I hate gen3 idle tuning.... cold start help

I am battling to sort out the cold idle on my stroked big cam (24X/24X) ls3 (cable throttle). I have got the BRA pretty sorted, I adjusted the IAC effective area a fair bit, it was way out (as well as drilled the throttle blade to get IAC readings around 60 at operating temp). I believe it must be one of the decay rates or something. If you look at the log when I fire it up its 26 seconds before it dies and I hit it again and its another 26 seconds and it dies again..... Im not sure what is up. It is also idling a fair bit above target when it first fires up for a while, not sure if that is due to after start enrichment. Not sure if the VE table needs tweaking, due to the long tube headers and cam overlap, the wide band is useless. Please help! im going bonkers!

can you post up a tune also

tune

Check your rail fuel pressure. Then work on getting your WB reading correctly.

Some Holden ECM's may reduce fuel pump voltage when the max torque is raised too high.

If you watch your iac position it is going crazy up and down quickly. What if you zero out your ect spark advance table correction up to like 212 degrees, change your in park spark table up to 1600 rpm at 20 degrees. What if you double the values in your adapteive spark under speed table. And closed loop enable ect vs iat to like 130 degrees. And your power enrich tps from 1600 rpm down to the same 45 percent also. What you want for the most part is for your iac to be pretty steady. You should also get the wideband working and use a commanded afr vs actual afr table going and dial in the ve table. Do you have real short exhaust after the wideband. The idle is higher at first because you have start up airflow added to the braf, which is what you want.

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Originally Posted by murfie

Check your rail fuel pressure. Then work on getting your WB reading correctly.

Some Holden ECM's may reduce fuel pump voltage when the max torque is raised too high.

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cheers ill log it

Exhaust is pretty long after the wideband, but there is a heap of reversion going on and giving bogus numbers at idle. You saying try to make sure its in OL at idle? Ill have a look at those other timing tables, there is no doubt the IAC is extremely erratic, do you think that is due to the fluctuating spark?

just looked at your iac steps vs effective area and I would change that back to stock. It should be pretty linear. I would keep it in open loop all the time until you get your ve table dialed in, then you could enable closed loop if you want after that. Once it is in adaptive idle it can change the spark and iac by how far it is off of commanded idle. For the iac it uses PID settings. So how ever you have those set up is how fast and how much it moves the iac in or out. I don't find the derivative useful but the proportional and intergral definately do. It takes a little bit of studying up on those to figure out how they all interact to get the idle sorted. Fueling is also real important. You should do a log with the wideband reading and post it up on here.

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Originally Posted by ryan_axberg

just looked at your iac steps vs effective area and I would change that back to stock. It should be pretty linear. I would keep it in open loop all the time until you get your ve table dialed in, then you could enable closed loop if you want after that. Once it is in adaptive idle it can change the spark and iac by how far it is off of commanded idle. For the iac it uses PID settings. So how ever you have those set up is how fast and how much it moves the iac in or out. I don't find the derivative useful but the proportional and intergral definately do. It takes a little bit of studying up on those to figure out how they all interact to get the idle sorted. Fueling is also real important. You should do a log with the wideband reading and post it up on here.

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hey Ryan, finally getting a chance to get a look at this idle problem again. Where abouts do find the proportional/integral settings for the IAC?

its under the idle tab, then rpm tab. bunch of different settings there

Disable STFT open loop. Unless you plan on passing emissions with that cam, having STFT OL enabled isn't going to help.

For those asking what the hell is a short term fuel trim doing during open loop...it is a little feature that manufacturers use to attempt to pseudo-closed loop control fueling before the O2 sensors heat up. This is done by monitoring the crankshaft reluctor wheel for misfire events following a cold start. The ECM detects partial misfires by watching high resolution engine speed - if abnormal crankshaft accelerations/decelerations are present and above a certain threshold, the ECM interprets this as poor combustion due to a rich or lean condition that the O2 sensors are still blind to. The OL STFT algorithm then steps in and attempts to trim fueling either rich or lean to improve fueling while waiting for the O2s. This of course requires precision calibrated misfire diagnostics - misfire in this file is disabled, not that it would be possible to calibrate anyway with a 240s duration cam. There really is no reason for anyone who uses HP Tuners to keep that feature enabled, so get rid of it.

And Ryan is absolutely right, derivative airflow must be removed as well. At least for the smaller airflow deltas. Derivative air can be useful to prevent stalls but you're better off leaving that correction enabled only for large airmass delta, definite-stall situations. In your case it's just disturbing stability.

Your in-gear idle airflow is not sorted, that still needs work. The base idle airflow, startup initial and friction initial airflow together are maxing out the allowed 40g/s desired airflow max value and causing the idle to hang at 1400 rather than falling to meet the 1200 desired idle RPM....despite the efforts of 14 degrees of start flare control spark retard. As soon as that flare retard releases and adaptive idle is enabled, it immediately maxes out the 8 degrees of overspeed spark retard because the friction airflow decay is too sluggish and the base idle air is still excessive. Meanwhile, the open loop fuel adder is ramping out too quickly causing leanness, ultimately stalling the engine...and the now maxed out idle underspeed spark table can't do anything about it.

Sorry to sort of rip into that a bit lol...just seems like a bunch of easily solved problems. Way too much idle air causing a chain reaction of crap for 26 seconds topped off by being far too lean with a cold engine. Big cams need a lot of fuel when they are cold and that setup is starved pretty good. Focus on that excessive air and lack of fuel and the rest of the small pieces should start to fall in line.

I had a similar issue my fix was (idle start up airflow vs ect) I added a .5 at a time and crept up on it . Yes there is way more to tune for cold start but this sounds really similar to the issue I ran into .