What am I really Sacrificing Being an Open Loop Tune?
05-28-2008, 10:11 PM
#5
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great read redhardsupra. So in short you lose nothing besides MAYBE a slight reduction in gas mileage, if tuned correctly in OL. I run SD OL and have seen no problems. IM currently getting about 22-23 mph on the highway with my current setup (specs in sig) with 4.10 gears.
05-29-2008, 07:44 PM
#6
think about it this way: trims are a generic mechanism to make up for changes and variations that no other table or sensor allows us to. this way we can adopt to the situations that there's no way to account for, ie. cold fuel at the gas station.
unpredictable changes might be good, or bad. if the car happens to end up a bit lean this way, you might like it cuz the milage gets better. however if it goes lean on WOT, you're screwed. the inverse of it, rich at idle you will hate cuz it will idle like crap, kill O2s, and get poor milage. on WOT rich will just run weaker than it should.
to me (and apparently whoever makes control systems like the PCM) any fueling that doesn't _exactly_ follow my orders is a bad one. control is everything. however the universe being as complex as it is, we cannot account for everything, thus generic control systems are unavoidable. this is why you want CL, this way the computer always brings fueling back in line, regardless of what mother nature throws at the sensors. of course sensors go bad, and sometimes you have a genuine hardware failure, that's why the computer will throw errors if the fueling corrections are >25%.
After having said that, there's of course problems with CL itself. all control systems need to be calibrated. if the control system is calibrated to make certain corrections based on let's say injector size, and that's changed to bigger ones, now you will overcorrect, and the system that supposed to help you, now is screwing with you. good luck correcting the corrections
the most popular reason for disabling the CL is that the O2 sensors cant make sensible AFR readings with big cams. there's no fixing that, so turning off the CL control is kinda the right thing to do. the better thing to do is to disable CL control only at the range where the O2's do not operate properly, like the low RPM in case of cams with large overlap. MNR-0 has a great writeup on this exact issue on the HPT board.
so the short version: what you're possibly giving up is precision when the CL system works well but you disable it. when it's not working well, you either make it work well, or turn it off so it does not muddy up the picture.
unpredictable changes might be good, or bad. if the car happens to end up a bit lean this way, you might like it cuz the milage gets better. however if it goes lean on WOT, you're screwed. the inverse of it, rich at idle you will hate cuz it will idle like crap, kill O2s, and get poor milage. on WOT rich will just run weaker than it should.
to me (and apparently whoever makes control systems like the PCM) any fueling that doesn't _exactly_ follow my orders is a bad one. control is everything. however the universe being as complex as it is, we cannot account for everything, thus generic control systems are unavoidable. this is why you want CL, this way the computer always brings fueling back in line, regardless of what mother nature throws at the sensors. of course sensors go bad, and sometimes you have a genuine hardware failure, that's why the computer will throw errors if the fueling corrections are >25%.
After having said that, there's of course problems with CL itself. all control systems need to be calibrated. if the control system is calibrated to make certain corrections based on let's say injector size, and that's changed to bigger ones, now you will overcorrect, and the system that supposed to help you, now is screwing with you. good luck correcting the corrections
the most popular reason for disabling the CL is that the O2 sensors cant make sensible AFR readings with big cams. there's no fixing that, so turning off the CL control is kinda the right thing to do. the better thing to do is to disable CL control only at the range where the O2's do not operate properly, like the low RPM in case of cams with large overlap. MNR-0 has a great writeup on this exact issue on the HPT board.
so the short version: what you're possibly giving up is precision when the CL system works well but you disable it. when it's not working well, you either make it work well, or turn it off so it does not muddy up the picture.
05-29-2008, 08:17 PM
#7
The only thing I ever gave up is when they switch to the winter blend gas around here...that makes me have to do a retune to get the AFRs back in line. Other than that, my AFRs stay very nice and consistent...way more so than I would have ever thought. Plus I don't have to keep buying new O2 sensors all the time since my headers would kill them about every 6 months or so.