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O2 Feedback Control and "Surging" under light throttle
Ok, let's talk about the PFC O2 Feedback Control function.
I have a Tech Edge 2.0 WB w/ display and a Datalogit in my car.
It seems like every time I try to adjust the idle INJ maps to try and lean out my idle, I end up upsetting the car and have my idle become unstable, causing me to have to do an "all data initialize" on my PFC to let it re-learn my car's idle. I recently did the all data init and my idle is pretty stable at 720 rpm's at 13.3-6 with the O2 Feedback Control "ON". The problem is that under light throttle, like when i'm creeping up toward a stop light, the car "surges" and isn't smooth. I like the O2 Feedback Control makes the car cruise at 14.5-15 AFR's or "Lean Cruise". Now, when I turn the O2 Feedback Control "OFF" the car idle is smoother but the AFR's drop to 11.2! The "surging" under light throttle goes away and the car is nice and smooth.
Is there a problem with my O2 Sensor or is this how's its supposed to be?
I have no explanation, but noticed the same. I have also tried to lean out my fuel map from n3-n8;p2-p9 without a lot of success. I have pulled 15% fuel out but my AFRs have not decreased significantly. Of course this is with the O2 switched off. I used to run with the O2 on altough I have the Techedge/O2 also. I just recently turned the O2 off to pass emissions, because of what you mention....the O2 feedback sending the AFRs too low.
Just richen up the cells in the low load areas where you are experiencing the surging. It worked for me. Now, however, I have the o2 feedback turned off. To maintain fuel mileage during cruising conditions, you will most likely have to lean out those areas of the map.
If so, there is an idle screw on the throttle body that needs adjustment, not the pfc. That's what had to be adjusted when I still had my twins.
However, given that I"m now a big single I laugh at gas milage, don't run a stock O2 sensor (only my wideband, also tech edge but the early 1.5 model) and turned off the o2 feedback. I've spent hours tuning my maps cell by cell along with accel enrichment so that I get pretty close to stoich in 5th gear highway cruising, got my idle right between 12.9 and 13.7 depending on ambient temp, but run around 13~12.5 in the N/A area when I hit it as I transition to boost.
Last edited by Beast From The East; 06-02-04 at 03:15 PM.
Most people have better luck turning the O2 feedback off and tweeking the cruise cells for thier target AFR.
The PFC doesn't control very light throttle inputs very well. Most people combat this by richening up the maps which masks this deficiency. It's a choise, do you want better fuel economy or smoother light throttle driving? I chose fuel economy and learned to live with the surge.
You idle issue is likely the TPS out of adjustment. If it's out of range the computer goes into some default mode and you can't make any other idle adjustments. Set the TPS to 1.3v and the AFR to 12.5 at idle.
would you guys please post some of your maps where you have leaned out the idle with the O2 off...my TPS voltage is within spec and I doubt whether you can lean out the maps within idle and some cruise conditions
1st to 3rd... why are you using 1.3v and where is that voltage specified?
Again, I am apologizing for my previous post. As you know it can be very aggravating when you things do not turn out the way you intended, specifically my attempts to richen up the idle with the O2 off. This is why I am somewhat skeptical as to whether it can be accomplished… but I have witnessed another FD owner with his AFRs in the 11s at idle. I don’t know if his O2 was on or off, however I believe it was most likely off.
With respect to my request for maps to demonstrate low AFRs at idle, since our cars are different it is unlikely whether this will be useful at all. I assume perhaps a datalog would illustrate low AFRs at idle. I am just uncertain as to why my attempts are not successful although they seem to change a little but not as proportional to the amount of fuel I have added.
And finally, the TPS voltage for narrow range fully closed should be 0.75-1.25v as indicated on page F-182 of the service manual.
I have been following this and now it is getting interesting.
I have my 02 feedback on. At cruse I see (on the WB) AFRs at 10.5 to 11.0. But that is what the correction value is in the map. Once I touch the throttle are even back off some (very touchy to make it try to run stoic at cruse) the AFR pings rich and goes back to 11.0 or so. (BTW, I have two 02 sensors. A WB for tuning and the stock NB for the ECU. Stock 02 has autometer AFR gauge). All my fuel corrections are set to around 12.0 in the light load lower RPM range. I get no surging. Although I have gone back and added fuel to some of those areas. I did this because I notice AFR of 15-16 as I swept through the 0-7 psi range when stomping on the throttle. The addition of fuel brought them down to a desired 13.
Not sure how you guys may fix that, but that is how my car is set up and I have no surging. Well very slightly on seldom occasions.
I will check my TPS voltage when I can.
Are you checking the voltage with the car off and the key in the on position OR with the car runnig at idle?
Summary for those interested is that some have issues with O2 feedback coming on at idle and low rpm/load situations (me as one example) and some do not. I switched mine off and tuned idle to as lean as possible for smooth idle which was ~13.2:1 with my streetport, and tuned cruise to about 16:1 AFR to keep the plugs clean and preserve mpg. Only issue I have with idle is when the car is shut off hot and the IAT sensor heat soaks it leans out the motor and idle gets a bit rough. Can add a couple % fuel and all is well but that richens up idle. Need a better IAT sensor!
My experience with a working O2 feedback is that it likes rich conditions. Lean it out too much and may get bucking. I prefer to leave it off and tune the car lean at low loads and cruise.
Can the Datalogic reset the O2 voltage to a/f tables?
I have installed ann AEM Uego and input 0-1v signal, but now getting surging. (was ok with stock sensor). Also if tables can be reset can I input the 0-5v signal?
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