Low Vacuum at Idle - in the tune?

[dc_justin]

There are only 2 COS5 operating systems. 01290005 and 02020005. Both are 512kb OSs.
The 04 GTO uses a 1mb PCM. You cannot put a 512kb OS on a 1mb PCM.

You will not be able to use COS5 with your GTO unless/until Ross creates a 1MB version of that OS.

[gto_in_nc]

:(

Ross???

[Kevin Doe]

That's only 6"Hg of vacuum... that cam is big, but I would have expected a little more vacuum.

Edit: Hmmmm.... maybe that's all the vacuum you'll get.

You pretty much summed my thoughts up exactly. Everything else seems to be well, the VE table mapping is going well with the AutoVE. Did another few iterations. With each iteration I'm going to higher and higher rpm rows.

[Thimble]

My 240/244 111 cam idles around 70-75kpa at 900 rpm.

With your idle set at 800, 80kpa ballpark isn't all that surprising or unusual, and IMO the idle speed is a little too low for that size cam. Your kpa was right where I'm at while it was warming up and bouncing around 900 and 70-72kpa.

I have found my car's "sweet spot" as far as idle speed, it simply likes to settle into idle at 900 and does so reliably. I've tried 850, and although I can get to idle there, it hunts and stumbles a lot more than it should, much like you're experiencing, and it's just not worth the hassle to set it that low (or lower) and have to babysit it.

[redhardsupra]

i've seen 65-70kpa MAP from larger cams, so you might have a leak. dont expect this thing to behave well under 1000 rpm though. first make it idle at like 1200rpm just because it's much easier, and then try to make it work at lower rpm if that's what you want.

[mr.prick]

LOL i must have a really small cam.
i only have 40-45 kPa at idle.
and no it isn`t stock.

[RUTAN TA]

Im at 70-75kpa at idle with a 242/252 in a 346. It idles good at 850-900 at 25* and doesnt not ever surge or hunt at idle,im switching to COS5 soon.

[Bruce Melton]

I would take the 0-1200 rpm spark tables> idle, high and low octane- to a flat 24* all the way across. With your spark jumping around like it is, the idle will never settle in.

[SSpdDmon]

I would take the 0-1200 rpm spark tables> idle, high and low octane- to a flat 24* all the way across. With your spark jumping around like it is, the idle will never settle in.

x2

It shouldn't take more than 24~26* for that cam to idle in neutral. You may have to set the idle at 1,000rpm due to the amount of duration. That'll be tricky for fueling as it'll stick you smack in the middle of the two VE rows (800 & 1,200). I'd suggest running an OL-MAF tune. Using a WB, I'd probably target an idle AFR of ~15.5:1. If you're trying to get the car to work in closed loop, that may be part of the problem as you're more than likely flooding the engine with fuel.

Some other tricks you can do is to tweak the idle spark over/under correction tables and bump up the 0 & 400rpm base timing cells around idle. Check the old idle tuning thread in the tutorail forum stickies.

[Kevin Doe]

With my most recent tune I'm getting it in the 65 & 70 kPa cells. I'll post up the tune once I get a little happier with it.