FireDemonSiC

I have something here I'm trying to wrap my brain around. I've tuned drivability, WOT and fuel economy. I am still however on the quest for that perfect idle. I thought I had it, until today...

Before, the IAC idle steps calibration was a little off. I would get zero steps with the transmission out of gear and the idle would hang at 1000rpm, with 900 being commanded. Obviously, the throttle blades were open past the point the ECM was able to control. In gear, the engine would idle at the commanded rpm and I would get around 20 steps. I got the tune to the point where everything was pretty much smooth as butter. Today, I attempted to properly calibrate the IAC. I fully warmed up the car, made sure the fan and A/C was off and adjusted the throttle stop screw until I was getting 5-10 steps at idle out of gear. Idle was now being correctly governed by the ECM. Re-adjusted TPS accordingly.

Took the car for a test drive and alot of the problems from my initial tuning process came back. Idle is now more erratic. The engine seems more sluggish to respond when coming to a stop. RPM seems to dip down to 700-800 and come back up, where before it wouldn't dip any lower than 850 (In gear idle is also 900rpm) and seemed much more responsive. The idle at a stop now has a very predictable surge. One second it will be idling fine then the next it will start surging. It keeps coming in and out on its own. It is very small. Maybe 50ish RPM but very detectable over how the car idled before the IAC calibration.

I am also thinking this has something to do with the fact that oddly enough, doing the IAC calibration seemed to lean the AFR out slightly. The very strange part is that the leanout was much more pronounced out of gear (With no change to the VE tables, went from around 12.5 to high 13s), however the erratic idle is much more prominent while in gear still idling around 12.7:1. Idle gets choppier with the leaner mixture which I like, but the idle becomes somewhat unstable. The IN GEAR AFR also seems to swing a bit vs before. While it was doing this, I noticed the IAC sitting dead nuts on 43 steps. The timing seemed to fluctuate by a couple degrees but nothing drastic. FWIW, I have all the timing cells from 800-1200rpm flattened to 25* in all the kPa areas she idles at.

Is there some setting in the tune I am overlooking or does this sound like a mechanical limitation of the engine somehow?

I am now strongly leaning towards putting the throttle stop screw back where it was or even better yet, having the IAC fully closed and adjusting the screw so it idles 100rpm lower than commanded in gear. Obviously this would cause the out of gear idle to be high again but if it's the only way to make this thing happy...

Before I do that, I want to make sure there isn't anything I'm overlooking or doing wrong. Attached is a screenshot of all relevant parameters that I can think of.

Engine and cam specs are in user info. 58MM throttlebody. Big siamesed SLP runners. Cam is a custom grind 110LSA.

RBob

iTrader: (1)

For port injection go for 20 - 25 IAC steps at idle. Which is also where it idled the best. The 5 - 10 steps is for TBI setups.

Running open loop idle has benefits as there isn't any proportional gains to deal with. Set this flag:

Option Word 1 - Bit 2 - OpIdl

The TF stuff for the IAC is throttle follower, which isn't used during idle, only when the throttle is being opened/closed. But it can help with the idle dipping too low when coming to a stop.

See what happens once the above is done, as that may clear a lot of this up.

RBob.

FireDemonSiC

Are you saying to adjust for this many steps in gear or out of gear? The setting I had before that worked GREAT was that many steps IN gear. Out of gear was zero and would idle about 100rpm more than commanded (Not a big deal).

Also, the tune has been set for open idle for quite sometime. I cannot do a closed loop idle successfully, as I begin to get surging issues
The VE is flattened to 40 across the 4 cells the engine idles at. Before this gave me an almost dead steady 12.7:1 at idle in gear. After IAC adjustment, it is now swinging around a bit between the 12s and 13s. What gives?

MrWillys

Depending on which ecm you're using when in park neutral it adds 50 to 100 rpm in the constants. I like to see between 40 to 60 IAC counts in gear at a fully warmed idle. Make sure you change your idle timing from 20 to 22 as well.

RBob

iTrader: (1)

It is in P/N with no other loads. Note that there is a P/N to Drive IAC bump that can be used:

IAC - Park to Drive steps

That is used to get the IAC into the proper position for the torque convert load. It uses the P/N input to the ECM.

Can go back to that setting. Easy enough to do. And the TPS voltage isn't critical, anywhere between .4 and .8 volts works.

I'm not surprised, way to hard to keep the AFR from over adjusting. On big cams too much of the mix goes right out the exhaust on overlap.

Poor air distribution between the cylinders.

RBob.

FireDemonSiC

The IAC park to drive steps I forgot to include in my screenshot. They are set at 10. Any recommendations? Verified that the EBL is seeing the gearchange also.

Poor air distribution...I was thinking that but wasn't sure. It might be best with this particular setup to put the IAC calibration back where it was. But I am open to suggestions to try before doing that.

Also interesting to know about the TPS voltage. I know that code reads the TPS voltage at each key on (From your tutorial of how to set the IAC and reading where you can key off for it to reset the TPS if it falls out of idle). Is this a feature unique to the EBL? I am used to the ECM just expecting the typical .54v at idle as 0%.

Also FWIW, the lift on this cam is fairly high. It's a roller motor that I did a split rocker arm ratio on with the airflow number on my heads in mind. Since it is a small bore motor, it will need to spin at a higher RPM to hit the same volumetric efficiency I would see on a 4"+ bore. With a 1.5 intake and 1.6 exhaust combination, taking the blueprint numbers into account the lift is at .534 on the intake and .570 on the exhaust.

RBob

iTrader: (1)

Whatever works. If the P/N to drive shift works with 10 steps, then use it. With higher stall of the convertor it isn't as critical.

Try it at 20 - 25 in P/N. If that works go with it. Can also go back to what it was originally as that too worked for you.

Different ECMs/Masks did the TPS voltage setting differently. The EBL checks the TPS voltage every time it is read against the saved "lowest seen" TPS voltage. And updates the lowest seen if the current TPS voltage is lower. This lowest seen voltage is used for the 0% reading.

RBob.

FireDemonSiC

It looks like I've got this idle on the ropes. Here is what I did:

- Took car for test drive and tried out various minimum throttle settings. Eventually settling on the correct 25ish steps at idle in P/N.

- Increased park to drive bump steps from 10 to 20. Not sure if that made any considerable difference but it certainly didn't hurt (Converter is a 9.5" EDGE. 3000 stall).

- Made some very small adjustments to VE. In P/N, I have VE adjusted to it is around 13-13.2 and a tad leaner in gear, around 13.5-13.8. Note that I did try taking a shortcut and changing the AFR vs RPM & VAC table from 13.8 to 13:1 in all idle areas. However, this also negatively impacted cold start fueling. The engine reeked of fuel, wideband was nearly pegged around 10:1 and the motor just flat out didn't sound like it was running well during warmup. So, I put that table back to where it was. I guess the VE is close enough at this point that I can just continue to modify VE and leave that AFR/RPM/VAC table alone.




It seems the idle problem is mostly AFR and VE related. I am going to try further increasing VE in the "in gear" kPa areas a tad and shoot for around 13:1. But, it seems like we can make this IAC calibration work.

I do believe a lot of this issue arises from uneven air distribution between cylinders at low RPM. I'm coming to accept the fact that I wanted to do a "Custom one off" configuration between the cam/intake and this is just the nature of the beast. The same thing that is causing that rapid surge at idle off a dead cold start. If you remember, I asked you about this awhile back. Nothing I have done seems to get rid of it. I've tried increasing VE in the cold idle areas, decreasing VE, flattening spark timing in all areas that the surge occurs (This did seem to make a small difference, however when the surge is occuring I can still watch kPa, IAC steps and timing all swing back and forth). I've also tried modifying the AFR vs CTS table. The most notable difference to this cold idle surge problem seems to be made by increasing the idle speed vs CTS table. That's the only REAL progress I've been able to make with that issue.

Anyways Rob, many thanks for the help. Any changes or beneficial corrections you can think of to further improve the situation, please let me know. I'm willing to experiment a bit.

FireDemonSiC

Any last minute input?

Tomorrow I'm going to flash the new tune and test drive.

FireDemonSiC

Thought I would give an update to this.

Ended up doing some research and changing a few settings around. I edited the VE tables to provide an open loop idle AFR in the high 12s. Also, regarding the swinging AFR. After doing research, it seems that adding idle advance on larger cams with more overlap helps to provide a more consistent AFR as the mixture is burned off sooner before exiting out of the exhaust valve. I increased the idle advance from 25* to 30*. I also tightened up the TF settings a little (I feel as if I had them set way too lazy before. As in, decaying very, very early).

Very occasionally, suddenly coming off the throttle when coming down to a stop it can dip as low as 750rpm before it bounces right back up off the stall saver, but about 95% of the time here is how it idles at a stop in or out of gear. This is with the standard 25ish steps at idle on a MPFI setup.

(Be sure to turn down your volume, as I wasn't thoughtful enough to mute the radio )

Any final thoughts?

RBob

iTrader: (1)

Video is set to private.

RBob.

FireDemonSiC

Fixed. Try again.

FireDemonSiC

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