pHEnomIC

iTrader: (14)

I would like to finish tuning my car so I don't have to lug around the laptop anymore. At this point my car runs very good. No drivability problems, idle is good, etc. I did wideband ve corrections and have a very nice smooth ve table. Additionally, my maf is corrected and i get very low a/f error against my maf table. WOT is under 3% error at any given time and usualy under 1%.

My problem, i decided to enable closed loop to help some surging as i heard it would help as well as save on gas(heard it does this). So i enabled it and reset my fuel trims. Drove around a few days and most of my ltfts in the part throttle areas range from 8-10. I am wondering what should I do? I do not want to start from scratch again. Can I just add the ltfts to my ve table and smooth it out again?

Silverhawk_02TA

Enabling closed loop will jack your fuel trims if you've tuned it in open loop with a wideband. Sticking narrowband O2's at the end of longtubes will throw their perceived AFR significantly out of whack, which is what you're seeing. The O2's are reading leaner so the PCM is compensating.

Closed loop operation typically makes surge harder to tune out. It also won't save you any gas. In open loop you can command any AFR you want in any cell you want, making it easy to maximize your tune for best gas mileage.

In other words, you can achieve your goals in open loop more effectively than in closed loop. I'd say leave it in open loop and optimize your tune.

pHEnomIC

iTrader: (14)

So you think that my tune is probably fine and i should just go back to the open loop?

What would be a good strategy for increasing mileage a bit. It seemed to get 11-13 consistently in open loop city that is and just this past tank in closed loop i got 15. Could be different driving but anything else i can do?

Im thinking that my cam's low lsa, 111, is confusing the nb's as well.

Silverhawk_02TA

Yeah, LT's plus overlap equals unhappy O2's. You can run successfully in closed loop, but it's far from optimal.

As far as increasing gas mileage in open loop: What AFR are you commanding currently? Keep in mind that the PCM is calibrated to use the stoichiometric AFR (14.7:1) because it has the least emissions, not because it nets you the most power or best gas mileage. You can lean out the AFR in the cruise cells quite a bit, and Holden vehicles even do this stock with Lean Cruise mode. This isn't enabled on our PCMs because of federal emissions regulations, but you can achieve the same effect by just commanding a leaner AFR in the cruise cells in open loop. Just be careful to adjust your spark tables accordingly and log to make sure you aren't getting any KR.

pHEnomIC

iTrader: (14)

I am commanding 14.7 at cruise and i believe 12.5 or something through pe at WOT.

What would be a good safe number to command for the cruising/part throttle cells? Can i go a lot leaner or just some tenths?

Silverhawk_02TA

It's going to depend on your individual setup, but I think a realistic goal would be somewhere around 16:1, plus or minus, again depending on setup.

It's just going to take some more logging and tweaking to find the best AFR and spark combinations for those cells for your setup.

pHEnomIC

iTrader: (14)

My wideband is simulating nb on one of it's outputs so maybe that could be a factor in this. I got the voltages set correctly and the refresh rate lowered.

Anyhow, I logged wb a/f today in closed loop. Part throttle and cruising seemed to be ok. 14.7 was commanded and actual ratios didn't stray too much. At wot though, i am commanding 12.5 through p/e. But actual is ~11.8 consisistently. So the ltft's are definately carrying over. Looks like im gonna have to do a calibration and check again and if i still have problems, i will go back to OL MAF.