hunting and flat spot at 1200 rpm

[Dazza92VP]

hey guys having a bit of a problem trying to determine whats actually wrong here but when at about 1200rpm under slight load like up a very small incline and with only about 8% throttle position it has a flat spot and wont accelerate untill ive cracked it further open but also some times instead of just a flat spot it hunts from 1000 to 1200 then crack it open its ok
vehicle is a vq stato with vs sIII maloo 5l v8 running 808 on 12p
the log is of it through the flat spot but it wasn't that bad when i took it

[Dazza92VP]

ok just managed to get a better log of it before the crappy battery in my laptop died but it shows it twice with an increase of tp% but no increase in rpm couldnt get it to hunt

[Holden202T]

well from what I can see of the very short log, your target AFR is lean, is it using lean cruise ?

the o2 voltage is nearly zero ... i'd be turning off lean cruise and see if this issue goes away.

if not then it will be a lean spot in your VE table you need to fix at that load point.

[Dazza92VP]

Yea lean cruise is on ill try again with it off today

[vlad01]

I got that same thing when the engine is cold on my v6, exactly the same as you describe.


Ordered a WB today as I can't tell crap from the narrow band. Also it evident I am running rich in some area and too lean in others despite what my target AFR and instant L/100km say. changed my plugs today, they were black lol.

I guess my stock VE table doesn't match my stockish engine?

[Holden202T]

Don't be confused, target afr won't make your fueling right it's just a number that is used as part of the calc, wide band will help you see what the actual afr is compared to target then you can adjust the ve table to make the two match!!

[Dylan]

Is it just trial and error to find what ratio the engine wants? Like with big cams etc.
Or is their a formula?

[Holden202T]

Generally you don't have to change the open loop afr table (target afr) you just need to adjust the ve table to get the two to match

[Dazza92VP]

Ok so found out it was the ve map had just one stupid spike at 1200rpm 65kpa so it's not hunting now and the flat spot is almost completely gone now its just down to the accel enrichment I'm pretty sure

[Dylan]

Generally you don't have to change the open loop afr table (target afr) you just need to adjust the ve table to get the two to match

So say comparing a standard camshaft and a large solid profile. And at (making up numbers here)
3000rpm the target afr is 14, with standard cam it ran fine with this ratio. The larger solid would run fine but would need help with the ve table to meet that target? Is my rambling clear as mud?