please explain open and closed loop for me...
i realized i know next to nothing about these set-ups. is there some kind of idiots guide to this or something? LOL
*edit* oops, forgot to add for a 95 with obdX
Edited 1 time(s). Last edited Tuesday, November 09, 2010 5:00 PM
Underdog Racing
Closed loop means a previous state affects the out output of the next state. For instance, a PID controller for commanding an AFR will use the previous AFR to make slight adjustments to the IDC so that over time, the AFR converges to that value. An open loop doesn't use feedback to control a future event. This would be an example of PE, where only current sensor values affect the AFR.
I have no signiture
In short,
Closed loop uses the output as one of the inputs to a system. Open loop doesn't.
I have no signiture
In tuning our cars closed loop is where the car tries to run based on the narrow band o2 and command a 14.7 afr. Open loop is PE mode when ever we accelerate hard or floor it. It reads from the VE tables to give the engine fuel and whatever command AFR you tune for. Thats why closed loop is turned off during tuning.
Yes, like Whalesac said -
Closed loop takes feed back from a primary O2 sensor and fairly rapidly adjusts (trims) fuel to meet a target mV reading. The immediate trims (short term fuel trims) are stored as they are repeated and a constant change is made (long term fuel trim). So the STFT is the pcm saying "what change to i need to make right now" and the LTFT is the computer saying "gee, i've needed to make this change a hundred times at this load/rpm before, so i'm going to correct it right off the bat"
Open loop means the primary O2 sensor is "out of the loop" - it is not used to correct fueling. There are look up tables (VE tables/Maf calibrations,ect depending on the specific vehicle) that determine fuel. Typically, open loop operation is richer than stoich, such as in PE mode or catalyst warm up, or very lean, such as deceleration. On all but the most modern cars, this means that the desired condition is WAY outside the ability of the primary O2 sensor's ability to compensate anyways.
ok so would a malfunctioning IAT sensor or an unplugged IAT sensor make it run in open all the time?
Underdog Racing
there's no visible modifiers in regards to IAT and enabling closed loop, only the ECT sensor.
2001 Olds Alero (LD9)
650 whp / 543 ft-lb
@turboalero
on OBD1? or whatever the hell a 95 has....
Underdog Racing
96 ODB2 became standard across the board, some cars had it prior... part of the ODB standardization is all OBD2 cars have the same diagnostic port and it has to be within reach of the drivers seat. If you have the DLC (data link connector) like everything else its ODB2. Thats one of the tell tale signs of OBD2. Although I don't know what GM used for DLC's on OBD1 cars.
Remember some 95 autos are OBD1.5..... It is a bastard child. Most 95, 5 speeds, are ODB1.
PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO
ok well i guess i dont care if someone cries im asking about my beretta LOL...
anyways, im asking for my 95 beretta. its a 3100 auto. so, OBD 1.5?
ryan- its got the port under the dash but its not the same type of plug in like my 97 and 98 cav's have...
i thought by unplugging the IAT it would stay in open loop, but it still is causing me problems when it runs in closed loop. what i need is a way to ditch closed loop so i can see if something to do with that system is causing me problems with stalling/bogging. if you are interested in more, check out my thread about it in other cars.
Edited 1 time(s). Last edited Wednesday, November 10, 2010 3:07 PM
Underdog Racing
If the port is different it's not OBD2. Another easy way to check is if you don't have pre and post cat 02 sensors you don't have ODB2.
ill crawl under it tomorrow and look.
Underdog Racing
I would like to point out that some of the 97 cavys had 1 o2 sensor and were OBDII.
That doesn't sound right, OBD-II has to moniter cat efficiency, which means a pre cat sensor to relay rich/lean info and and after cat to monitor cat effeciency.
Screaming for Mercy!! wrote:Disconnect the O2 sensor.
or disconnect the ect, which ever ones easier to get to.
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Darkstars wrote:That doesn't sound right, OBD-II has to moniter cat efficiency, which means a pre cat sensor to relay rich/lean info and and after cat to monitor cat effeciency.
i know it doesnt but pauls car is a 97 and lacks the 2nd 02. no wiring, nothing. car came from mexico.
Underdog Racing
k so i tried unhooking the temp sensor, car barely starts and runs like total ass unless its warm. problem still remains anyway so it didnt do jack.
If it takes forever.... I will die trying. Underdog Racing
