Idle tuning issue

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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Wiggles93
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Idle tuning issue

Post by Wiggles93 »

Hey have a bit of an odd issue, just put a cam and ported heads on my l67 vy, and now at idle and only at idle it sits for a moment at 14.5-14.7 then the fuel trims start leaning it right out past 16-17afr and I cant figure out why.. currently disabled closed loop till above 1200rpm to stop it happening but I feel like it's a poor fix
O2's seem to be doing the right thing and fuel trims anywhere but idle are working as they should, could this be an issue caused by the motor now not making enough vacuum at idle for a setting I've missed?
Shhh, it hasn't broken yet
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hsv08
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Re: Idle tuning issue

Post by hsv08 »

How big the cam?

Large overlaps and reverberation don't like airflow meters.
Wiggles93
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Re: Idle tuning issue

Post by Wiggles93 »

It's 222* intake 232 exhaust 113 lobe separation and if I remember around 2 degrees of overlap
Surely a "little" reversion can't spike the fuel trims to Max? It's fairly steady around 14.7 until stft takes up to its 20% Max fuel reduction
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vlad01
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Re: Idle tuning issue

Post by vlad01 »

it will be more than 2º overlap, more like 60º
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hsv08
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Re: Idle tuning issue

Post by hsv08 »

Wiggles93 wrote:It's 222* intake 232 exhaust 113 lobe separation and if I remember around 2 degrees of overlap
Surely a "little" reversion can't spike the fuel trims to Max? It's fairly steady around 14.7 until stft takes up to its 20% Max fuel reduction
There will be more than 2 degrees of overlap with those durations.

Whats your idle AFR set as?

Is it dropping into closed loop and trimming that fuel out, or is it going open loop and the AFR on wideband goes 16-17:1?
Wiggles93
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Re: Idle tuning issue

Post by Wiggles93 »

Overlap is, in degrees from exh closing @-1.8atdc to intake opening @4btdc so 2.2degrees?
It sits steadyish around 14.6-7 but as soon as it enters closed loop it starts pulling a heap of fuel
What's odd is the narrow band o2 is showing that it's running lean aswell, but it's still pulling fuel.. have tried another o2 sensor with no difference
Shhh, it hasn't broken yet
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hsv08
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Re: Idle tuning issue

Post by hsv08 »

Wiggles93 wrote:Overlap is, in degrees from exh closing @-1.8atdc to intake opening @4btdc so 2.2degrees?
It sits steadyish around 14.6-7 but as soon as it enters closed loop it starts pulling a heap of fuel
What's odd is the narrow band o2 is showing that it's running lean aswell, but it's still pulling fuel.. have tried another o2 sensor with no difference
Can you post your cam card? Still doesn't sound right.

Also perhaps your tune file And a log?
Wiggles93
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Re: Idle tuning issue

Post by Wiggles93 »

My laptop doesn't want to play the internet game so I can't post anything useful at the moment..
The cam is a csbr 523 from come racing, the specs come up when googled
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'quipt4it
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Re: Idle tuning issue

Post by 'quipt4it »

Yeah, I thought those figures of 2.2 degs. overlap were at 0.050" lol.
Your timing events are 35 71 int. and 86 32 exh. if installed 'straight up'.
67 degrees o/lap @ adv. duration.
Added:
Find the Injector Rate Constant Vs mg/cyl Vs RPM table (50-850 mg low boost). Use this table to adjust the idle and/ or off idle.
Track the lean areas that need extra fuel when logging, then view bubble tracing in the table and adjust those areas to suit.
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