custom os and idle

[minytrker]

I have a fairly large cam in my car and just went with a custom os and did the whole tune. The car ran great and idled perfect. Now with without changing anything the car wants to surge at idle. My a/f is still on the money. The only thing that changed is the intake air. It was about 20 degrees cooler when I did the tune. What am I missing?

[Blacky]

Air conditioning on/off?
My idle was rock solid with A/C off but surged up/down about 400 rpm with A/C on. I reduced the A/C parasitic torque {G0108} and {G0109} (both tables, entire table) by -75% and that cured it.
Paul

[minytrker]

It does it with both but the ac makes it worse. I drove the car tonight with the intake air 20 degrees cooler it idle better but not like it did the other day.

[TAQuickness]

sounds like the b4307 may be off a bit.

When the car is idling, what are your IAC steps at hot idle?

How do your BEN's/AFR's look at when the idle surges?

[oztracktuning]

They idle much better richer than stoich... at least mine does.

[minytrker]

sounds like the b4307 may be off a bit.

When the car is idling, what are your IAC steps at hot idle?

How do your BEN's/AFR's look at when the idle surges?


IAC is 310, I didnt mess with that. My a/f is just a little lean its 14.88-14.98 at idle. Im going to try to add some fuel today and see what it does.

[caver]

You will never get a cam to idle decently at those afr's You need to get it down into the 13.8-14.2 range and maybe even richer. Remember your wb is not very accurate at idle with a big cam.

[TAQuickness]

I dunno. My 238/242 likes an idle AFR around 15:1.

your IAC at 310 is more likely the culprit in my mind. At 310, the IAC is all the way open and can no longer add the extra air you need for idle. You may want to try adjusting the set screw or enlarging the TB blade hole just a bit. I found my best idle results with the IAC steps in the 90-100 range.

[caver]

dunno. My 238/242 likes an idle AFR around 15:1.


Thats a pretty small cam in my neck of the woods. I generally dont bother with anything under a 264 and even those I only use on off road vehicles that need a lot of lowdown grunt.

[TAQuickness]

Thats a pretty small cam in my neck of the woods. I generally dont bother with anything under a 264 and even those I only use on off road vehicles that need a lot of lowdown grunt.


For some reason I was hearing "Now that's a knife" while I read that.

264's? any chance you are running the 8 tb manifold with these cams?

[Tordne]

Thats a pretty small cam in my neck of the woods. I generally dont bother with anything under a 264 and even those I only use on off road vehicles that need a lot of lowdown grunt.

Holly hell Batman, is that 26x at .050? That is huge!!

[ringram]

I guess there is no point closing the valve at all then? At least that way you can empty the tank faster. Whats 120deg of overlap anyway!

[joecar]

I guess there is no point closing the valve at all then? At least that way you can empty the tank faster. Whats 120deg of overlap anyway!Jet engine... pump fuel thru and light it on the way out, no ping... lol.

[johnsZ06]

Ehhh Mate...no worries! My baby 264 cam is just fer running down the road to grab some tucka! :cheers:

[caver]

264's? any chance you are running the 8 tb manifold with these cams

No knife intended.

You didnt specify at what lift your duration was measured. We normally use total duration here.
Using duration at 0.50 a 264deg cam runs around 214 deg or so.

The street cams I use on the LS1 engines run around 288 to 290 deg total.
Probably about 230deg at 0.50 lift.

[MN C5]

I dunno. My 238/242 likes an idle AFR around 15:1.

your IAC at 310 is more likely the culprit in my mind. At 310, the IAC is all the way open and can no longer add the extra air you need for idle. You may want to try adjusting the set screw or enlarging the TB blade hole just a bit. I found my best idle results with the IAC steps in the 90-100 range.


Thats pretty weird to see a good idle at AFR 15:1 interesting though. A M6? and at what RPM. You'd think it would lean pop as soon as you pushed the pedal a bit:nixweiss:

[TAQuickness]

No knife intended.

You didnt specify at what lift your duration was measured. We normally use total duration here.
Using duration at 0.50 a 264deg cam runs around 214 deg or so.

The street cams I use on the LS1 engines run around 288 to 290 deg total.
Probably about 230deg at 0.50 lift.

My spec's are at 0.050.

[TAQuickness]

Thats pretty weird to see a good idle at AFR 15:1 interesting though. A M6? and at what RPM. You'd think it would lean pop as soon as you pushed the pedal a bit:nixweiss:

m6 925 rpm. no pop's.