does anyone one know if the data from the O2 sensors is valid under an open loop condition. I'm asking because my car under wot and open loop, the O2 sensors give a reading of around .93 volts steady +- .01 this makes me think the car is going rich. under closed loop it is switching like i think it should. thanks.
ATTN: tuners
- Thread starter adisont
- Start date
CarlisleLandOwn
Registered User
narrow band o2 sensors are not good for tuning anything other then 14.7:1. Beg, borrow, buy a wide band.
Jason Wild
Registered User
Stock 02 are not made for tuning your car get a wideband
Scott Long
Registered User
If I remember correctly the car stays in open loop until it reaches a certain coolant temp. Now some say there is a time limit and that it will go to closed loop regardless. However on my SC w/ a 160 t-stat it ran pig rich all the time since the computer stayed in closed loop all the time. I put in a 180 t-stat and it got a ton better gas mileage and had more power too due to leaning out the mixture and going into closed loop where the 02's were being monitored.
The car should only stay in closed loop until the temps reach between 160-179 or so and then over that it thinks the engine is warmed up and switches to open loop programming. If your coolant temp sensor is bad or your t-stat is too cold it can stay in closed loop and run rich and not have as much power as it could have.
The car should only stay in closed loop until the temps reach between 160-179 or so and then over that it thinks the engine is warmed up and switches to open loop programming. If your coolant temp sensor is bad or your t-stat is too cold it can stay in closed loop and run rich and not have as much power as it could have.
Scott Long said:
Just about all of this is wrong, I think most of it you just got confused and mixed up you'r words. The bottom line is narrow band 02s can only accuratly measure 14.7 A/F and thats all they need to do. You cant use them for tuning you'r car at WOT. I have seen the charts and stupid displays that people sell and i know that when i drive my car with a WB installed and watch the factory 02s with my star tester im running say 13.0 A/F and the factory 02s are pegged rich. So if i would go buy the charts i have seen my WB says 13.0 A/F the factory 02s are telling me 11.5 A/F. I guess i should lean my car out and see what happens.
It will allways go open loop at WOT. It is then running on the base fuel map with help from the MAF, temperature sensors air and water, and the map sensor for altitude. That is not to say that it isn't influenced by the o2 sensors. When in closed loop they help build the fuel map with short term information that is saved, and slowly modifies the long term fuel maps. The sampling rate of the ECU and the speed of the o2 sensor are able to derive air fuel ratios from 20 to 1 up to 10 to 1 to monitor and modify the fuel maps. The information is not as reliable, and accurate as a wide band output, and is not very usefull to someone trying to tune with a volt meter. All those cute little air fuel ratio meters that people have in the guage pods on the window pillars are not much more than pretty lights. Well anyway that is a very simplified version of what you were asking about. Later
Danny
Danny
S_Mazza
Registered User
Adison,
It sounds to me like your car is behaving right. Like Merkur said, the O2s do not really control the fuel delivery at WOT. The computer just uses the pre-set fuel map (plus any edits made through long-term trim).
And it should default to a slightly rich mixture at WOT.
Also, like BKB said, you can't tune based on the output from a narrow-band O2. You might be able to get close, but it's not worth staking your engine on. Think of it like trying to balance a pencil on its point. One micrometer to the left, and it falls way left. One micrometer to the right, and it falls way right. There's just not enough range to make an accurate tune.
It sounds to me like your car is behaving right. Like Merkur said, the O2s do not really control the fuel delivery at WOT. The computer just uses the pre-set fuel map (plus any edits made through long-term trim).
And it should default to a slightly rich mixture at WOT.
Also, like BKB said, you can't tune based on the output from a narrow-band O2. You might be able to get close, but it's not worth staking your engine on. Think of it like trying to balance a pencil on its point. One micrometer to the left, and it falls way left. One micrometer to the right, and it falls way right. There's just not enough range to make an accurate tune.
thanks, i realize that the narrow band o2 are for closed loop only and not a reliable tuning aid. i'm using an autoxray 3000 which shows the live data that the computer is recieving and noticed that my o2's were going to around .92 when at wot and open loop. i would expect some where around .75 to .80 for a wot fuel map. i would think that this would be a ballpark number for the a/f ratio. i agree a wideband would be alot better, but i don't have one at the moment. i plan on putting a 94/95 blower on the car with a 70mm tb the exhaust is do, maybe alittle small with a 2.5 midpipe but still an improvement. i don't wanna lean it out and burn a piston. i've also got a 190 lph fuel pump and i thought that might be skewing the a/f ratio at wot. thanks again for the help.
David Neibert
SCCoA Admin
adisont said:
Fuel pump doesn't matter, the regulator will maintain the same pressure if it's a 110 lph or a 255 lph. You can't use the info from the stock o2 sensors to set or check WOT A/F ratio, because they are not capable of reading the A/F ratio range you need to be in at WOT.
You are better off putting the car a a dyno with a wide band, than what your doing now.
David
i think i have misunderstood something here. in a closed loop the a/f should be? 14.7? which is what i tend to see with the scanner with a o2 reading of .25 to about .70 which is around an average of .45 which i understand is the target of the eec. and wot is based on a programmed map and the target here is ideally around 12 to 12.5
The signal from the o2 at wide open throttle is valid, but is not being used by the ECU. The fuel maps are modified over time by the information obtained by the ECU from the o2 sensors while in closed loop, and will change the WOT fuel map because it is a mathmatical calculation based on the same fuel maps that are being modified in closed loop operation. The signal you see at WOT is pretty much useless to you because it can only tell you if you are richer or leaner than 14.7 AFR. Later
Danny
Danny