[d347643]

I attached a short datalog right after restarting the car when warm/hot. I am noticing three things here. The hego's are reading .8 which is indicative of a lean burn. The lambses are rich and then as they lean out the idle obviously stabilizes. The iac isn't even trying to compensate. Is this a correct interpretation? Take a look at the timing too, it's going crazy. Is this just a classic "too rich" restart issue or could something like this be caused from the timing. I know I could unplug the spout and see if it helps but I couldn't get out of the car fast enough haha

thanks,

Drew

[Chucko]

HEGOs above .4V is rich, not lean.

I may have more to say after I grab the log file.

[Chucko]

OK, first off, you need to sample at a much higher rate. Twice a second isn't nearly enough to figure out a dynamic problem like this. I usually sample at 50ms.

Second, in my (limited) experience, a surge like this starts due to the ISC overcorrecting the initial overspeed after exiting crank mode. ISC duty cycle is a big hammer and RPM responds relatively slowly to ISC changes, resulting in an oscillating idle if ISC corrections are too active.

The usual cycle is: the engine catches and revs above target idle. ISC closes too far too quickly, now the engine is almost stalling. ISC opens up too much too quickly to compensate and and the RPM overshoots. Now ISC closes down too far again, and the engine almost stalls again. Rinse and repeat.

Try dropping FN824 values above your target (hot) idle speed. A9L has something like 3.0 for values above target idle, my tune has 1.5 in that part of the curve.

I also made the initial slope of FN810 much shallower than stock. This function controls how ISC responds to severe underspeed. The factory curve kicked my combo into oscillation if I didn't come out of gear fast enough at a stop sign.

Both FN810 and FN824 are in terms of absolute RPM and should be adjusted for your combo's target hot idle speed if it isn't the factory 672 RPM.

Also try reducing KPSIND and KPSINU, the ISC gains for over- and under-speed in neutral respectively.

There is a LOT more to idle tuning, especially at startup, but this should help you get the ISC overcorrection under some control.

Spark is bouncing all over in your log because the GUFB strat uses spark as the first line of idle speed control, for good reason: the engine responds much faster to changes in spark timing. Spark isn't causing your problem, it's trying to correct the surge.

Last, your LAMBSEs are a tad rich for hot start, but they're not causing any problems. You can ignore this unless you're a fanatic about fuel efficiency.

Give the corrections above a shot, dial down the logging interval, and let us know what happens.

[d347643]

Try dropping FN824 values above your target (hot) idle speed. A9L has something like 3.0 for values above target idle, my tune has 1.5 in that part of the curve.

so you're saying the 3x multiplier above the valley is aggravating it? My target idle speed is 888 and my actual is around 850 as you can see from the log. I'll make changes and report back tomorrow. Just thinking out loud but wouldn't clipping the min flow of the isc also help how the isc reacts to the overshoot?

thanks for the help man,

Drew

[Chucko]

I was only looking at the first 10 seconds of your log. Now that I look at the whole thing, there's some other funny stuff going on.

Around 139 seconds, the LAMBSEs start to rise (as expected), and immediately idle RPM takes a dive. Spark and ISC duty cycle increase to compensate for the drop in RPM, but it looks like spark is pegged at the max. I don't understand why ISC duty isn't higher here, it's flat at about 53%. It looks as if the ISC functions aren't in sync with the idle spark functions.

Can you post your tune with your next log?

[d347643]

sure thing. Maybe my base is too far advanced?

[Chucko]

Make sure your logging payload includes IPSIBR. This is an internal measure of how much air the ISC needs to add or subtract to reach the target idle.

[d347643]

haha I just realized the title of the thread is retarded, I can't believe I wrote that. helped my? haha oh well.

Ok, attached is my tune and datalog as I was leaving the gym with a warm restart. Interesting how there was no surging...what gives? Something that did happen was the car almost stalled when coming to a stop in neutral. The rpm seemed overshot my idle on the decel and then surged a few times before mellowing out. It seems that two scenarios happen when I'm coming to a stop:

1. The rpm will hover a little over 1200 and then drop like a rock to about 850 right before I come to a complete stop.

2. The rpm drops to my idle speed and flares back up to about 1200 before coming to a stop and then dropping like a rock to 850. The problem with this scenario is that if I throw it in neutral with the rpms pretty high, the rpms will drop so fast that when it hits my idle speed it surges trying to maintain the idle.

thanks,

Drew

[Chucko]

OK, finally got time to look at your log and tune. I'll do a more detailed analysis if I can find time this weekend.

In the meantime I've attached a revision of your tune with a couple of changes, mostly in the dashpot PIDs and functions.

DASMIN and DASPTO have been bumped up to correct the almost-stall when coming to a stop. Stock is .0938 and .05 respectively, I set them both to around .14 in my tune.

I copied FN879, the dashpot decay rate, from my tune. This curve is a lot more gradual than stock. This should help with the RPM dropping like a rock.

I adjusted FN824 to center the "dip" around your desired idle RPM. This wasn't causing any problems, but it will make the ISC duty cycle less sensitive to minor idle speed changes around the target RPM.

I didn't change your higher-than-stock value for DEBCYP, but I don't see why you should need this, if the above dashpot stuff gets us in the ballpark.

Can you add DSDRPM to your logging payload? That way we can see what the EEC thinks the idle RPM should be.

Give it a spin and let's see what needs adjusting next.

[decipha]

you missed fn810

[Chucko]

If FN824 does its job, he's less likely to need FN810. The old FN824 wasn't offering enough help for mild underspeed conditions.

"Modifying FN810 is left as an exercise for the student."

[decipha]

oh word? no doubt!

[d347643]

awesome, very much appreciated. Ok as far as fn810, is this just an isc adder to prevent stalling? when the rpm drops low it will open up the isc to bring it back up? I clipped the min duty cycle of the isc (debyc) via a post of Decipha's.

goin to my mom's for dinner, let you guys know how it all works out with the datalog.

[Chucko]

Right, FN810 is there to "catch" RPM drops well below requested idle. Good luck with the drive!

[d347643]

don't think I forgot about this thread. I had midterms and my laptop took a crap, blue screens of death so I can't datalog until I fix it. I still drive the car everyday though so I can still tell you three things I've noticed since I made the changes:

1. The rpms don't drop as low anymore when in neutral and coming to a stop. The two conditions I was experienced seem to have moved up in the rpm range if that makes any sense. The low rpm drop I have encountered now occurs about 950rpm now instead of below idle so there's no surging trying to correct. The car has also not stalled once so I feel this change was in the correct direction. Thanks again Chucko!

2. When I do come to a stop, the rpms settle a lot slower than before. I think this is because of the dashpot decay rate...no? When I'm stopped it will kind fo step down from 950 to 900 and then around 850 to idle. Before it would drop right to 850 when I was stopped.

3. The cold idle is also a little higher, this is probably because of the Dasmin and Daspto changes....

The next thing I plan on changing is leaning it out across the board. I'm suprised it smells so rich with a 331 and 24lb injectors @38 psi but who knows. When I start the car initially I notice there's more steam coming out of one tailpipe so maybe it's eating a little coolant or there's a vac leak or something.. This also may just be due to muffler angle and water pooling but I did notice that there's a slight amount of coolant coming out of the front of the lower intake gasket. I'm going to replace the gasket and weld a bung in my midpipe for my wideband because I trust that more than my nose.

thanks

Drew

[Chucko]

#1 - glad this worked for you!

#2 - Yep, that's the dashpot decay rate.

#3 - I don't think I made any changes that would affect cold idle. ???

I just started playing around with injector timing on my tune, and it made a big difference in the way the exhaust smells right after startup. I went with 240s in the area of the table where the engine idles, both warm and cold. All that extra time on the intake valve helps with cold idle quality. I can probably go a little leaner on cold idle now. You might want to give this a try.

[d347643]

a little clarification here. The dashpot decay rate affects how the rpms drops from the idle hang rpm to idle or across the board? Doesn't the daspto just act to decrement isc flow for each background loop? Also, the Dasmin acts to clip the isc when the engine is disengaged during declutch? I'm a little confused on that one still...

Drew

[Chucko]

Dashpot decay rate controls how the RPM drops at closed throttle. DASMIN is the desired airflow above the desired idle RPM when the car is out of gear and rolling but the dashpot has decayed all the way. DASPTO is the desired airflow offset to all dashpot calculations - I forget exactly which conditions this affects, I think it's when you get out and back in the throttle - but I found it necessary to bump up from stock in my tune. Not sure where you get the "background loop" in the DASPTO description.

[d347643]

The intermittent low rpm hang while coasting doesn't cause the car to stall anymore because it's around 950 but it still jumps back up right before coming to a stop. Would additional changes to the Dasmin fix this by allowing more airflow above the idle rpm while coasting?? Is it normal to have to modify these values this much?

thanks,

Drew

[decipha]

log during this condition and see what daspot is doing you'll know exactly whats going on then

[Chucko]

log during this condition and see what daspot is doing you'll know exactly whats going on then

What he said. Don't be afraid to log everything with the QH - it can handle the load, and you can always slim down the logging payload later, once you figure out what items are not useful for your combo.

It can feel like you're drowning in data, but after a few experiments you'll begin to see what's really happening. You can develop that insight without all the data but it takes a lot longer.

[d347643]

I mentioned before that rpm will still drop down to 900-1k when coasting to a stop and will jump back up to 1100-1200 before slowing to idle rpm. I attached a very short log of this condition. You can see how daspot is .14 and the duty cycle for the isc is about 42. I have a feeling the isc duty cycle should be higher and how the .14 value correlates with the .14 change that Chucko made. I don't know if its the dasmin or daspto yet but increasing the dasmin to a higher value would clip the isc during declutch. What's the right way to go about this? I can't believe I have had to mess with the isc so much!

Drew

[d347643]

looking at the datalog, theidle goes up with no change in timing, DSDRPM,ISCDTY,Lambses and I've found that its not dependent on MPH either Maybe this is some sort of adder doing this? Maybe the ISC Neutral RPM Adder? If that was the case then it should go back within 5 sec with a max addition of only 68rpm....hmmm, it jumps up about 250. The ISC decay rate that Chucko hooked me up with doethsnt have the tail at the bottom like the stocker either so I don't think that the decay is jumping up at the end either.

Input?

Drew

[Chucko]

Where are the ET and LOAD columns in this log?

[decipha]

if the engine is surging with no isc, spark, or fuel changes then you have a machanical surge, either the cam doesn't want to idle at that low of an rpm or you have a vac leak