Kind of a repost but this way you don't have to read the whole thread.

Well, just to experiment to determine whether or not the surge is fuel related or spark related I disabled closed loop today. The surge is all but GONE ...literally like 95% of it is gone, it drives almost like stock! Everything is better and I mean everything ...idles smooth and no longer has the tendency to want to stall when letting out clutch, upon upshifting it is much smoother going into the next gear, steady cruise is now nice and steady ....real steady and you can barely even tell there's a cam in it. Throttle response is just as good or better. Even though I'm running rich (.910 - .950) just the fact that it's not surging and that I'm not throttling or unthrottliing to avoid the surge probably offsets the difference in MPG. Being an M6 car it seems soooooooo much easier on the drivetrain too. It's just easier and way more pleasurable to drive ....I don't have to "plan" how to pull into my driveway to avoid bucking surge for example.

So now I know for sure it's fuel related, and damn tempted to just leave this thing in open loop. If I do, rather than spending hours upon hours trying to tune it perfectly on a wideband dyno .....I honestly think I could get away with open loop just by leaning out the MAF table a bit in the AFGS where I cruise so it's not so pig rich all the time. My VE tables are already altered considerably from stock to more appropriately match this cam....but IMO they don't get used anyway as long as the MAF is working. My cruise rpm and AFGS is very very limited anyway because I'm generally a super smooth driver and stay in a 1200-1800 rpm and 30-70 KPA range most of the time. I'm either driving it like that (mostly) ....or giving it some hell, during which time it isn't in closed loop anyway; so there's not much inbetween, or in other words ....less reason to really need to keep closed loop. **** we all know closed loop idle is ridiculously rich anyway, so there's another plus ...I wouldn't be dealing with that either!

I will re-enable closed loop anyway and try one or two more tunes with richened MAF to lock my BLM's at 108 in the AFGS areas where I cruise. If that doesn't work to hell with it, I will go to open loop and lean out the MAF some in those same AFGS areas.

Back when I had this thing wideband dyno tuned when it was a stock engine w/blower & headers ... and the tuner wound up disabling closed loop. I ran it in that configuration without any problems and had great MPG even while seeing .900+ mv's on my Scanmaster at light throttle. It didn't foul plugs or pour out black smoke either. I'm thinking ....since I know from experience that ~.900 cruise is ok to see in open loop maybe I'll just shoot for that or a tad leaner via my MAF adjustments. I won't adjust the whole table, just the AFGS areas where I cruise, then feather in neighboring AFGS gradually back to stock.

Does my logic sound reasonable or should I try my heart out at tuning it with closed loop enabled? I just fear that will take a lot more effort as far as surge reduction goes and not be worth the time spent anyway. BTW, this is not a daily driver ...so even less need for closed loop.

 

Beating surge by running open loop certainly works. What your doing as running a rich afr. Closed loop will shoot for 14.7 AFR. The intake charge is contaminated with too much exhaust due to your cam overlap. That mixture doesn't ignite or burn very well and that results in cam lope. More fuel into the contaminated charge burns better and lope and surge tend to smooth out. You would probably benefit from a WB system for OL tuning.

Steve

 

Thanks but that's exactly what I'm trying to avoid per my above post. What about my ideas concerning locking blm's at 108 in the areas where I surge to get more fuel just in that place where I need it?

 

so your going to richen it up so much that it maxes out the o2? with it maxed at 108 it might be too rich.
wonder if you could change the min blm to like 120 or so, then it wont try and pull any more fuel out after it reaches that number.

but really to do anything like this your going to need a wide band to take the guess work out of it.

 

How do you change your min blm? I haven't seen anything for this (pretty recent version of LT1-Edit) but I guess it could help ....let me clarify a little more:

Honestly, the car runs acceptably in closed loop in all areas except light light throttle cruise in gears 1-5 (cells 17 & 18), closed loop is not acceptable in that small range. Therefore I don't see much harm in simply adding to the MAF AFGS areas of surge (13-26 or so). Concerning adding too much fuel or too little ....why don't I just add fuel gradually in that area until the surge goes away? Cells 17 and 18 are the only ones I see during this super-light throttle surge ....in all other cells (say 5,7,10,11,8,etc) the closed loop operation is acceptable. Making any more sense now?

The think I don't get is why it uses cells 17 and 18 so much, 17 I can kind of see because it's during extrememly light throttle-on deceleration or total deceleration that it's used. Cell 18 though ....I don't get it, it's almost always being used during the really light throttle tip in or light throttle cruise in low gears; and there doesn't appear to be learning in cell 18 .....so my idea for the fix may not work the more I think about it . Maybe I should physically bump fuel pressure up to see if it will clear up cell 18 without setting blm's to 108 in all other cells?

 

sorry havent used lt1 edit in a long time, but im pretty sure you can in tuner cat... i'll have to look when i get home.

the only reason i can think of the tune being out of wack at that light of throttle is the lack of exhaust going past the o2, or overlap in the cam.
what are you o2 blms at when your in these cells?
my car was pretty bad about the o2s not reading right unless i was over 1/2 throttle. so i stuck with the open loop tune.
if you bump the fuel pressure up the computer will probably compisate for it and put less fuel in... that is if the blms are within the range of adjustment.

 

Well, it appears that the O2's read it as being rich because the blm's have always hovered around 108-116, usually one side is around 108 and the other side's around 116. My theory was that the O2's see a lot of extra air from the overlap but read it as say .... .900mv and then trim some fuel, when in reality that .900mv reading doesn't mean what it normally would on a stock cam (pig-rich). So instead of adding fuel to a surge condition that would benefit from extra fuel, it winds up taking some out, making the condition worse. These cammed cars really need a cruise ratio of like 13:1 instead of 14.7:1 ...but the closed loop's actually causing it to go above 14.7:1 which is even worse. Does this sound pretty much on par? The thing that gives me hope that I can stick with closed loop is that the really annoying surge is only happening in a very limited range (like 13-26 MAF-GPS and cells 17 & 18 ...mostly 18 is the really bad guy). This seems to be the opposite scenario of what happens during closed loop idle (blm's go higher and higher even though it's already idling rich).

 

yep that exactly what i've ran into with my and a few others.
computer would think it was at 14.7 and it actually was 17+

and yeah i got the most vacume at idle with mine right at 13.7

 

I'm not sure I agree with this statement. At idle and low air flow my car throws a ton of fuel at the problem. I limit my long terms and integraters to plus or minus 7. If I didn't my blms would be +16 at idle and low speed cruize. The O2 sensor reads cam overlap as lean because all it cares about is getting rid of the extra O2 in the exhaust. I've have made most of my cam surge go away by limiting the blms and playing with the timing. I also allow it to run rich in the surge areas by adding to the maf #'s.

 

Excellent information, thanks. In my case though I am not seeing what you're seeing at "low air flow" ...my blm's are always 108-116 in that low airflow area where I surge. Anyway, sounds like my idea of richening the MAF is what worked for you concerning surge. I wish this snow and rain would go away ....I'd go out and do some logging in a timely fashion ....

 

Sometimes I will see -5 on the integraters if I am 2000rpm or above with very light throttle(high vacuum). That is as low as my integraters ever get. I think the high vacuum aggravates the reversion. If all your integraters are low then why not lower your injector constant to bring them closer to 128?

If I limit the integrater to 4 or less the blm's will never change from 128. I guess the computer doesn't think it is a big enough short term to change the long term. Its kind of like being in open loop with a little room for error on those days when its really hot or really cold.

Mine is OBD2 so yours may be a little different.

 

i am having the excact same issue with surge at light throttle. the car is running rich, but i also had a mechanical problem. I'm in the process of putting the motor back together now, so i'll have to getthe datalink hooked up and get it to a dyno. i'm running a cam made by BRE for stockish heads. it's a big cam, but should be more driveable than the cc306. i was seeing 13mpg driving like a complete grandma and surge was bad at above idle condidtions, making me slip the clutch pretty good every time. and no, i can't let the car roll on the clutch alone with no gas. feels like a rodeo. I'll have to get some numbers for you guys and see if this info can help me.

 

That's in the constants table in TC. Not sure about edit.

 

Back from the dead. Was there ever a fix for this? I'm having the exact same issues. It's not unbearable to drive my car, but i'd like to get it as smooth as open loop.