Headers/Cam O2 swtichpoint tuning for stable cam idle???

[brandon6.0]

Hey I have been tuning for a few yrs and have a pretty decent understanding of it. What has had me troubled for a while now, is tuning the o2s for a stable cam idle with longtubes etc. A recent car I tuned/swapped was a 74 caprice that we installed a gen4 5.3 with a smallish 112 cam. Car had all the basic bolt ons headers, dual exhaust, cai etc. Cam sounded great, just loped all over the place.

When I had the tune pretty much dialed in with a 3-4% fuel trims and 12ish AFR, I figured we were done. Until it came down to get the nice lopey cammed idle. I had idle dialed in nicely besides the usual o2 switching and unstable idle. Car would idle fine around 14.7 afr (verified with a AEM wideband) thin jump 16ish to 17 afr. When this happened, car would lope hard with the lean idle thin o2s pushed fueling back to 14.7 and lope would change up and vis versa. Ive always had a hard time getting the idle just right. I usually force idle into open loop, which works ok and keeps it more stable since narrow bands aren't pushing it around.

What is the trick to keeping the idle around the 14.7 afr (or being controllable). Also I would like to be able to get a cammed car to have that nice smooth idel chop. Not like most cars that lope steady and smooth one minute and thin fueling changes and the lope changes. Whats the secret?

Ive read a few threads on this and kinda have an idea of what to try on the next car. I know GHuggins had a few good ideas as well. Hopefully he chimes in. Thanks in advance.

[1364838952]

Everything I read says in order to get good idle qualities you have to work in;
1. IN PARK and IN GEAR idle spark advance tables
2. RAF (base air flow)
3. VE Table

Not in that order, or maybe in that order... I've also read that on larger cams that you sometimes need to let them run a little leaner at idle due to reversion, over-lap, and unburned gas making it to the O2 sensors. I'm a NOOB so take it, or leave it.

This video; https://www.youtube.com/watch?v=o_2g...4Igjgtfb4TxnTR
kind of oversimplifies it. But the technique will get you to a point where the engine will run and then you can make necessary changes from there. RUSS K has a GREAT Idle configuration set up that you can find, and download from the net for free. I found the series of videos I linked above very intuitive.

I'm envious that you have been doing it for a few years. I'm just getting started.

[brandon6.0]

I understand all the timing, raf, and ve/maf part of tuning. No issues there.

The main thing im concerned with, is when u have longtubes or cammed the o2 mess with fueling. I also understand needing a leaner idle, which makes a cammed car sound better anyways. But when in closed loop the o2 are pushing the fueling back toward 14.7

I can watch the wideband and afr will read 16ish and car will sound awesome, thin fueling jumps to 14.7 which changes up the idle. It basicly bounces back and worth between the 2 afr's. I can even try pushing fuel trims toward the 14.7 but car will still go toward leaner afr. Its like a back and forth thing.

On a sd tune i dont see this as much. Idle seems for stable. This mainly happens on maf only tuned cars. The maf fueling swings between a few diff hz columns and makes idle unstable as well. So i dont know. Still waiting on a decent reply on this.

[1364838952]

Brandon, I know there was some discussion about changing injector timing when long tubes are used to account for the placement of the O2 sensor in the long tubes being different (further away from the engine).

I think I understand what you are asking about though. You are saying you can't get the car to stay at a consistent AFR regardless of what you do in the tables due to the PCM pushing the mixture lean/rich/lean/rich/lean/rich as it constantly tries to maintain a specific AFR that you have tuned into it. I've been seeing a lot of people saying that they go to an "open loop" idle scenario to fix/correct exactly what you are talking about. Only when under power, off idle, do you go into closed loop. post #10 in this thread; https://forum.hptuners.com/showthrea...2002-Camaro-OS might have the information you are looking for.

If it helps, please post back and let us know what you did so that anyone else searching this subject can find your solution.

[brandon6.0]

Tht definately helped alot. Thanks for tht.

How do u figure which airflow mode your in for a certain switch point?

[anniversaryss]

I've read on here that for long tubes you would want to increase your integrator delay to adjust for long tubes also .

[brandon6.0]

Ok ill give tht a try as well