Well, I've had a studder with my cam in the new 383 I built....its a pretty hot combo and I couldn't get the studder gone and once I did, it would do it at another rpm. So, I decide to try open loop....got the idle A/F ratio close and just carefully watching the A/F ratio...made two VE adjustments and went for a drive.....the studder is gone.....wooohoooo. If feels so good to not have that anymore....so much more enjoyable to drive. So, any open loop tips are welcome. Right now, just trying to get the VE correct and basically take out some tip in as well. Thanks!

 

You can probably go back to open loop once the VE tables are tuned in open loop. I usually do the following:
Tune the VE and spark using closed loop and BLMs
Once it is close, go to open loop and tune fuel & spark with a WBO2
Then go back to closed loop and tune the O2 constants and PID correction tables to match the open loop engine characteristics.

I like closed loop because it will adjust for different types of fuel and the car will run more consistent. Open loop is OK but you can get it to run better with closed loop enabled.

 

The thing is...I could never get it....it would go from 13:1 to 18:1 for no reason just sitting at idle. In open loop, its a nice steady 14.5....and everything is out. I know I'll need two different tunes and that's fine. I already have the LM-1 and I'll get the guage so I can always keep track of it. If everything is better then that's fine with me. I'm going to try closed loop again in the end but I doubt it'll be better.

 

I have experienced the same thing.........O2 drifting lean at idle. I would only run open loop before because of that and not getting the AFR above 60KPA and under 30 KPA right. What I found that worked best was to tune the VE tables to the AFR I wanted using open loop. Then switch back to closed loop and tune the O2 and PID values to what I had in open loop. It isn't easy and takes a fair amount of time.

Take a look at the O2 value using the ALDL at idle. I bet the O2 sensor is cooling off and going static (not switching). It will usually drift to reporting lean before it goes static so the BLMs are thrown off.

 

I'll take a look at it...the wideband was reporting those figures I posted up.

 

The NBO2 can only be fudged in a limited amount. Please don't expect to tune it way off stoich. +/-.5 AFR is doable, but much more will give inconsistent results. A NBO2 that cools off will never give any consistent results.

 

I've gotten everything within 13.5 to 14.5 all the time now at part throttle and cruise. Idle is about 14.2. It runs so much better in open loop. I'm going to try and use closed loop this afternoon after two more tunes I'll try closed loop again...but I expect the same thing to happen....the studder will come back.

 

I have been running open loop for over a year now with no issues. The car runs strong and with a wide band I am running 14.5 to 15.0 light loads. If you have a wideband and happy with the tune I really see no reason to go back to closed loop.

 

The more I get it fine tuned, the more I realize how different it can get...if the IAC is stuck open, MAT sensor is hot, etc.

But tuning is coming along...I'm realizing that you really need to tune the engine and a wideband is really a must. It really takes a lot of fine tuning once you get it to around 13.5:1 to 14:1.

 

So very true....

 

what about adjusting the proportional gains/ O2 sensor stuff in the bin?

 

I have a heated o2 as well so its not cooling off.

 

It sounds like you are getting the VE and spark close. That makes a huge difference in an engine working properly in closed loop. Give CL a try when you have open loop tuned. If you don't like it then go back to open loop. It sounds like CL will work for you in the end.

 

Yep...checked the plugs...looked like a little detonation was on it so I decreased timing a degree and runs smoother at part throttle now. I also fine tuned the VE a little more, its between 13.8 and 14.3 now.