Hi i recently got a 2019 KLX 250 and have been looking at modding it. so far the only thing i don't really understand is when and why you would need a O2 sensor delete and im a bit confused with the bit information i can find online. Any help would be great thanks.

 

I have a crude understanding of the O2 sensor. As far as I know most of normal riding is done under "closed loop" where the O2 sensor adjusts the air/fuel ratio for good mileage and low emissions.

At some point in a combination of throttle position and engine rpm, engine operation switches to "open loop" where the O2 sensor stops adjusting the air fuel ratio, and a preset programmed "map" stored in the ECU determines the ratio.

Even though I've modded both the exhaust and intake, I did not delete the O2 sensor because most all of my riding is done under the closed loop (partial throttle low rpm) conditions of a daily transportation vehicle.

I've experienced NO lean condition symptoms (excessive engine heat, exhaust popping, white spark plug insulator). The exhaust is black and sooty and the spark plug insulator is grey indicating totally normal operation.

 

Thank you, that GREATLY helped my understanding of the O2 sensor

 

My pleasure.

I'll be trying an experiment of adding a thermister to the air temprature sensor to make it seem the air is colder. Someone else mentioned it so I'll try. The thermistor should richen up the air fuel ratio a little bit uniformly across the whole operating range in both closed and open loop operation. I'll post the experiment and the results in this forum.

 

tooter, you're correct regarding Closed Loop and Open Loop .

FYI: altering the OAT ( outside air temp) input to the ECM will cause fueling alterations that range from slight overall richening, to total shutdown of Closed Loop functionality. The extent of tuning available by altering OAT is determined by the relative complexity of the programming within the ECM. There is always a "OAT Table" that lists sensed OAT's and the associated fueling multipliers - which gets "resolved" onto the final calculated Injector Pulse Width (IPW) before the pulse is sent to the injector. The size of this table ( the number of OAT / multiplier entries ) determines the relative coarseness or fineness of results from spoofing OAT signaling.. BUT, go too far and the ECM will think it is, say, 10 degrees outside, and shut down closed loop for a constant open loop "full choke" operation - not good..

 

That's what life is all about... finding out.

The guy who did it on his bike said he had no problems. He said he used a 2.5k ohm thermister. I could only find a 2k ohm and he said it would just richen the air fuel ratio a little less. I'm totally curious so it'll be a really fun $18 experiment. If it doesn't work out I can always remove it.

I've done a LOT of experiments over the years. This is one of them. I built the intake manifold on our Toyota.





The extra long intake runners make lots of low rpm torque for excellent gas mileage.

 

This problem could happen if tampering with the water temperature sensor, with IAT sensor if signal fall outside the usable range (-30+120) ECU set IAT at default 40°C.

O2 sensor delete mod is simply dumb ***.

 

With the O2 sensor and no other air/fuel modifications, my bike runs fine and exhibits no lean symptoms, no excessive engine heat, no deceleration popping, no white spark plug insulator. The inside of the exhaust is black and sooty like normal. This is likely because I'm riding in closed loop almost all the time.

I still haven't installed the thermistor yet because my bike gets used every day for work and has to be in service. But I can't wait to do it when I can get some free down time.

 

Hi All,
New member. I am somewhat grey and have played with a few vehicles over the years. I recently bought a KLX300 dual sport for me and a KLX230 for my kid.
What I have seen in the automotive world is people/companies hack the OEM ecm. You then can then understand the control strategies used by the OEM and modify them.
I have not seen an indication that the KLX250 FI or the KLX300 have been hacked.
What I have seen, and this does not mean it is the same for the KLX, is that the narrow band O2 sensor is calibrated for 14.7:1 AFR typically and it can only read accurately at low flows.
The closed loop strategies typically require certain conditions to become stable and provide correction. This correction takes some time and stable input. It then modifies fuel tables based on closed loop feedback the lag or time constant is typically quite large.
Without knowing the target AFR and the conditions that the KLX goes into closed loop, it is difficult to understand whether an O2 delete would be any good.
The benefit of an O2 delete would be to allow the user to dial in a better AFR in the range that the O2 sensor correction is allowed to impact. Effectively eliminating the variable of the O2 sensor and providing an input to the ecm that won't throw a trouble code or counter act fueling adjustments.
I have seen some impressive accumulation of knowledge here on this site. Good work!!!

P.S.
Got a PCFC just to ensure I can change fueling when or if I decide to start modifying.

 

Learning to fly...

I run an oversized high flow intake along with a wide open free flow exhaust without any fuel tuner at all.

My engine doesn't exhibit any lean condition symptoms. No engine overheating, no exhaust popping, a light grey spark plug insulator, and a black sooty muffler interior..

You're right...
...so far no one has hacked the KLX ECU. I contacted Yuminashi and suggested it to them as a new product idea, because they make stand alone self tuning ECU's for 125cc Honda Groms. I ran one of their ECU's over 10,000 miles in my Grom and never touched it. Even though I made lots of changes it always completely adjusted to each new operating condition after about 50 miles.