Hello guys, new around here.

I tried to search but found no info about this, basically my car is an evo 4 with evo 8 ECU.

My car is running open loop, and I can't make it run closed loop, the car was working perfectly fine with the Evo 4 ECU and passed the test on my country with AFRs 14.7 and 15.1 sometimes. (So I guess with the original ECU was running closed loop), now on the Short Term Trim I see 0, and mid term 0.

I know my O2 sensor voltage is moving because I did a datalog, but I can see that looks slow to refresh on evoscan.

Also I got this Cell after running the car a little bit: P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control

My Coolant temperature sensor is working.

I'm using rom 96530706 Tephramod V7



Troubleshooting:

- Disabled secondary O2 sensor, also tried with the Tephra O2 simulator but I don't see it working.

- Min coolant temp for closed loop is 37 F

- Disabled primary O2 sensor heater (since I'm running the stock Evo 4 O2 sensor)

- Scaled my injectors

- Reflashed an original ROM

- Closed loop bit is 1.

Attached is my map, definitions and datalog if you guys can take a look and help me, I'm out of options, I have another spare O2 sensor I can try on this week but since it was working fine before, with no CELs I dond't suspect of the O2 sensor.
Thank you.

 

have you logged your coolant temp? Does your coolant temp sensor have the same scaling as the evo 8 sensor? I mean you have found your problem, the ECU isn't seeing the correct temp to enter closed loop. You just need to figure out why.

I got that same code when I tried raising my min coolant temp for closed loop, so you might try just changing that back to stock and see how that goes.

 

Hi, well I didn't move the closed loop min temp, it is a stock JDM map.

I just changed some configs and now I'm logging fuel trims, I don't really know what I changed, just moved a peryphery bit I saw on a different map (bit with no name), the AFR is staying at 12.5 on my wideband, here it is the datalog.

(Oh and I reconnected the O2 sensor plug)

I notice that at AFR 12.5 my O2 voltage is 0.07808 and at 10 AFR my voltage is: 0.15616, so Evoscan at 14.7 should say 0.05 V ??? I thought that the narrowband sensor voltaje should be from 1 rich, 0.5 stoich, 0 lean.

I'm not seeing the 14.7 that I'm specting at closed loop, or I need to change something else?

Thank you!

.

 

What you should watch is the short term fuel trim (STFT) that will be reacting live from the narrowband sensor. It could be possible that your narrowband is faulty, or is not compatible with the evo 8 ecu?

 

Update! I disconnected the O2 sensor from the plug and measured the voltaje with a multimeter, I'm getting the same readings cycling between 0.0X voltajes, so I guess my O2 sensor is bad and I didn't know and I didn't have any Cels, strange.

Thank you Biggiesacks for the help, If I discover something additional I will post it.

 

That ROM has issues out of the box at least in my experience with falsely stating the P0125 code. If you search this has to do with how the rear o2 sensor was disabled.

See your ROM on the left and mine on the right where I was able to get rid of this issue. Disregard that I am using the SD version. This was the same settings I used before moving to SD.

 

So basically we need to let the rear O2 sensor enabled, but disable the heater circuit and activate the RearO2 Simulator, is this correct?

Thank you, I will be moving to SD soon

 

Yes. There are some old threads on this but you have to really read into the posts to catch it.

https://www.evolutionm.net/forums/ec...ml#post9362074

 

I discovered something weird, the O2 sensor in the evo 4 is not heated, so I have to drive my car to get the correct voltages, after that my o2 shows volts on evoscan, shows the fuel trims but the ECU is not correcting the AFR at idle, actually goes veeeery lean and bogs down when I tip in, 20:1, it does not happen at open loop, what could be?

 

At idle there will not be enough heat if the sensor cools down. Check videos on o2 sensors on youtube (I suggest scanner-danner)

 

Ok there is no way to make the closed loop to work, my STFT always stay the same no matter what the O2 sensor says:
FuelTrim_Low
-0.1953125
-0.1953125
-0.1953125
-0.1953125
-0.1953125
-0.1953125
-0.1953125

But my O2 sensor is working fine when heated:

O2Sensor
0.33184
0.35136
0.42944
0.60512
0.72224
0.72224
0.66368
0.60512
0.56608

 

I would try an evo 8 o2 sensor. I had the same problem I just put a 8 ecu in my evo 6 and my old sensor was reading and seemed fine but I also kept getting p0125. Ever since I swapped to the evo 8 o2 sensor the car has been perfect. I don't know if the 4-6 sensors read differently compared to the 8 sensor or if my old one was maybe fouled up but that fixed the issue for me.

 

Yep, With the OEM evo 4 ECU works fine, but it seems that the reading is different from one sensor to another.

I will order a new O2 sensor and will let you guys know on this thread for sure.

Thank you for the information.

 

Update!

Now is working fine.

Resolution:

Replaced the O2 sensor for an Evo 8 OEM one, Instaled a relay switch to the O2 heater, Disabled the secondary O2 sensor inside peryphery bits. now is woking fine, fuel trims working fine now.

Hope this helps evo 4 guys

 

so you set rear o2 to 0? what about o2 simulator? whats your min temp for closed loop?