Ben.

Hi guys, just a quick question. Trying to sort out a nice stable idle, so my approach was to zero out my over+under speed spark tables, then use VCM controls to lock the IAC at the right steps, and lock the timing to 15 degrees (pretty close to right for my setup)

I thought by doing this I would eliminate all variables, and make small adjustments to fueling to get my idle right, but no matter what I do, I can't get a stable idle, it will constantly oscillate from 600-1200. Wideband reads pretty steady from 12.5-13, but I think this is due to placement.

I was talking to a fairly reputable tuner about my approach and his response was "yeah, thats just what they do", however I can't see why, logically, it wouldn't idle given the scenario.

I can only conclude that either my VE map, or injector data is incorrect, however, at this point all I want to know is, SHOULD it have a stable idle with IAC and timing both locked at reasonable numbers? Or does the PCM rely on spark corrections to keep it stable with my size cam at 800rpm?

for reference, cam is a 227/223@115, target idle speed is 800rpm, air fuel is around 12.8

Cheers,
Ben

kingtal0n

iTrader: (1)

flatten the area in your fuel map where the engine is trying to idle. Do the same for spark table. 15* is fine for now, but you may experience a slightly smoother idle with a bit more timing.

The idle A/F should be 14.5 to 15:1. Do not run richer than 14.5 for carbon buildup/economy reasons. All driving should be 14.5 to 15:1 except of course when demanding more from the engine (from about 8" of vacuum and up as you are probably aware should gradually richen up more and more all the way to 11.5:1 in street cars using 10-12psi of boost in most applications)

Now with the maps both flat in the idle area, and target a/f ratio displaying properly, check your output data (the "monitor screen" where it tells you what the engine is actually doing). Make sure the timing is steady and injector pulse is steady as well. If you notice that either one is jumping around despite the FLAT areas you programmed into the maps, then another map is affecting them and you need to find out which one.

Once you see that everything is steady, and notice that there is still a hunting problem, I would wager than you either have a vacuum leak, or a fuel cut programmed vs the tps set incorrectly. Disable or raise all fuel cut RPM controls and pressure test the air path to diagnose these two common issues.

In other words (in case you are wondering) the ECU might say " fuel cut RPM: 1200rpm" or something like that. I tune alot of different computers so I dont know which yours says, it is the setting that determines what RPM above which the engine will cut fuel when you lift from the throttle. If you unplugged your TPS sensor temporarily, it should disable this feature. It is mostly an economy feature, although there is some application when using an atmospheric bypass (not that you are turbo, just fwiw). Anyways, the engine might be taking in 1200rpm worth of idle airflow, and when the rpm hits 1200rpm the ECU checks the TPS and sees that you are not touching it at all, so it will cut fuel, and the RPM will fall back down, rinse and repeat = idle hunting.

Ben.

Thanks for that kingtal0n. being HPtuners, I can't flatten the fuel map, only the VE table, which will have an adverse affect on fueling.

decel fuel cut is deactivated.

kingtal0n

iTrader: (1)

You gota flatten the fuel values in whatever map you have access to so that the injector pulse does not jump around at idle. You want it to say consistently .877ms .873ms .875ms .882ms etc...

If its jumping around from 1.1ms to .887ms then that will cause stability issues. gota be fixed. Fuel has only a small effect on the idle quality (unless the cam is huge or ports are huge etc...) but for most 90%+ of the issue people have with idle is typically airflow. The iacv could be opening/shutting non stop trying to hold it still.

See this for setting the idle speed
https://ls1tech.com/forums/pcm-diagn...l#post19278875

1970camaroRS

iTrader: (8)

Dude, stop giving bad advice. You clearly don't know what you're talking about with HP Tuners and LS engine controls.

To the OP, you need to lean out and smooth the idle area of your VE table, play with your overspeed/underspeed timing, and most importantly, get the correct base running airflow. Search for the russK idle air config and rinkrat456's idle tuning guide on hp tuner forum.

ddnspider

iTrader: (26)

As said above, thats way too rich for a cammed setup to idle nicely. Lean it out to high 14, low 15:1 A/F and that also seems like not enough timing. You should be monitoring MAP pressure anyways for best idle. I bet if you lock timing at 20 degrees, 900 rpms, and lean it out to 15:1 it starts idling really nice.

kingtal0n

iTrader: (1)

Never touched HP tuners, only Haltech, AEM, Big stuff, MegaSquirt, Power FC, Motec, and a few others. They all work the same. HP tuners is not special, nor does my post have anything to do with HP tuners. You don't use HPtuners to set minimum airflow into the engine, you do it at the IACV Or throttle body usually, but I guess you don't know that?

Also, you never explained HOW to do those things you suggested. Its like the man asked "Hey guise, I am hungry" and you came in and said "oh you need to learn how to fish, go read about it". What a useful post.

My methods work for ALL those ECU I listed, because ALL ECU think the same way, plus or minus bells and whistles. I also took the time to explain HOW to do the things I mentioned, which you either do not know or do not wish to take the time to explain to the poor guy asking for help.

I wrote an auto-tuner from scratch when I was 17 years old for holley's first computer control injection system.
http://www.thirdgen.org/forums/dfi-e...der-950-a.html

I think that during the past 12+ years I have learned a thing or two since then, so where were you in the tuning scene 12 years ago? Programming auto tuners? Didnt think so.

1970camaroRS

iTrader: (8)

The post is a question from someone using HP Tuners so you answer is a way that isn't relevant? On an LS engine, you adjust the throttle blade very little and keep it within an acceptable voltage range. You adjust airflow and IAC using computer controls. For this you absolutely use HP Tuners to control airflow.

Instead of a wall of text repeating an answer to an already asked and answered question, I linked to where the answer is. Much more valuable than a copy & paste of an incorrect 2000 word essay.

Your assumption about ECU's is wrong. And because your answer was based on a false premise, the information you provided was wrong.

Writing an application in VB for an obselete tech doesn't impress me when we're talking about HP Tuners and LS motors. With your background and history, I'm actually surprised at how wrong and lost you are about everything we talk about here.

1970camaroRS

iTrader: (8)

Exactly. Find your common idle cells on your VE map and lean them waaaaay out. Then blend them into the rest of the map making sure adjacent cells are very close to each other. I agree commanding 20 is about right, but don't be surprised if you end up higher than that. Once you have that figured out, tune the running airflow using the RussK method and all that should be left is the overspeed and underspeed spark, throttle follower and cracker for low speed throttle changes and coming back to idle when stopping.

Darth_V8r

iTrader: (4)

OP, your cam can idle nicely. Heres some stuff that worked for me:

1. Fueling. Get fuel first or you're chasing your tail. Cammed motors with long tubes read false lean, causing computer to run rich at idle. Rich makes surge. The really very easy way to lean out your idle is to get your average idle air off the scanner - 10-g/sec is relatively typical, go to the tune and look up which airflow "mode" is 10 g/sec (for example) and then reduce the oxygen sensor switching point a bit. 300 mV works well. Typically you'll do this for zones 0-6. Then the computer will naturally trim your idle a bit leaner. Use your trims to adjust VE table.

2. Timing. Use the scanner. Put spark in manual control. Start with 20 advance. Increase timing and watch your map sensor. At some point your map sensor will bottom out and start increasing again. Let's say for example this is 33 degrees advanced. Then, subtract 8, gives you 25. Set all your idle cell timing values to 25. Then go to your over speed/under speed tables. Make your 200 rpm error 8 degrees and smooth all the way to zero at zero error. Don't have any values in these tables greater than 8.

3. Air. With the car good and warm, check your IAC is roughly 30 counts. If it's above 60, then turn the set screw 1/8 turn, do a TPS reset, and then start the car again. After it settles down to idle, check the IAC counts. Rinse and repeat until you get down to 30. For really big cans, I'll aim even lower, but your can is small with very low overlap. Then, shut it off and run the russk configure for idle air. Another thing you may need to do is adjust your derivative air. From 0 to 0.05, set the derivative to zero in both over and under tables. That helps slow down the IAC.

hope all that helps and makes a little sense

kingtal0n

iTrader: (1)

When you are saying counts, you mean step position out of 200+~? The other fellow is currently saying that from 0-15~ there is no addl airflow, and that 30 steps was no good. I can't wait to get my own LS engine to melt down and see for myself. Clock is ticking.

Darth_V8r

iTrader: (4)

Yes, steps is what I mean. The LS ECU reports motor steps. Think of a worm gear and an encoder on the drive side. The motor moves from one encoded position to the next - this is a step. Based on the ratio of the worm gear, this adds a certain amount of "effective area" to the throttle.

Here's an example to try to make the maths easier to understand:

The throttle is partially cracked and there is a small hole in the throttle, so the throttle behaves as if it was a 30 square mm hole. The computer calculates based on idle speed and other conditions that it needs a 34 square mm hole, so it references the IAC effective area table and determines that position 23 will result in a total effective area of 34, and then sets tells the IAC motor to go to step number 23. This is reported by the ECU as 23 IAC counts.

What tends to happen is the IAC effective area table is left alone or a simple move eight cells to the right is done - and rightly so for most scenarios - but sometimes you have to tweak that table, and it isn't straightforward, because you can't just log the two variables and populate the table.

What will happen sometimes is if you don't do this, you'll log for idle air, and it will always say you need 1-g/sec less than you're getting, and repeated logs keep trying to cut or add air.

Now, that whole post was WAY off topic for the OP's issue. Fundamentally, his motor is rich at idle, which causes surge, and probably needs more idle timing cammed LS motors like mid-20's and sometimes high 20's idle timing.

kingtal0n

iTrader: (1)

I've had lots of experience with the stepper motor on the TPI and TBI engines, and a Holley stealth Ram, and others. I just didn't think that LSx technology was still using stepper motors in this day and age. I expected something... newer. The old stepper tech seemed a bit flaky.

Darth_V8r

iTrader: (4)

FWIW, the general consensus on IAC counts is typically 30-60. There are quite a lot of idle subroutines that run. Even at dead stand still idle, you've got proportional, integral, and derivative air - classic PID loop - controlling the IAC motor. It has to be able to move in both directions to function properly. If it bottoms out, it starts cutting timing to achieve idle setpoint, which then makes off idle not as good. bottomed out can also cause a delay before the controller realizes it needs to open. So, yes, there is a need to keep it off the bottom.

There are spark compensation routines that run for over and underspeed, which are quite effective within about 150 rpm at controlling cammed idle surge. Some tuners will disable air adjustments within a certain band and rely on timing only when idle is 80 rpm or less away from target. Especially on an engine with really good throttle response that jumps in RPM with very little air increase.

Then, there are "return to idle" routines - cracker and follower. These serve to pre-emptively open the IAC during acceleration and coasting so that when you let up on the gas and close the throttle, it idles high and softly settle on idle vs undershooting and then overcompensating for the undershoot.

ALSO FWIW, the IAC is not the only thing that can cause idle stumble. Transition fueling can go too low on fueling, resulting in stumble - especially on clutch and coast after hard acceleration. Timing over and underspeed can be set too aggressively. No amount of airflow parameters will fix this, which is why you have to get fuel and timing right first.