Stalling in Dashpot Mode

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Stalling in Dashpot Mode

Unread postby wickedsnake00 » Tue Oct 02, 2018 7:29 am

Background: CVAF1 strategy, 03 Cobra engine, HPX-E MAF, FR500 cams, ported Eaton w/twin 66s. Stock TB and IAC. Tuned with SCT Advantage III.

I have an issue with it settling to idle, sometimes stalling out. I ran a hot throttle snap test, sitting stationary. I let it sit for awhile at idle, integrator at 0, then blipped the throttle. Idle speed control mode goes to -1, indicating dashpot. Desired air mass at idle and idle air valve duty cycle jump up and start to decay with dashpot. RPM drops, but around 74.5s (~7 seconds after the throttle snap), it hits the desired idle rpm, even though desired air mass is above what it should be at stable hot idle (0.94 vs 0.82 at idle). Idle air continues to drop, and so does RPM rather quickly down to 200, almost to the point of stalling, briefly recovers, and then stalls. All this time it's still in dashpot, not base idle.

It looks like the dashpot function is essentially an open loop system where it decays from the pre-position down to the isc neutral idle air value at the dashpot decay rate, no RPM feedback or anything. That said, is it undershooting due to the decay rate, or is it something else that needs to be adjusted? I know that regardless it needs to be leaned out a lot more at idle- I adjusted injector timing, and need to compensate for it a lot more. It's hanging in the 13s to high 12s. And the MAF signal is noisy, but there's not anything I can do about that.

For dashpot decay rate (FN879) values I'm using close to your values-
16 - 0.04
0.75 - 0.02
0.5 - 0.01
0.25 - 0.005
0 - 0.0015

I also assume that the left column in that table represents the delta from base idle airflow. Is that correct?
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Re: Stalling in Dashpot Mode

Unread postby decipha » Tue Oct 02, 2018 8:08 am

not surprising at all the 4v engines are very dashpot needy engines. You need to kick up the minimum dashpot value to allow idle feedback. I think they call it the dashpot for zeroing the entry timer or something along those lines should be easy to find. Set it to 0.500 should fix her on up.

Be sure to set the minimum mph for idle control to 25mph and the dashpot min mph to 0.5mph and hysteresis to 12 mph. That's very important. And it would be wise to reduce the dashpot decay significantly below 0.250 dashpot. I usually set it to a decay rate of 0.0007

the left values are the dashpot value the right is the decay rate
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Re: Stalling in Dashpot Mode

Unread postby wickedsnake00 » Sat Oct 06, 2018 7:41 pm

Awesome help.

Now is that to say that the "dashpot for zeroing entry timer" represents the amount of dashpot where it transitions from dashpot control to idle control? I haven't been able to find a parameter description for it anywhere. The default value was 0.02, which seems pretty crazy if that's the case.

I made most of the changes, but didn't find any related to hysteresis in dashpot or idle.

As for results it seems to have eliminated the issue when warmed up at least; no more than a 50-100 RPM undershoot. I've still got some tweaking to do, and logging it will help me determine just what needs to be changed.
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Vehicle Information: 00 Mustang GT, 4.6 DOHC, Eaton M112, twin 66mm, FTL1, SCT PRP tuning, 60lb/hr injectors, HPX-E MAF, FR500 cams, dual GT fuel pumps, 9.1:1 CR, T56 manual transmission

Re: Stalling in Dashpot Mode

Unread postby decipha » Sun Oct 07, 2018 12:03 am

yes that's what it does

no surprise sct is prob missing the hysteresis parameter

sounds like you need more dashpot, go kick up the pre position / max dashpot function and slow down the decay
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decipha
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Re: Stalling in Dashpot Mode

Unread postby mvancopp » Thu Oct 11, 2018 1:22 pm

I was having a similar issue and the prior posts solved the dipping idle, and stalling, when shifting or coming directly out of gear to coast. However if you take your foot off the gas and let the engine drag for more than a few seconds and then press in the clutch the same deep RPM dive occurs and sometimes stalls. The RPM dip is greatest if you are in a low gear (1st or 2nd) and release the gas pedal and allow the RPMs to drop to around 1800 RPMs, taking 2 - 3 seconds, and then press in the clutch.
Do you have any pointers on what to look for under these conditions?

Thanks for any help you can provide.

FYI: I also am using SCT Advantage and could not find the hysteresis setting.
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Re: Stalling in Dashpot Mode

Unread postby decipha » Thu Oct 11, 2018 7:41 pm

set minmph to 25 mph should fix that all up

minmph is the minimum speed to allow idle spark control
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93 auto - Danika
94 5spd Rionda
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Re: Stalling in Dashpot Mode

Unread postby mvancopp » Sat Oct 13, 2018 9:00 am

Thanks for the reply.

The idle minmph is already et to 25. I followed your suggestions in the second post, your first reply, of this thread.
Do you have any other suggestions or suggestion for logging that may help point in the right direction.

Thank you,
Mark
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Re: Stalling in Dashpot Mode

Unread postby decipha » Sun Oct 14, 2018 8:19 am

make sure idlrpm is high enough 650 or so that it goes in to idle spark feedback well before its at a low rpm so spark doesnt drop and the bottom falls out
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decipha
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Joined: Mon Jul 15, 2013 5:29 pm
Location: New Orleans, LA
Name: Michael Ponthieux
Vehicle Information: Supercoupin' x10
90 (4x 5spds) - Dante, Ruby, Daja, Ava
91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce


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