hodge9386

iTrader: (5)

I am running a SNS stage 3 235/243 .631/.610 with a ported ls2 intake, ported ls2 tb, longtubes, cattless x pipe, mildly hand ported 243 heads. 99% of my tune is good, it will drive part throttle in 6th gear at 45mph with no bucking, wot is good, it even comes back to idle without searching or any of that crap. The only thing that is bugging me is the actual idle, I want a nice even steady chop but it wont do it. It will start to idle nice and steady then it will sound like its fighting with itself and the engine and car will start shaking. The idle dosent search, it stays right around 900 rpm and my spark is steady at 25/26*. Iv tried close loop idle at 14.7 but my o2 sensors are very erratic so i thought the 17* of overlap was causing the o2s to throw my idle off so I tried open loop and leaned it out to 16.3 which it seemed to like but it still kicks into this quick chop/struggle and shakes the car. Im not sure what to do with it anymore. Any body have some suggestions?

My tune is attached.

JakeFusion

iTrader: (7)

That's what 17 degrees of overlap will do.

I have basically the same cam. Increase timing at idle until the shake is gone. I am at 32 degrees in gear. It's pretty smooth. You could also raise the idle to 950 or so.

I have mine set at 900 and it doesn't shake like crazy with the timing.

You just have to make sure you match you main spark tables if you increase your timing significantly or that will cause a buck as you return to idle. I know I actually have my timing in idle at 32-34 to match my main spark. Big cams are supposed to want less idle off-idle, but I found my drove nicer with more timing.

Also, 16.3:1 in OL is good. Big cams love to idle lean.

hodge9386

iTrader: (5)

ok ill try that.

another thing is how exactly does the idle spark advance work? mine is set to around 8* in the areas where it idles but my scanner is saying 26*. Does something add with it to get the final timing?

hodge9386

iTrader: (5)

Never mind I figured out the idle spark. The table is not kpa. I set it to 30* and the exhaust pinging went away but it still does the quick chop a little but not bad. I'm just going to have to live with it.

JakeFusion

iTrader: (7)

That's just the amount of idle spark added or subtracted from base spark to hold idle steady.

subeone

iTrader: (5)

Holy batman 30* degrees of timing is too much you generally want less ignition advance with more overlap. I've had 416s with 25x/26x duration bump sticks idle fine with 10-15 degrees of base idle advance.

JakeFusion

iTrader: (7)

Did you add timing to those motors? Did you watch the kPa drop as you added timing? It may idle fine, but the more timing you add the more vacuum the motor will create to a certain point. Then you back off a bit to maintain just enough. It'll also smooth out the motor.

Plus, it depends on the combo. Different heads respond to timing different as well.

hodge9386

iTrader: (5)

I know my car had some exhaust ping at idle with 26* and it stopped and idled better with 30* so that's where I left it. It's a faster chop but it is steady and I have less raw fuel smell. I may try to drop the idle down just a little but im leaving it where it is timing wise.

JakeFusion

iTrader: (7)

You might try adjusting your EOIT settings under fuel... Normal is 5.45... try it around 6.25 with that cam (across the board). By delaying when the injector fires, you'll fire onto a closed valve vs an open one (cam timing has been delayed vs stock with the cam and adjusting injection timing will help with fuel smell and overall smoothness).

You will have to adjust your VE table after you do this. You'll be running richer. You'll be spraying less fuel directly out the exhaust and more will end up in the chamber.

subeone

iTrader: (5)

^very well said, many people have proper AFR's but still have a raw fuel smell and dont realize that the end of injection timing has to be adjusted accordingly.

Also, you can't possibly be pinging at 26* at idle. Let alone not ping with more ignition timing. Just some corrections, but if it runs good then "if it aint broke dont fix it"

hodge9386

iTrader: (5)

My eoit settings have been adjusted. I'm not saying the car wouldn't idle at 26* or even at 15* but this cam likes to idle lean with 30* of timing. I know it's not the norm but it's what this cam likes.