What to adjust for stumble just off throttle.

[Mr DOHC]

Hey all.
355, dual plane manifold and a Holley 1000cfm TB here with a slight stumble as soon as you crack the throttle.
I know the car has a lean spot when you first crack the throttle, always has done which was sporadic. But seems to have gotten worse since the new big stall went in. Maybe since there is less load just off idle that it’s in a different part of the map. I dunno.

Anyway, what is the name of the table to adjust to change the enrichment for opening the throttle, and how much of a change should I make? Up 20% and see how it goes?

[antus]

sounds like that lean spot is the first problem. you dont say what pcm but try increasing the VE to fix the lean spot and it might fix the stumble as well.

[Mr DOHC]

Sorry. Holden VP with a $12p setup on it.

The car runs fine when cold and I can see via the AFR gauge that it runs around 13:1 at idle and it lean spikes when the throttle is opened abruptly (even tho it doesn’t open much). To me that points to an initial enrichment setting.

[immortality]

You want to increase the Acceleration Enrichment. AE table

It should be in the Transient Category.

[Mr DOHC]

I’ve just upped the 800r field from 1.00 to 1.1. See how that goes.

[antus]

If you've got wideband go WOT and look for 11.5 to 12.5 while it gets going to know if you're in the ballpark for AE.

[Deuce]

Hey all.
355, dual plane manifold and a Holley 1000cfm TB here with a slight stumble as soon as you crack the throttle.
I know the car has a lean spot when you first crack the throttle, always has done which was sporadic. But seems to have gotten worse since the new big stall went in. Maybe since there is less load just off idle that it’s in a different part of the map. I dunno.

Anyway, what is the name of the table to adjust to change the enrichment for opening the throttle, and how much of a change should I make? Up 20% and see how it goes?

I literally had the same issue over the weekend.
355" 4l60e, come TTB, at the drags, header extensions only (so bad AFR data without exhaust velocity up).
I'd hit the throttle and on the first run it stumbled and wouldn't burnout, and would launch and didn't start accelerating reasonably until 30kph+

Tried leaning the target area in 100kpa VE map and it got worse. So added a bunch of VE back in the area and it improved. Also looked closely (data tracing) at the cells between 80kpa idle and 100kpa WOT and lifted VE in those areas too.
Next run it did a burnout, stumbled on the hit, but I reckon it took off hard a few km sooner than previously.
Increased AE (quite a bit, roughly to 0.9 @ 2000 area) and it showed more fuel on the initial throttle stab, then lean, then sat in good AFR for WOT zone. So halved the decay rate of AE hit, (86 to 43 I think). It held better, but l later reduced the decay a bit further still.

All in all I believe it was an issue of:
A) big cam required low VE in the low rpm 90/100kpa zone (to stop it going in that zone, going rich and stalling out) and I had smoothed the map into the WOT area without any data of the area.
B) the high stall is lower than the cam's starting range, so about 500rpm of 'dead' area before taking off hard. And now I'm tuning an area it should realistically just flash straight past quicker.

I hope this experience helps you also.

[Mr DOHC]

My issue is around gently taking off from the lights.
If I VERY gently put my foot on the throttle until there’s just start to rise, then u can put my foot on the throttle and it’s fine. But if I jump from zero to even 7-10% throttle it stumbles and then jumps up in revs.
When you watch the logs it just goes lean then the AE kicks in and jump to 11-12:1 and off it goes.

One thing I noticed is when in traffic and coasting down a hill, when I go back on the throttle it was very bad. I worked out that under big vacuum, down in 20-30kpa, the VE table was very lean. So I bumped up those values and it made it way better.

To me that says my idle is way too lean and the manifold is dry of fuel as such, so when I hit the throttle there is no fuel left in the bottom of the inlet/back of valve and the AE takes a split second to richer it up enough.

Does that theory sound plausible?

[antus]

It does, but you might need to post up a log. There are a couple of factors that all could have something to do with it depending what you've changed and how. Without seeing all the data you might change the wrong thing and end up chasing your tail. Post the bin too if you can so we can compare to stock and see what you've changed incase something else is wrong and causing problems here.

[vlad01]

Don't forget there is a AE temp multiplier tables that scales the AE table depending on the temp. This is very useful when dialing in the AE based on the temp and warm up.

I had lots of outside of the box cam turning for idle, warmup and transients when I did a tune on an engine with a crow cam that had a wide LSA which was an eye opener, wide LSA cams turn out to be a massive PITA and hate everything to do with transients and warmup, cold etc...

Much easier with tight lumpy cams which are more forgiving and often work on stock settings for most things enough to drive. I found that tight LSA usually wanted a bit more AE and slightly leaner idle than a small OEM cam, but otherwise are not hard to tweak to perfection, but wide LSA cams want almost no AE and fairly lean idle and VE elsewhere, wide LSA also want really cut back warm up AE multipliers, idle AFR offsets and AE itself. Wide LSA I found stumbled heaps in lots of situations because what looked normal was actually too rich for it. Once I leaned the transients and most things out, it drove like OEM.

So it really comes down to what cam you have mostly and the rest are mostly secondary issues.