Closed Loop Operation Questions

[Kevin Doe]

Ok guys, I've got my VE table honed in within 0.5%, and I'm sitting at 0.995% BEN all across the entire map. I spent a ton of time getting this right. I'm getting about 18 mpg (in a 2900 lb car) which isn't great from what I expected. I have been running in open loop speed density the entire time. I have a few questions.

1. What are my options for running closed loop in speed density? I'm thinking that I can still run closed loop fueling in speed density, correct me if I'm wrong.

2. When I return to closed loop, I konw I need to monitor trims. From my understanding the short term trim is basically a trim based upon 02 readings directly. The long term trim is learned from the trends in the short term trims. Eventually the short term trims will minimize as the long term trim steadys out. Again, correct me if I'm wrong. Now the question. Is the long term trim I'll be logging a single value, or is there a map of long term trims and I'll just be logging the trim from the particular part of the map that I'm operating in?

3. From some research it looks like the long term fuel trim is added to open loop operation, but if and only if the trim is positive (adding fuel). Correct me if I'm wrong.

4. I know I should be logging trims. Are there trims for each bank, like a short term for each bank, and a long term for each bank? What are their parameter names for an LS1? What other parameters should I pay attention to when I make the switch back to closed loop speed density.

5. Will this really be beneficial if my VE map is within 0.5% in the majority of cells?

Thanks in advance for the help and direction.

[joecar]

Kevin,

1. Yes you can run CLSD (LTFT trimming). If running a COS, you could run semi open loop (STFT trimming).

2. Yes, your description is correct... when STFT's reach a threshold, they get zeroed and the LTFT's get adjusted. There is a 4x4 map of LTFT's for each bank, from scantool go Calibration->Long Term Fuel Trim Cells.

3. Positive LTFT's get added to OL fueling (richer of B3605/B3647 and B3618) only at WOT (the PCM goes to OL during WOT).

4. Yes, each bank has long and short fuel trims... look in the pid list under the PIDs tab, you'll see them... LONGFTn and SHRTFTn where n is 1 or 2.

5. Yes it is, it means your VE table closely reflects the actual cylinder airmass... this matters if you want to dial in your AFR's using the what-you-set-is-what-you-get method.

Joe

[Kevin Doe]

If I understand what you're saying, when running closed loop speed density (CLSD) with the stock OS I can only run with the long term fuel trims active? The short term trims arent' active? They only update the long term trim which is active?

[joecar]

In CL, both STFT's and LTFT's are active... but the way it works is when the STFT's get big enough the PCM zeros them and bumps the LTFT's...

STFT's are very transient, LTFT's are more steady.

BThere is a parameter to trim using only STFT's in the stock OS, but I haven't played with it yet; see B4206.

In the COS, there is a way of trimming using only STFT's (semi open loop).

[Kevin Doe]

I'm glad I misunderstood. I was thinking taht would be pretty messed up if that was the case.

[TAQuickness]

18mpg does seem a bit off for the vehicle weight. I'm at a porky 3700 with a fat mix (13.8 @ cruise) on a lumpy cam (238/242 115) and get 22 on the hiway if I keep my foot out of it. On average I'm seeing 18 city/hiway with a few spirited sprints.

You may want to have a look at your DFCO settings for improved economy. I had to bump my enablers way up so it would activate with my cam. I further tweaked the settings to come on faster and ramp out smoother.

All and all, with DFCO tweaking I picked up about 3 mpg and greatly improved the engine braking capabilities.

[Kevin Doe]

Yeah, my 18 mph was a mix of driving. Some highway, some stop and go, and a day of autoX. I expected to be in the mid 20s, and maybe hit 30 on the highway (70 mph puts me at 1800 rpms).

I have the stock GTO DFCO settings. I can tell that it turns on during decel, but I may be able to tweak the settings so that its in effect more often.

Can you elaborate on the settings you changed? Maybe some screen shots. Or I'll post up my tune and you coudl modify it and post it back up? Maybe post your tune so I can check our your DFCO settings?

[TAQuickness]

Send me a PM with your email address and I'll send you a copy of my current tune.

I used the RR to dial the DFCO to my liking as well as resolve the "school-zone" bucking (from your other thread). In both cases, the changes required to satisfy my SOTPD were so minor I don't think I would have ever been able to nail it w/o the RR.

[Kevin Doe]

SOTPD? Sending PM now. Thanks.

[TAQuickness]

Seat Of The Pants Dyno