Well, it "seemed" to idle better on the way back here, after the new IAC and making sure the throttle cable was not taut, but the numbers appear to contradict that in yesterday's log....(attached below)


I tried to add the graph to my HPTuners and had no luck, nor do I see where to actually add the numbers you circled? I'm a little busy here at work today, so didn't take a whole lot of time, but had zero luck

 

Here's the table for desired. Just copy this, add the filters if you want to, the filters are TPS and MPH. Plot this and fix your Base running airflow table, at least as a start. I have also noticed by setting the RPM too low, the desired can become as low as 3 g/s on an engine logging 15+ g/s when the PCM has trouble getting the idle physically down to that value.





Most of the time, the order for doing all this is:

1. Set RPM to a reasonable level so the engine runs well, typically gonna be a high setting to start.
2. Adjust RAF table to get enough air to run it
3. Adjust fueling to stoich (VE)
4. Adjust spark to drive MAP values down (more vacuum). When you stop seeing lower numbers, stop advancing it. Can be done in the scanner too and adjusted on idle spark tables.
5. Adjust adaptives, spark and air. Just adding in the % change in airflow is typically a good start point. These would be the Proportional (proportional RPM error), Integral (fine tune), and Derivative (fast acting change and stall saver).
6. Start lowering RPM down, repeat above as needed to stabilize it.
7. Adjust IAC as needed to correct dynamic vs desired error... THIS AFFECTS THE RAF.

Note with large cams, don't expect a 600 RPM to work too well. They are very inefficient at idle, so more RPM is needed to stabilize the engine and RPM.

I'm not saying you have to do all this, more throwing that up for others that might see it in the future as well. It's not set in stone as to the order, but that generally works. One thing that would help is if you could do an idle log, and make sure to add STIT (Short Term Idle Trims), LTIT (Long Term Idle Trims), and Desired idle RPM. That way we can see what the PCM is doing with the derivative and proportional airflow, and how it's acting with the IAC. Those are what physically control it based on RPM error. From there the PCM looks at the Base RAF table, then converts that number to effective area, which translates into IAC steps. All of that starts with error from RPM. If the PCM cannot reach a desired RPM, say like if you set the RPM at like 600 on a cam with 260* of duration @.050, it just can't do it. The counts will hit 0 at some point and you will see the "desired" drop down to like 2 or 3 g/s when the RPM is unreachable. This also has a lot to do with the throttle blade too... So as you see, can get complicated real quick lol.

So... All you really need to do is fix the Base Running Airflow (RAF), and then maybe bump the RPM up if needed a touch. Depends on the cam. Alternatively you can increase your idle spark a little to increase vacuum as much as possible. However you're already right about 62 kpa at idle which isn't too bad (mine idles at 70 lol, which is considerably worse).

Up to you on how to proceed with it. I've also found when you have that little ankle biter thing you're trying to fix, you might cause like 5 other problems trying to get it fixed lol. Sometimes it's best to get it to a good spot and leave it. Save your progress is all I can say with idle tuning. It's pretty hard sometimes.

Guess idle tune video will be coming soon... ugh. So not looking forward to that one. I'm still messing with math and formulas to actually figure out all the parameters at idle. No one seems to have any answers on that, formula wise. But as far as the conversion from RAF to effective area, it's basically: sqrt(step) = g/s, I think? Seems to work though, ish. Not positive as verifying this is really tricky, since the PCM will continue adding air over time as long as it sees an error. I've already dedicated hours trying to answer this today, that's as far as I've got so far lol.

 

Awesome stuff Chopper. Thanks for doing these tutorials, it really helps us beginners.

 

I appreciate, greatly, the help and insight you've offered and shared so far.

I made some tune changes, mainly in the RAF, Throttle Cracker, and Timing areas.

IAC counts look to be a lot steadier, and using the idle log info you posted, I logged my actual RAF, which is reasonably closer now.

Car is not all that radical...with a 6.0 and a 4L80E, along with a basic 228/230 585/585 112lsa cam, (900rpm idle, but hope to go to 800)

I attached copy of current tune and cold start idle log from this morning

Here is an idle vid from when I first did cam swap and did only minor tweaking

 

That looks a lot better now. Hells yeah lol. Sounds great too.

 

Thank you, and BIG thank you for the replies and guidance. Hopefully my thread-hijacking allows others to be helped as well.

I have had my HPTuners now for 11-12 years or so, but simply don't use it enough to stay current.

I'm going to do a cold start, in gear, datalog tomorrow (hopefully). If the numbers are as close as they are now...I probably won't modify it anymore...

 

ChopperDoc any guide on drive by wire vehicles?

 

Though I do have experience with them, I simply don't have as much as I do with the DBC cars. Primarily, the DBW cars seem much easier to tune in comparison, since there is no IAC at all... lol. I just didn't have as many problems with tuning DBW cars, which means I didn't learn as much. That and most have been Ford cars which are a different animal entirely. A few Camaros have been fairly quick and simple, even with cam swaps. I had a ton of issues using my car for learning and then follow on tuning experiments, which all comes back to "The more problems you have, the more you have to learn."

 

+1

Thanks again ChopperDoc for educating us here on the board! My car has a hard time starting (have to to 2 or more long cranks when hot). LS 427 swap on an '99 F body Gen 3 PCM.
I'm hoping with this tutorial put together with my current level of knowledge, as well as whatever else tutorials you have coming up, that I can get it figured out once and for al..

Thanks again!!

 

Stuff like this makes me tingle inside. I’m brand new to tuning just finished my first build got it started and I’m looking to start tuning it. I absolutely love your videos I’ve watched them all multiple times. I can’t express how thankful newbies like myself are for content like you posted @ChopperDoc you are an amazing human. Thank you.