Lean stumble with hard rev from idle, help
Lean stumble with hard rev from idle, help Hello everyone, I've been working on the tune in my cammed 02 camaro for a while now and it's finally starting to shape up, except for an issue where when you give the throttle a good whack from idle instead of revving out cleanly it goes super lean as confirmed by wideband, sputters and will lean pop as well, but if you slowly give it throttle it will happily build rpm, or if you build the rpm up to say 1500 first and then give it a quick shot it will also rev fine from there, just not from idle. So I was wanting to see if someone could point me in the right direction to which table or tables in HP tuners I should looking towards I would greatly appreciate. Thanks
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I'm guessing the VE needs to be increased in the low-RPM + low-vacuum area.
If you can data-log RPM, MAP, and AFR, that will give you a clearer idea of which cells to adjust. Keep in mind the AFR sensor might need a bit of time to react though - for best results you might need to look at the RPM and MAP one or two rows above where you see AFR reading lean.
If you can data-log RPM, MAP, and AFR, that will give you a clearer idea of which cells to adjust. Keep in mind the AFR sensor might need a bit of time to react though - for best results you might need to look at the RPM and MAP one or two rows above where you see AFR reading lean.
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From: Virginia
I'm guessing the VE needs to be increased in the low-RPM + low-vacuum area.
If you can data-log RPM, MAP, and AFR, that will give you a clearer idea of which cells to adjust. Keep in mind the AFR sensor might need a bit of time to react though - for best results you might need to look at the RPM and MAP one or two rows above where you see AFR reading lean.
If you can data-log RPM, MAP, and AFR, that will give you a clearer idea of which cells to adjust. Keep in mind the AFR sensor might need a bit of time to react though - for best results you might need to look at the RPM and MAP one or two rows above where you see AFR reading lean.
I agree we need to see numbers to assess it, since after all we can’t see a damn thing and all of this is speculation without a log or two to support it.
I appreciate your reply though and I agree with your assessment overall. We don’t freaking know lol.
I appreciate you guys replys, DFCO is turned off and I was kind of thinking it was possibly a transient issue I'm just not sure on which one or way they should be tinkered with, I have seen some mentions of a "stomp comp" table but that seems to be an efilive thing and I'm not seeing one in HP that would be the same thing, I guess it would be to easy if there was a table like that, lol thanks, I will see if I can post a log from work, I only have my phone for internet at the house.
Another note, and reason I am suspecting the transients is after a rev on return back to idle my wideband swings from being lean with rpm going up to rich on return to idle. The only transient I have adjusted is the minimum mg.
Here are 2 logs, one showing a few hard wot revs and the other showing the slower revs. There is some idle instability caused by me making the tune a bit rich from what it normally likes just to see if that would help.
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The rest of the table could be perfectly dialed in, but if 1000 RPM @ 100kpa is lean then I'd expect the behavior the OP described.
Tip-in compensations exist in some car to address similar scenarios, but if stomping the throttle from higher RPM doesn't go lean, then this probably isn't a tip-in problem. Unless there's a tip-in table that has an RPM axis so it can be tailored at low RPM without affecting higher RPM.
I went looking for tip-in tables in TunerPro just now and didn't see any, but that doesn't mean they don't exist. Maybe it's called something else in the GM world, or maybe the XDF is incomplete, or maybe I'm just looking in the wrong place.
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Verdad Gallardo TECH Fanatic
Joined: Oct 2014
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From: Virginia
If you stomp the accelerator at idle, you'll hit cells in the VE table that never get used under any other conditions.
The rest of the table could be perfectly dialed in, but if 1000 RPM @ 100kpa is lean then I'd expect the behavior the OP described.
Tip-in compensations exist in some car to address similar scenarios, but if stomping the throttle from higher RPM doesn't go lean, then this probably isn't a tip-in problem. Unless there's a tip-in table that has an RPM axis so it can be tailored at low RPM without affecting higher RPM.
I went looking for tip-in tables in TunerPro just now and didn't see any, but that doesn't mean they don't exist. Maybe it's called something else in the GM world, or maybe the XDF is incomplete, or maybe I'm just looking in the wrong place.
The rest of the table could be perfectly dialed in, but if 1000 RPM @ 100kpa is lean then I'd expect the behavior the OP described.
Tip-in compensations exist in some car to address similar scenarios, but if stomping the throttle from higher RPM doesn't go lean, then this probably isn't a tip-in problem. Unless there's a tip-in table that has an RPM axis so it can be tailored at low RPM without affecting higher RPM.
I went looking for tip-in tables in TunerPro just now and didn't see any, but that doesn't mean they don't exist. Maybe it's called something else in the GM world, or maybe the XDF is incomplete, or maybe I'm just looking in the wrong place.
Carburetors had such a simple solution to this complex problem. Ye Olde Pump Shot.
In the fuel transient tables, wall impact factor gain. Multiply your 100 kpa row by 1.2. Then blend it down to your 50 kpa row.
Do not overdo it. If you see your lean spike still there, but less bad, do a 1.1x and blend. If you see it went rich tip in, do a 0.98x and blend.
I do also tend to push the VE in the high load (low vacuum) off idle tables also to compensate for the missing pump shot. My VE tables from 1200-2800 in the 85-100 kpa rows are almost horizontal typically.
In the fuel transient tables, wall impact factor gain. Multiply your 100 kpa row by 1.2. Then blend it down to your 50 kpa row.
Do not overdo it. If you see your lean spike still there, but less bad, do a 1.1x and blend. If you see it went rich tip in, do a 0.98x and blend.
I do also tend to push the VE in the high load (low vacuum) off idle tables also to compensate for the missing pump shot. My VE tables from 1200-2800 in the 85-100 kpa rows are almost horizontal typically.
I looked at your logs, it's pretty easy to see where it goes in the VE table.
The wideband is always a little slow, but the map logs pretty fast.
In all honesty, HPT scanner certainly can be suspect depending on how many parameters you log and what gets set as priority.
Need to make sure the polling interval is set to the fastest it will do.
At any rate I would try increasing the VE in the 400-1200rpm columns in the high map areas first.
BTW, if this is a stick shift car, you can hit those areas pretty easily using high gear, or even third by rolling along at idle and slow pressing the gas pedal. You can hit those cells much like being on a loaded dyno. if the car doesn't get too pissed off in those areas.
Would be interesting to see your tune.
I've not messed with the transient tables, But thanks Darth and Chopper, i will look into this on cars I tune when the owner insists on having crisp throttle whacks.
The wideband is always a little slow, but the map logs pretty fast.
In all honesty, HPT scanner certainly can be suspect depending on how many parameters you log and what gets set as priority.
Need to make sure the polling interval is set to the fastest it will do.
At any rate I would try increasing the VE in the 400-1200rpm columns in the high map areas first.
BTW, if this is a stick shift car, you can hit those areas pretty easily using high gear, or even third by rolling along at idle and slow pressing the gas pedal. You can hit those cells much like being on a loaded dyno. if the car doesn't get too pissed off in those areas.
Would be interesting to see your tune.
I've not messed with the transient tables, But thanks Darth and Chopper, i will look into this on cars I tune when the owner insists on having crisp throttle whacks.
Thanks to everyone that responded, looks like you were all correct, I ended up adding to the ve in the high map areas and blending down to just above my idle map region from 400 rpm up to the 2800 rpm area and then added about 40% to the transient. All of this netted me a nice clean rev with a wide open throttle hit from idle to as high as you want to rev it. Thank you guys again. Michael