So I have an Evo 8 running an FP green and stocking injectors at 20 psi at the moment. The car was running good on a somewhat tuned tephra mod 7 ROM. It was idleing fine and cold start was good etc for MONTHS and I get in it today and when it was cold it wanted to be all the way leaned out unless it was almost in boost and the air fuel would read about right. Then when it warms up it goes waaaay rich and runs that way the whole time part throttle but then you give it some gas and get it near boost and it will lean out a bit to normal levels. Wtf is this trickery?

 

Is it SD? If so does it have the IAT hooked up? Are any of the background Fuel vs coolant temps maps altered? I am presuming not quite.

 

is your tune still in closed loop when the AFR evens out?

 

I am not on sd

How would I know if it is in closed loop? This just happened. But I did have the panel loose on the passenger side floor board.

 

it would be up to the tuner, actually. if you don't already know: there are LOAD and TPS parameters that must be met to go from open to closed loop.. sometimes tuners set them different. if it is switching over into open loop (where your tune "kicks in") and AFR is going back to where it is supposed to be, then maybe you have a bad sensor causing the car to run poorly in closed loop.

i had an issue once like this, on another car, when the coolant temp sensor went bad. just tossing ideas out.

 

My tune wouldn't be messed with closed loop or open loop. That was left alone from tephra but it has always been on this tune. When I say months its been like on this tune half a year. Maybe my mafs going bad? I tightened all my clamps so I don't think boost leak. The temp on the gauge reads perfectly like it should. I'm using a **** ton of gas just driving home now. Like 10.1 Afr at part throttle and vacuum of -7 to -8 but if I get vacuum up to .02 or in boost the Afr reads like 12 to 13.

 

i'd guess def a sensor then, yep. since it's so sensitive to airflow, MAF is a possibility. i've tested a few according to the shop manual and never get the readings they say i should LOL. do you have one you can borrow?

 

Just looked up open and closed loop. Wouldn't it be more likely then, since I still idle okay and get good Afr readings during boost that my front o2 sensor has gone bad? Correct me if I'm wrong.

 

Force it into full-time open loop by playing with the TPS and Load thresholds. Depending on whether this resolves your problem will help in determining what the problem is.

 

depends.
idle is closed loop and your boost may be open loop, depending on on where your tune's threshold is. can you do a log to see where the LOAD and TPS are when all of this changes? if you are not meeting the LOAD/TPS criteria for the tune to kick in, you will still be in closed loop. if so, then a bad o2 sensor would make the car run poorly the whole time.

i'm assuming you are in closed loop the whole time, which is why i'd suspect a sensor. plus, it was fine and then went bad all of a sudden with no changes. now.. to figure out which one.
then again, i'm distracted here at work and may be missing something completely simple LOL

 

The car isn't meeting open loop until I put my foot down to get the load values to bring the Afr back to around 12 or 13 I'm assuming. On cold start the car runs lean as **** in closed loop and rich as hell in closed loop when warmed up. That's the vibe I'm getting from my studies. Since I found out what closed and open loop was I've figured out my issues are simply in closed loop (off 02) unless I have them backwards. Yes just started out of nowhere as well so I can only assume something stupid has happened. The o2 is like two years old but that doesn't mean anything. I'll buy aanother anyways and I will keep everyone updated. This sensor is the one that made the most sense to me so far due to symptoms. Lean until warmup then rich after warm up. I'm reading things about o2s and that they work differently cool to warm. Correct me if I'm wrong.

 

okay, i think i get what you are saying a bit better now. when the car is cold, you are in open loop and the o2 sensor is not working. the car is only using a few sensors such as coolant temp and MAF. i can't remember which all are in use. the car is running a pre-programmed map based on these sensors. there is no reason for it to be the o2, unless i'm missing something.

the key is figuring out which sensors are used in both closed and open loop since you are having issues in either. your problem should be one of those.

again, i'm distracted at work so i may be missing something super simple that someone will probably chime in with any minute LOL

 

My understanding was like this: in closed loop you run off of the mat and the front o2 sensor. In open loop you run off of the maps in the ecu. Since you start up in closed loop with the o2 working and then you drive around part throttle the whole time in closed loop I am assuming the o2 is my issue. The open loop only comes in when you reach a treshhold in the preset determiners programmed into the ROM. So when I am cruising around my Afr is crazy off (closed loop) but when I get in boost it seems to do much better (open loop).

 

Not quite. When you start up the car, you are in open loop until it warms up. You are not using the O2 sensor. Since you are having issues in both open and closed loop, it's most likely not the O2 sensor giving you problems.
You most likely have an issue with a sensor that is involved in both.
Why it goes normal under boost is odd.

 

Closed loop uses the o2 sensor.