327_TPI_77_Maro

iTrader: (8)

Hi guys, I have the Holley Stealth Ram on my 327 now. Finally a matched combo! I can wind this motor well over 6000 rpms and it is still making more power. The motor pulls so fast to high rpms that the first time I drove it with the HSR, I had the motor cutting out at high rpms before I shifted, and thought something was wrong. After a quick check, I found that I was bouncing off the 6100 rpm fuel cutoff I have in the bin. Increased that to 6500 cutoff and now I can really take advantage of my heads and cam. I knew the HSR would lean out the motor at high RPMS, so I copied the 2 PE adder tables from a 1989 350 F body into my bin (the vette bin I was tweaking had almost no PE fuel added, and the F body has up to 30% at high rpms). I also decided to run in open loop only today, for the first time. The car is very responsive, but it could not maintain the target 800 rpm idle speed when I had the open loop afr % vs coolant temp at zero with the engine hot. When I increased the values to around 10% afr increase at normal hot temps, the car will now reach the target idle speed, but the exhaust smells rich (well it always does with this 60s style camshaft). Why does open loop need a 10% richer idle than closed loop to obtain a similar idle quality? My closed loop idle is perfect -- very stable, always reaches target speed. The open loop idle is not bad, but less stable, and requiring more fuel. Open loop still uses INT/BLM corrections, right? What else does closed loop do, that open loop doesn't, that would affect the idle fueling? Also, for you guys who run open loop all the time, did you leave the open loop afr % increase vs load active? It seems that I am going to be adding waay too much fuel running in open loop w/ up to 8% increase under heavy load, 10% increase across the board due to temp, and up to 30% increase in my PE table. The car is very responsive and is scary fast with this setup in open loop, but I'm not that familiar with what convention dictates I should be doing w/ open loop tuning.

2new2funny

ttt for ya

thirdgen88

The essence of closed loop operation is correction based on O2 input.. Open loop does not..

I'd do some more searches on tuning in open loop... You have a wideband O2 I presume??

Z69

Your tables are off if you CL is better than OL. Need to tune.
In OL, the BLM will add fuel, but not sub it. Not sure if this is true for all bcc's but you'd think it should be.
Very few people that run OL with a maf around here.
Might want to do another post with OL and 6E tuning.

327_TPI_77_Maro

iTrader: (8)

Thanks guys. No, I do not have a wideband. I always remember seeing people on this board saying, if you don't have a cat, run open loop. It didn't dawn on me that most of these people are running SD, which gives a lot more adjustability through MAP/VE tables to an open loop tune, whereas with MAF I can only control fueling, indirectly, through the MAF tables. I guess I'll go back to running closed loop, the idle was much happier that way and the car still ran excellent. Most, if not all, of the added responsiveness I saw yesterday running in open loop was likely due to the 20-30% PE I added, not just the fact that I was in open loop.

327_TPI_77_Maro

iTrader: (8)

Update -- I switched back to running closed loop at a 100 degree enable temp like before, and all is well -- the idle is perfectly stable and on target like I expected. It looks like I would need more tuning to be able to run open loop only. Is there any advantage power-wise to run open loop all the time? I have the HSR and the 327 has a big cam and big valve heads, so this is quite a ways from an L98. My car is perfectly happy cruising at the 14.7:1 ratio that closed loop dictates, and I can definitely get enough enrichment in accelerating and PE modes, the car runs flawlessly.

RednGold86Z

iTrader: (1)

If it ain't broke....
If it can handle closed loop idle and cruise, you are home free. No (worthwhile and consistent) advantage to running open loop there. You won't see performance gains in OL, and you'll be "safer" with it in closed loop.

dimented24x7

iTrader: (2)

It might be ato your advantage to tune the open loop, anyway. That way you will be able to run open loop at colder temps and have afrs set for something other then 14.7:1. BTW, the ecm also adds in some bias to the O2 to richen the idle via the BLMs. In open loop at cooler temps, you can change the AFRs to be a little richer then whats there already. Just remember that the AFRs must be 14.7:1 at all the areas the car will be in closed loop or itll remain in open loop. You could also try adding a little bit of MAF flow in the areas that the engine idles in.