That means my IAC effective area is way the hell off. I have mine cracked open and have a hole drilled in it. My desired air and dynamic/MAF air are off like 4g/sec. You can bandaid it though by just increasing the numbers in cracker/follower to be honest.

BUT! There's a limit. 84 mm^2 in the stock tune. Which if I left alone, means my IAC will never open more than 199 steps. And since I haven't touched that number, that's my magical "limit."

If I move everything over approximately 4 spaces to the right (which is 1g/sec for me when I log IAC steps by MAF airflow - every 4 steps is about 1g/sec), I'll be into the zeros about 22 cells in. Which means I'd have to update the 84mm^2 max to much higher. But that's okay. The issue is the IAC will never crack open. Because now, it seems to find the IAC lookup around 30-32mm^2 which is about 50 counts hot. Maybe then I would need to up my idle airflow?

You know what, I did move my IAC effective area over about 6 cells. And I bumped idle airflow from 5.8g/sec to 7.4g/sec and it still idled at 50 steps. So that's probably why my idle airflow is so damn low vs stock. Push it over another 12-18 and it probably goes up another 4-6g/sec for the calculation and remains at 50 counts. I don't know if it even matters. You just gain some granularity with the IAC steps. If the PCM commands 12g/sec and wants to add 1g and it picks something 12 slots to the right. What's the difference from commanding 7g/sec and it wants to add 1g and it picks something 4 slots to the right? It still adds 1g/sec. But I don't know - that's bad practice if you know something is off it just makes everything else spiral. If it wants to add .5g and it thinks going 4 is .5g and it's really 1g, then you're off half a gram. That could be a slight issue. But then you just tune out half a gram in the follower/cracker. So I've gone in a big swirling stream of conscious loop. But I'll still try it.

I can always go back.

 

Somehow I ended up with some creative logging figuring out that 16 counts was roughly 1-g/sec on mine. I was being conservative so I subtracted 32 from the entire table, and it got closer. I can't remember how much total I ended up off vs stock, but it's pretty far.

And I went through that same loop you did Jake. Why does it matter?

The computer can be commanded 7, realize it needs 9, and trim up 2 and be fine right? Yes. But on a return to idle, it starts with commanded air. If you're commanding 7, and itvreally needs 9, it has to figure that out every time.

Same scenario, but you get commanded matching actual, when you need 9, you also command 9, so it gets there quicker.

At least that's how I THINK it works

 

Change it.

 

That's exactly how it works... idle trims only work at idle, and the transition to idle can be a bumpy ride when the airflows don't line up.

 

Thanks.

Haven't had a chance to play with the car this week. But maybe tomorrow night. I have the tighter VE table now, cleaner cracker airflow, revised IAC Effective Area table, and pulled back from 6.2 on EOIT to 5.85 and returned to stock levels when cold as you want to spray earlier not later. That may allow me to lean out the 1200 column some. We shall see.

 

My philosophy on idle air is, put a bit more than you
need in the table and let closed loop RPM pull it down;
never put the minimum (or even final closed loop) in
the table because it's the first guess. Especially if you
see idle fuel trims wandering around, pad the airflow
to make sure trimmed-fat has enough to not let it
undershoot, put you onto the 400RPM column where
you haven't got well tuned VE, and maybe choke out.

 

I will say this. Had the car out today (in the 60s, yay) and it seemed to do better with those changes. The VE table was off, but it gave me a new baseline.

Changing the EOIT means that I had to add back in a lot of fuel at the bottom. The idle was more stable however. I had pushed the EOIT back too much. The fuel smell was better, and I was able to idle at stoich in SD OL for the first time ever with this cam. So I feel like that was part of the issue. I still have more tuning to do there. But it's better.

The other major change was to the IAC Effective Area. I needed to increase the Base Airflow by around 5-6g/sec. So now the base airflow table looks like other cammed cars. And now my desired idle, dynamic airflow, and MAF airflow are all within 1g of each other. So now the revised Cracker table can control the idle. I may have a little bit too much air in there and may take out .5g/sec to see - not really cruise control effect, but I'd rather have something that feels close to than than getting dips.

Those two things made my tune look more like other tunes I've seen. And reminds me of something Geoff Skinner told me - don't mess with tables in the tune unless you have to. They are control tables set by GM. It almost feels like the EOIT table is something like that, but it helped a lot with the bigger cam. And hurt some with the smaller cam. I had thought about going all the way back to stock, but I knew when it's done right, it does help with fuel smell and off-idle power. I think I'm pretty close by backing off Normal to 5.85 from 6.20.

As far as the oscillating/dips... with the MAF, it's completely gone. And in SD OL it's pretty much gone. The only time it shows up is SD CL... or Blended SD/MAF CL. So I don't know what to do there. I'm moving in the right direction.

 

Good to hear. I look forward to examining your next tune. I found Darth's explanation of the IAC tables, and how they are affected by drilling the TB, very informative.
Unfortunately we now have 8" of snow and no change to experiment. Actually I already have the car apart for the planned winter projects.

 

Yeah. I think it's a good change. Even though I had tuned it to idle around 40-50 IAC counts... tuning that table more accurately and then adding all the base airflow brought everything more in line.

I'll post my latest tune and logs tonight.

I'm also going to play with my VE table to clean it up. I was just applying "paste multiply by 1/2" to make changes.

 

Nice! This thread might make a really good one to bookmark. It's not had a lot of views but really good stuff in here

 

Tune as promised. Don't have a long log with this. So I'll take one tomorrow.

There is good stuff on the IAC effective area tuning... EOIT caveats for the Gen III PCM... and well, the spark tables are pretty solid. Folks could use those as baselines.

 

This is a good thread.

 

Yes, I plan to make it a sticky by creating a sticky section called something like "Tuning for Cams" and putting this and a few others in that section.

 

This thread has made me start toying on mine again - I know, don't fix it if it ain't broke - and I did run into something else worth adding to the list:

First start, about a week ago, I started getting no charging from alternator. Reach down in there and wiggle the wires around, it starts charging and the engine immediately starts stumbling, etc, takes a minute or two to stabilize. Hell of a coincidence it started doing this on the same day I started playing with idle settings again. Runs fine when not charging ironically.

So yesterday, I decide to see what's loose and the stud you nut the charging cable to is loose. Yay. Found it. Tightened back up, reconnected everything. Start it up. No charge.

I had previously lengthened the exciter wire - so I could work on it without breaking it. I started tracing it back, and the wire fell out of the connector. With the pin still inside it, which had broken off of the alternator. So, now I got no charge at all.

But point being, voltage fluctuations off the alternator are a huge contributor to idle oscillating. So much so that if the alternator is the problem you can't tune it out. Imma convert to a one wire alternator that just puts out a constant 14.5 volts.

 

Darth, your posts don't show up again. We gotta look into that.

I upgraded my big 3... all my TPS issues went away.

 

****. OK. I did figure it out, its the phone app I use. Here's what I posted before. just in case:

 

Darth: Your tune being sensitive to alternator voltage makes me wonder if your injector data is correct, especially the huge "Injector Offset vs Battery Voltage vs KPA" table. Did you get the full data with your injectors? I've also had alternator problems that varied my system voltage between 12V and 14V, but it had no effect on the tune or idle.

 

The tables were copied over from deatschworks excel file for their 39 pound injectors, which is what I run. I thought something similar myself but I just don't want to adjust any tables like that from the provided data.

It was very stable before that thing started acting up. And is not voltage fluctuations so much as randomly "charging, not charging, charging again!" Prior, it handled voltage fluctuations fine. This is different. Yes voltage changes but also engine load randomly changes

 

That data deatchworks provides is not reliable from what I've seen.

 

I'm getting ready to rip these out and revert to GM factory injectors like the 42 lb truck flex fuel injectors. I'd drop to the 36 lb GTP injectors, but the 39's are at 80% duty cycle already. However, this is

I'm quite confident I'll get the new alternator in and it'll be back to stable.

I'm quite surprised you had such good results pulling the EOIT table all the way back to 5.85. I wouldn't have thought that'd make such a big difference. And you're saying you actually reduced the fuel smell? How much overlap is in that cam? your old one had 16 degrees IIRC?

Sort of re-read jimmyblue post, and I think what he said clicked. Almost like using the base airflow as a built in cracker. You drop to idle, it starts there, and if it's a bit high, it trims down accordingly through closed loop. That might explain one thing I've noticed on mine - I always got better results doing that cold start / idle config thing and using dynamic air instead of commanded air, especially before I figured out the IAC table. When I started messing around with my other vehicles, I've found that it always seems to do better using dynamic air on a vehicle that I haven't worked the IAC table. probably the same philosphy?