O2 Sensor Simulator

[jakejm79]

So replacing the front o2 sensor seems to have fixed the problem, correct outputs from both the front and rear (simulated). Now just to put some drive cycles on the car and see if it passes catalyst efficiency. Ended up using the one I made myself since I pretty much destroyed the one I bought.
Front:


Rear:


Homemade o2 sensor simulator:

[jakejm79]

Success

[BobSaabit]

Jake:

What do you use to take these reading and chart the waves?

[jakejm79]

Torque for Android (on my phone) paired with a cheap ebay BT OBDII reader.

[jakejm79]

So I think I spoke too soon, I now have a CEL for lean condition, long term fuel trim. I'm pretty sure its related to one of the following since it appeared (and has done twice after resetting) right after replacing the front o2 sensor and connecting everything up:
1. My new front o2 sensor is defective (I do notice extreme lean conditions when coasting at higher speed (i.e. high vacuum levels)).
2. The simulator is causing problems (see more on this below).
3. I have an underlying issue that was being masked by the malfunctioning original front o2 sensor.

I have disconnected the simulator for time being to see if my lean condition comes back. My STFT seem to fluctuate between 5-10%, is this normal (LTFT seems to show 0% I'm not sure if its something that can be measured by torque).

I did find this in the WIS with regards to the rear o2 sensor:

To improve exhaust emissions still further, the value from the sensor is used to correct the closed loop. The most favourable emission values
are obtained when the oxygen sensor voltage is 0.6 V.
If sensor voltage is 0.3 V, for instance, the engine is running on a slightly lean mixture. The closed loop will then be corrected so that the fuel-
air mixture is kept rich for a longer time than it is kept lean, thus increasing the sensor voltage.

Does this mean that the rear o2 sensor does have an effect on mixture, just in limited way?

[BobSaabit]

Originally Posted by jakejm79

Does this mean that the rear o2 sensor does have an effect on mixture, just in limited way?

I don't see that it can be read any other way, as long as it is actually referring to the rear sensor. The WIS can play a little loose with languge sometimes so triple check that.

It does violate conventional wisdom that the rear is only there to check the cat efficiency.

[jakejm79]

I agree Bob, it is clearly under the rear sensor:


I think the idea is meant to be if you have a front sensor that starts to go bad, reading leaner or richer than it should, it is double checked by the rear sensor and if there is a difference then the ECU will compensate, so while the rear sensor doesn't directly control the mixture it will have an effect on whether the car runs rich or lean.

I'm not sure how great an engineering idea this was, the rear is used to compensate for a less than optimum front sensor, if the rear sensor is the problem then it could lead to in accurate mixture especially if the front sensor is fine.

Now whether my problem is caused by the simulator tricking the ECU into thinking it is running too lean when the new front sensor is working flawlessly or if the new sensor was bad out of the box I don't know.

[Payne4life]

for the post cat O2 sensor, you can use the spark plug non-fouler trick.

stole this from s10forum.com
Re: Do it yourself o2 simulator

It works, and there is no need to cut any wires or anything...very easy as well.
I personally have driven about 300 miles since, no CEL. So anybody who wants to run a test pipe...here is the mod you should do to stop the CEL...don't bother with the electronic ones with only some of them working...and not working all the time. These pics are from it being done STi, but I did it on my S, works just the same.





or


Those are the Spark plug, Anti-Foulers you'll need to do this..just pick them up at any auto parts store

[jakejm79]

I've heard of this not always working (it seems to work better when you have a race cat rather than no cat, you can see in the pictures that there is actually a cat).
Also it can take upwards of the 300 miles for all the tests to complete, a CEL wont be triggered while the test is still incomplete.

[Payne4life]

he has a gutted cat. its one of the fake ones you can buy if you need it to pass visual test. ive seen the original post of this sti but forgot where it was but hes done a lot of miles and still no light. its only a few dollars and a whole lot cheaper than having it tuned out or getting a simulator. but do whatever you want. i posted it for anyone.

[jakejm79]

I have just heard for some people it works and others it doesn't. I'm sure it has to do with the the overall state of the emissions system, not to mention different systems respond in different ways. I'd also be curious to see how it effected the fuel trims, since from my experience/research, it seems like with the T5 that the rear sensor is used to compensate for what the ECU might think is a failing front sensor.

[BobSaabit]

I don't see how it would work... wouldn't the ECU be expecting certain signals at certain engine temperatures and flows and throw a code when it sees a serious mismatch?

[Boatguy]

Why if you can turn your o2 off in t5 suite wouldnt you just change the rear o2 sensor hi and low limits to something it would never see? Im not sure if this is possible with t5 but i did it on mine in t7. i also had to adjust another setting, for which rpm the ecu uses the rear o2 instead of the front one. It was set at 1200-2800 rpms, i changed to 2 and 3 rpms

[BobSaabit]

Boatguy:

I see you're in MA... did you still pass the MA yearly ODBII check with this setting for the T7?

Could you be more specific about what setting you maxed to high and low limits for future reference? This could be very useful info to folks here.

Also, wouldn't you want to set those other RPM limits to like 2 and 20,000, so that you never hit the lower or the upper ranges and the rear sensor never gets queried? Seems that if the upper range is "3" that you'd hit it all the time.

Thanks,

[Boatguy]

I made these changes due to codes i was getting after installing a 3 inch downpipe and inefficient cat. My scanner says im ready for inspection, and no faults so far. Inspection due for me next week so ill let you know how it goes. I changed Catdiagcal.loadhi and catdiagcal.loadlo to 20 and 30 which eliminated my p0420 fault code. The other changes i made were to o2senspostcal. The description for those two are, the min/max engine rpm allowed for adap from rear o2 sensor. I chose 2 and 3 and its worked so far, i figured id surpass both while starting the car which would keep it from happening. I had been getting a persistent P0133 and had replaced the front o2 and reistalled the downpipe several times. Decided it was due to the rear o2 because the scanner showed the code always happening around 2000 rpm, which is when its adapting with that sensor. Hope this helps, will post if i win/lose at the inspection this week.

[Boatguy]

The changes i made to catdiagcal is the alternative to turning off the rear o2 in the t7suite pdf.

[BobSaabit]

Thanks... keep us posted (no pun). I'm interested in how it does on the test.

[jakejm79]

Thanks for the input Boatguy, it appears that those changes you made aren't an option for T5 cars though.

Having driven for about a week now with no rear o2 sensor, my CEL hasn't come back for a lean condition, so I convinced that the rear o2 sensor does influence fuel trim, especially combined with what the WIS states. If this is the case I will probably just disable it and then swap back in the stock DP and ECU at inspection time rather than risk having an erroneous simulated signal mess with my FT.

[BobSaabit]

Originally Posted by jakejm79

Thanks for the input Boatguy, it appears that those changes you made aren't an option for T5 cars though.

Having driven for about a week now with no rear o2 sensor, my CEL hasn't come back for a lean condition, so I convinced that the rear o2 sensor does influence fuel trim, especially combined with what the WIS states. If this is the case I will probably just disable it and then swap back in the stock DP and ECU at inspection time rather than risk having an erroneous simulated signal mess with my FT.

Jake... maybe save you some work: what's the test regimen in NH? Will they retest for free if you fail the emissions test? If so, I'd give it a shot with the simulator, then swap if you fail.

[jakejm79]

I think it depends on the place, but I seem to recall retests are discounted not free, but I could be mistaken, been a while since I haven't passed.