines is cable based

[Jim_PA]

So I disabled TC, and set non-idle mode to > 1mph and > 1.2% TP (the way I read it, both conditions must be met, and if not, it's considered idle mode).

- I would leave those values stock, and use the Throttle Follower tables to fix the problem. The rapid rpm drop from clutch engagement is amplified when the Cracker tables are disabled. You need to add airflow to the lower cells in the Follower Airflow table to add a cushion AND decrease the values in the Decay table. How much depends on your specific vehicle. Depending on the vehicle it can be a tedious task to get it right using those tables. The scan tool is your best friend in this case; guessing will just cause more frustration.

I increased airflow by 1.5, and then by another full 1.0 after an unsuccessful test drive.

- To what tables?

I was referring to desired airflow B4307

RPM falls like a stone if clutch is pushed in while coasting in gear (the drop is worse at higher RPM)

- See above. Using the scan tool, you need to pinpoint the exact mph it's happens at and work from there using the Follower tables. Once again, it's trial and error. Don't be afraid to make large adjustments to see what the vehicle likes. For example if you fix the problem but now have a hanging idle or cruise control effect, methodically change the values to find a happy medium. Once again, each vehicle responds differently.

while coasting in gear, TP% goes down to 1.2% - TP% doesn't try to recover until it drops below 700 (I'm guessing stall saver kicks in). Idle TP% while sitting still is around 4%

- Does this happen with the stock idle parameter values?

Yes, it doesn't seem to matter what I do. If coasting in gear for more than a second or so, the throttle seems to slam shut.


I can't seem to figure out how to increase the minimum TP% so it doesn't fall all the way down to 1.2% during a coast in gear.

I'm going to venture into the ETC tables, especially B2717 "Minimum Throttle Blade Position" unless anyone has any other ideas.