whats the differance open or closed loop
TECH Apprentice
Joined: Mar 2006
Posts: 326
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Originally Posted by ty97z
what is open and closed loop?
In closed loop, the pcm controls fuel delivery according to the Oxygen sensor voltage. In open loop, the computer blocks O2 voltage readings and fuel delivery is based on TPS, MAF, and other various parimeter sensor readings. After normal operating temp, your computer should go to closed loop. OBD1 is a little diffrent than OBDII. OBDII has seven loops..if I'm not mistaken...open,closed, and five subs. @ WOT ODBII switches to the other modes, while OBD1 reverses back to open loop. I hope I cleared some things up..don't know if someone else wants to comment on this. Hey RioDeal, see you Sat.
TECH Fanatic
Joined: Jan 2005
Posts: 1,162
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From: St. Augustine, FL
I know a guy that says he isn't running O2's at all and that it simply keeps his car in open loop all the time... is that true/possible? I'm not very knowledgable tuning wise and was wondering if there is some sort of benifit running this way? I'm assuming the gas milage would be shitty and it wouldn't be very good unless the car was tuned good.
This same guy dynoed at 313hp/357tq with CAI & header back exhaust, and new valves with a 3 angle valve job. This is all he claims to have done and he's not a bragging or sneaky type of guy so I want to believe him but that seems high for an older LT1 with over 100k on the clock.
So what are the benifits of running open loop all the time if any and what are the problems with that as well?
This same guy dynoed at 313hp/357tq with CAI & header back exhaust, and new valves with a 3 angle valve job. This is all he claims to have done and he's not a bragging or sneaky type of guy so I want to believe him but that seems high for an older LT1 with over 100k on the clock.
So what are the benifits of running open loop all the time if any and what are the problems with that as well?
Teching In
Joined: Jul 2005
Posts: 21
Likes: 0
From: Ohio
In open loop the car isn't accepting information from the O2 sensors until they reach I think 600+ degrees. And the coolant has reached its minimum temp around 140 degrees. In closed loop the PCM starts accepting date from the 02's and making short term fuel corrections to try and hit the target stored Air/fuel value which is 14.7:1 in the stock PCM. It will slightly bounce above and over to reach that target. If the short term corrections can't do so it starts learning for long term corrections and stores them in things called "cells" until it reaches that 14.7:1.
At WOT the O2's are again ignored but the engine switches to a much richer A/F ratio 11.7:1 if its factory tuned.
The downside of running open loop all the time is poor gas mileage, and most importantly running into the risk of having an extreme lean/rich condition and the pcm will have no way of adjusting to it. Which can be catastophic to the motor.
At WOT the O2's are again ignored but the engine switches to a much richer A/F ratio 11.7:1 if its factory tuned.
The downside of running open loop all the time is poor gas mileage, and most importantly running into the risk of having an extreme lean/rich condition and the pcm will have no way of adjusting to it. Which can be catastophic to the motor.
