93turbo5oh

closed loop is stoichometric. WOT it goes open because it fattens it up to about 13:1. i dont care what those tables say. it goes open unless youve made it so it doesnt. and if thats the case, its lean as hell if you set if for closed at WOT.

97Z-M6

wrong that is what its trying to do. and if everything is right it will be stoichometric. who told you that it is open loop at wot. becuase they dont know what there talking about.

what makes you say that if you go wide open and target 13.0to 1 that its open loop. what data do you have to show the car is in open loop at wot. you said you dont care the tables and scanner says, well what can you show to prove me wrong.

can you send me a datamaster file of your car making a wot run. and allso freescan does not show open loop at wot. you can lock the short terms blms at 128 and the car will still show closed loop at wot.

also if you program the car to stay in open loop it will not use the pe tables it will try and target the open loop a/f ratio vs map vs temp table.

prove me wrong. because i can send you files that back me up.

im not trying to argue

93turbo5oh

what are you considering closed loop?

i have factory diagnostic manuals for techs.

based on that, the 02s are narrow band. meaning they only read stoichometric. so they cycle around 14.7:1 to keep the catalitic converters alive. if it is closed loop and the a/f isnt cycling around 14.7:1 the pcm will set a code because something is wrong.

when the 02s arent being read by the pcm is called open loop. this occurs before the engine has come up to operating temprature, before the 02s have come up to temprature, at WOT and sometimes in highway cruise the pcm will go open so that it can go leaner then 14.7 to conserve fuel.

as far as 13:1, thats why my car runs at WOT. i have seen it anywhere from 12.2:1 to as lean as 13.4:1. generally, on NA setups the factory shoots for 13.0:1 based on their calculations because thats the 'sweet spot' for power and reliability NA just like 12.0:1 is the sweet spot for a power adder car. the differences in what the a/f actually reads and the desired a/f can be affected by things such as fuel octane, how good the fuel pump and filter are flowing, what timing table the pcm pulls for a certain load value and so on and so forth.

its not possible for the pcm to shoot for anything but stoichometric in closed loop because that is all that narrow band 02s can read. im not saying its not possible for it to be richer or leaner based upon wideband readings, but all the pcm knowns is rich/lean. thats how it cycles. anything fatter then 14.7 the pcm reduces pulse width and anything leaner the computer increases pulse width to the target a/f, stoichometric 14.7:1. its all about emissions. thats why i said i dont care what your files say.

in closed loop, the pcm will pull out pulse to get the desired a/f until the 02s read the desired a/f even if pulse is increased. and vise versa if the car is running leaner then the target closed loop a/f of 14.7:1. for instance a fuel pump. these obd2 pcms hold closed loop longer after going WOT for emissions reasons, but they do go to open loop under WOT if put there for more then a few seconds. its a real pain in the *** to tune a forced induction setup with this setup because the pcm tries to hold it dead lean and you have to tune around it or end up with blown head gaskets or melted pistons.

93turbo5oh

here is something i found from the SEMA technical affairs dept.

97Z-M6

the key word to that whole phrase is typical meaning not all. im sorry i disagree and can prove it.

93turbo5oh

ill have to dig up my old tech school books on obd2 gm electronics from 2001. id really like to put a wideband on your car. and since obd2 is a universal system as far as diagnostics go, they are, for all intensive purposes the same across the manufacturer lines. they all run on the same prinicple unless its like a gen 7 that is closed loop on a wideband or some of the old open loop only early DFI stuff that didnt even run 02s.

97Z-M6

i dont think you understand what im saying. when you go wide open throtle the car is not in open loop. if the blms are lower than 128 the car will put the lt blms at 128 and if it has a lt blm of more than 128 the pcm will use the last lt blm and add that amount of fuel and you can see the blms stay where they were. but its not open loop. once your o2s reach 600 degrees, and the pcm times out, and the cooant temp reaches 140 degrees, you will go closed loop and the car will never see open loop again. until you kill it and crank it back up.

keep in mind im obd1.

would you like to see a scan of a wot throtle run and the pcm staying in closed loop.

Injuneer

The problem here is "semantics".....

GM only uses the term "open loop" for the cold start condition - O2 sensors are ignored because they aren't working.

When the O2 sensors reach operating temp, coolant reaches the required minimum temp, and the timer times out, the PCM sets the flag for "closed loop enabled". The PCM now uses the feedback from the O2 sensors to alter the short term fuel corrections.

When you reach certain combinations of RPM and and TPS (it is not "WOT") - e.g. <2,800rpm/66%; 4,000rpm/38%; 5,600rpm/28% in stock programming - the PCM enters what GM defines as "power enrichment mode" (PE) (not "open loop"). The "closed loop enabled" flag is still set, and this will show simply as "closed loop" in some scan programs. Doesn't mean the PCM is still accepting feedback from the O2 sensors. Yes, it is still reading them, but the key here is in PE you get "learning disabled"..... it isn't doing anything with the readings.

In certain conditions (BLM's adding fuel) the PCM willl use the BLM's for PE mode fueling. In other cases (BLM's deducting fuel; certain EEC duty cycle condtions) the PCM will ignore the BLM's during PE mode.

97Z-M6

the pcm still will use the st for fueling in pe mode. if you set the car to go into pe mode at 0% throttle for idle purposes. it will still udjust the fuel at idle using the st and you can see it on the wide band. this where people have problems with cams thaT have alot of overlap becuas eyou can make the car stay in pe mode at idle and lock the lt blms to 128 in pe mode (at idle in this case) using the blm locker. and then crank the car and watch the wide band and you will see as soon as the car goes closed loop and it will enter pe mode becuase your idleing and you will see the st start to move and so will your fuel ratio on the wide band.

now im saying it does use the st in pe mode. but since when your runing down the track you are not in pe mode enough fro the pcm to make good use of the small numbers it gets from the o2s.

Injuneer

I get hundred of scans to review for people, and they all show the INT's at 128 in PE mode.

Let's try it this way.... what A/F ratio are the st's trying to correct to in PE mode? The target A/F ratio in PE mode is a variable, calculated from tables for coolant temp and RPM. In general, the target A/F ratio in PE mode as about 11.7:1. Since the stock narrow-band O2 sensors are not accurate at any A/F ratio more than 0.1 A/F unit from the stoichiometric value (i.e. 14.6-14.8:1), how could they use the readings to measure 11.7:1? The characteristics of the sensors cause them to exhibit larger swings in output millivolts at elevated A/F ratios due to small changes in operating temperature, than the output changes caused by major changes in A/F ratio. And, the hysterisis of the sensor compounds that accuracy problem.

97Z-M6

im not saying they can tell you your running 11.7 im saying they can tell you your runing rich it dont know if its 10:1 or 13:1 but it knows rich or lean.

my target in my car is 12.8:1. im not saying that it is something to use (the o2 readings) but all im saying is that if you program the car to stay in pe mode at idle you will see the st trims move from 128. the reason they will move is because pe mode or wot, or what ever you want to call it, but it is not open loop. it even using a closed loop cell (15).

under normal driving (or idleing for that matter) get the blms to 128 and watch the st trims you will see them jump arroud to 120 to about 130, it making corrections but the correction are not enough to set a long term change from 128, but the short term numbers are used. and since the wot or pe mode is a closed loop operation those numbers are not disreguarded. im not saying they are a value that will through your whole fuel curve off.

but the thread and this talk has been whether the wot is a closed or open loop operation. and noby has given me any data to show it a wide open loop operation.

fred take any of those scans and at wot datamaster will still show the car in closed loop and it will also show when your in pe mode. so set a tune to idle in pe mode and scan it with data master and look you can watch the st move.

in pe mode idle. if you change the maf table to 10 % less than they currently are and you can lock the LT blms at 128 with the blm locker and the st trims will go all the way up to 160 and if you put a wide band on it. and get a reading when you first crank the car ( in open loop) when it goes to closed loop you will see the st trim go up and peg out (becuase the maf changes) and the a/f ratio will change becuase its using the st trims to calculate fueling, and compinsating from the lean condition.

all im saying is that wot is a closed loop operation. all the requiremnets are met for cloosed loop operation so why would it be any other way.

bunker had this issue tunig a ( big overton cam) in a stock bottom end and when he locked the blms and program it to pe at idle. the st went high and added fuel and stared smelling rich when it went into closed loop idle (pe mode)

all im asking is to try it.


if you would like i can scan my car tomorow and send the file and the data master file as well.

rskrause

I am getting a headache. Just read what Fred wrote and absorb it, please. The O2 sensors are ignored on an LT1 when in PE mode.

Rich

97Z-M6

i respect both you and fred and what yall have to say.

but i can send you files to prove it from three differnet cars if you like,

would you agree that wot throtle takes place in closed loop not open loop.

oh and take 2 asprin every two minutes until all feeling goes away.

dmoor88

smart ***. where are you dumping your clutch to cut that 60' time vince?

97Z-M6

about 3000 . i need some more track time to get it right.

my 60s suck