Hello everyone, I've been having issues with my 03 evo 8 right after getting it tuned, and I need some input and advice.

So I recently dropped my car off at the shop a few weeks ago to get the car tuned and go speed density. Well before they were gonna tune it, my tuner noticed the front 02 sensor has been deleted. The previous owner tuned the car off the Wideband innovate ethanol/boost/afr gauge, and removing the front o2 sensor. So they went ahead and reinstalled a denso front o2 sensor and then tuned it. In that process they deactivated the innovate gauge to where it is now only just a gauge, has zero control of the car.

Well after picking up the car, I noticed that it ran weird at low speeds, coming off the line, and sometimes in cruise it would hesitate and felt rough, and then my CEL popped on. The car would die on idle if I turned AC on unless the car was warm after driving, and cold start the car would run really weird, and AFR's were all over the place all the time. Pulled the codes and it shows P0134. So I talked with the tuner, and we agreed it could be a bad front 02 out of the box. I went ahead and ordered another denso front 02 sensor and installed it. Well the car felt better after install, but still not right, and had the same characteristics. 15 miles later CEL pops on with the SAME CODE, P0134, and now I'm stumped, and frustrated.

My tuner said if the car isn't accepting aftermarket OEM replacement o2 sensors I need to run a genuine Mitsubishi front o2 sensor. That confused me, since the OEM one is a denso product. Does anyone have any idea? Ive searched the entire forum and it seems to have a lot of threads with similar issues but no definite issue, I don't know where to start to figure this out, I'm scared to spend $300 plus on a sensor that I have a feeling won't solve the issue. We performed a boost test, leak down test, and compression before tuning and everything came back perfect besides a few minor leaks they fixed, I installed brand new FIC1200cc injectors as well in this process before tune. Thanks for all the help!

 

is it a stock ecu car?

 

yes it is.

 

typical symptoms of a bad front 02, on a stock ecu car, that is tuned correctly......

they will run really rich at idle.

what your afr look like at idle?

 

edit- mostly all over the place but staying in the 15’s/16’s

 

sounds like an o2 sensor then...

the o2 sensors are really fragile.
taking them in and out will kill them alot of times.

no reason to use an oem one tho... ive jused the bosch ones for years with no issues.

 

Hi. Do you have a front o2 sensor and a wideband installed now at the same time? Why did they disconnect the gauge again? How do you monitor your car while driving ? I assume the previous owner had stock injectors because I am not aware you could log fuel trims without a front o2 sensor. The front o2 sensor is for closed loop(idle > cruise) …do you know if your tuner switched it to open loop all the time ? Does your car perform fine after cruise or WOT?

 

yes I have both, and the gauge still works as a monitor but it was a system that essentially piggy backed off the stock ecu, almost like a aftermarket ecu. I don’t know much about it, but he tuned the car off the wideband only(Previous owner), the car cruises fine and wot is pulls perfectly fine as well. I hope that makes sense, I’m still learning. It had aftermarket injectors in it before but I swapped them out. As far as open or closed loop I don’t know

 

Ok. So it sounds like the previous owner ran full time open loop. High egts will make short work of the front o2 sensor, as others have said they are in a brutal spot but surprisingly delicate.

Overly rich conditions can cause high egts. Make sure you don’t have any exhaust or boost leaks.

You don’t need a stock oem price sensor, a simple Denso $30 replacement works fine.




it could be a bad sensor or

 

Check the wiring to the sensor. It sounds like the car was rewired to accept a narrowband simulation signal from the wideband. That requires rewiring the ECU, maybe it wasn't wired back to the front 02 sensor properly.

a P0134 is "No activity Detected" That's unusual for a failed sensor, usually they give off bogus values when they go bad. Based on the history and code I'd be troubleshooting the electrical circuit for the front 02.

P.S. Your tuner doesn't need to wait for you to drive around and get a CEL to see if its working....... They could log the sensor voltage and short term fuel trim on the spot and see what's going on.

 

will do, thanks for the help. I’m gonna check that, and throw another new sensor in to see, if that fails again I’ll update.

 

Yeah my gut was they did a hack job with the wiring and you’re trying to figure it out. Good news is that the front o2 can be disabled if you don’t want to deal with the headache of tracing or splicing. Bad news is that you can’t dial in new injectors without the front o2.

Keep us posted

 

I have that feeling too, sucks. It’s just hard to find a direction to tackle this issue. I’ll let you guys know

 

Wondering if you have solved this yet? I am having a similar issue at least with my o2 sensor. Just killed my second one that was the standard Denso one. Runs alright for a little while then starts acting up and my CEL comes on.