pcmhacking.net

This has been mentioned before, but I'm not quite clear on the details.
VN Commodore
The correlation between 'Idle spark advance' and 'Main spark advance'
These tables are completely different on my bin (I have been playing around a bit). I assume they should matchup. But what engine speed is "idle". I have a rather lumpy cam and at the moment idle is loping very badly between 700 & 1200. For some reason the tacho wont go under 1200 at idle, yet falls to zero with engine stopped (sticky?), so I'm only guessing.. I thought if I got this bit right it might help.

The idle spark is used when the throttle is closed and vehicle speed is less than 5kph. The idle spark does not have to be identical to the main spark table but having them close means you dont feel the transition.

Because I'm using a Getrag box, I haven't interfaced a speedo yet. Does that matter? I assume it always shows 0 kmh.
Quote "The idle spark is used when the throttle is closed". If I've adjusted the base idle will the TPS still show throttle closed? If the Idle spark table is only used at closed throttle, why do the load parameters go up to 95% ?
My maps look like this
Idle Spark advance is 10 at 100% and 30 at 20%
Main spark is 15 at 100% and 24 at 20% around the 1,000 rpm region
Should I change the Idle spark to similar figures. Or is there someway to disable the Idle spark advance table and just run off the main spark map.
It's a purely competition vehicle, so perfect idle is not critical, just a bit better than what it is at the moment.

have you increased the idle to suit the engine mods ?

one of the biggest issues you will get if you haven't is that its trying to idle at the stock rpms and because of the bigger cam it just isn't happy so it starts hunting up and down the revs, this just starts sending everything off .... IAC trys to compensate spark is always changing and you never get a smooth idle.

theres no reason you need to stop using the idle spark table, but easiest way to fix the problem is to change the 800rpm and 1200rpm (or 1000rpm if $12P etc) spark advance so its the same as whats in the idle spark table ....

getting fuelling at idle right will help alot too....

oh and if you haven't done it you'll probably need to increase the desired idle rpm

with a lumpy cam you want no less than 20 or 25 deg at idle, that will help smooth the idle heaps as lumpy cams tend to idle around 75 kpa

Thanks guys, I'm really getting somewhere now. I plugged in my new A/F meter, which only confirmed what the black smoke said. Idle mixtute around 10 to 1. I needed to reduce the VE in the area (idles at 1,000 and 60 kpa) from 68% to 44%. I took it for a drive last night with A/F and vacuum meter connected and still shows 10 to 1 in some areas, but I can gradually clean that up. I just orderd an Eeprom, can't wait for that, will make everything so much faster.
I can understand the 'hot' cam ruining low down efficiency and so a rich mixture and conversley I would have expected higher revs to be getting in more air and so run lean, But still runs at 13.0 around 5,000.
I also believe I've disabled closed loop by removing all reference to 14.7. Is that right? Just want to make it as simple as possible at this stage.

rather than removing all 14.7 find the scalar stoichiometer afr and change it .... whatever number you change it to is what it will go into closed loop at....

also not definate, but if you are not seeing increased efficiency at higher revs then it may be that the head isn't flowing enough so hense less efficient!

do you have cam specs or part number etc ?

The cam is 285 duration, Pacemakers, 10:1 pistons, balance shaft gone and my own head job which is a general opening up of the ports and removal of valve guide protrusion into the ports.
I'm quite happy with the result of the engine build. I need to play the throttle to control wheelspin in 2nd gear. It wouldn't do that before. That's with rally tyres, good street tyres may be a bit different.
I'm running off a Marobi bin as the base tune, which I believe is very rich at the top anyway, which might help explain the OK a/f's at wot.
So I'll make the stoichiometric a/f 16 and shouldn't need to think about closed loop again.
It's been a long struggle learning this new way of tuning EFI, but with help from this forum it's finally paying off.

marobi chip biff that in the bin and start from scratch with a totally stock tune to save the headache .much better starting totally stock

sounds like you've done the right stuff to it then ... be interested to see what sorta power it makes in the end!!

have you noticed any adverse effects of the balance shaft ? i removed mine when i rebuilt the motor but since then its only been in and out of the shed a few times so i have no real idea how it will go.