Harlan

iTrader: (3)

Yeah you can unplug the rear o2. it will pop a CEL, but the ecu will stop using it during cruise too giving you better fuel economy (if it was the problem), it also allows you to control a wider band with the fueling tables.

BTW even after the CEL it takes the ECU a couple minutes to throw out the NB O2 data, so it will run rich for a couple minutes then default to the WB O2 for cruise.

Yeah, I know the knock sensor is being heard by the ECU, but I think at power it's listening for VERY loud knock and is deaf to the real thing. I haven't figured out exactly what's wrong with it, but I do know it will pick up any sharp noise as knock. I may play with it some more, but I have another knock control strategy right now. Really wish Oltmann was still around I have a ton of questions for him since he's one of the few that has actually dissected our ecu code.

Cliffjumper126

I unplugged the KS and fired her up. Popped a CEL, P0328 "Knock Sensor 1 Circuit High Input Bank 1 or 1 Sensor". Took her for a drive, doesn't run any differently except maybe it's more powerful (but it may just be me haha). I plugged it back in and drove back, and it still felt the same, no noticable loss in power (so it probably is me lol, unless it takes a bit to start pulling timing again). Could the KS be hearing the misfires from the 02 or AFR issue and be pulling timing? I'm running V-Power 93 so fuel isn't the cause. Hopefully I'll be able to get the AFRs and LTFTs today or tomorrow. Would unplugging the rear 02 screw with my AFRs and such? Oh, and I remember that I had a CEL for the rear 02 heater at one point a while back, but it never came back after I erased it...

Is our front 02 (or AFR) wideband? I was told it was narrowband. And if it's actually the issue, then unplugging the rear 02 could make things worse, therefore making it obvious what the issue is

wcs

iTrader: (2)

^^^ Front O2 sensor/AFR sensor is a wideband.

Ranges 11.0 AFR to 20.0 afr (+- 0.2)

edit
You know if you owned a Cobb AP ........................................

Cliffjumper126

Haha wish I had one! Well that means that we must've been reading the rear 02 sensor because the sensor we were reading was narrowband. I unplugged the rear 02, and I'll see what happens. I'm guessing the 11.0 AFR would be at idle and the 20.0 would be under load?

wcs

iTrader: (2)

noooooo

Idle should be 14.7
WOT low 13.1 to 12 high
20 if fuel cut off ... aka your foot is off the gas and the engine is revving down

edit
Basically 11.0 is pig rich and 20 is fuel cut (super lean)

Harlan

iTrader: (3)

Do not unplug the knock sensor. This will put the ecu in a sort of ignition limp mode. Unbolt the knock sensor from the block and leave it plugged in. Then reset the ECU.
Here is the first thread. I don't know if knock sensor data is in the NVRAM or KAM so reset them both.
https://www.rx8club.com/tech-garage-...r-reset-27548/
What you want to unplug is the rear O2 sensor, the one on the catalytic. I would zip tie the wire up to the plug so it doesn't drag on the ground or hit the cat.

If your WB o2 is messed up the NB will still control during cruise. The NB maintains the cycle around stoich so the catalytic can work, which is probably why it is used during cruise. NB O2 sensors are very sensitive around stoich.

Cliffjumper126

Ok wcs that makes sense, and will help once I find out what the readings are. Harlan, The knock sensor is connected now, and I will unbolt it ASAP. The rear 02 is now disconnected. What I was wondering is what will happen to my LTFTs and AFRs with the rear 02 unplugged, as well as what would happen with the rear 02 disconnected if the AFR/front 02 is faulty

Harlan

iTrader: (3)

Worst that should happen if the WB O2 is faulty is the car will go to +25% on STFT and give a new CEL. Remember wait about 5 minutes before taking your readings while driving. The ECU still has to timeout the NB O2 even if there is a CEL for the sensor.

Cliffjumper126

I can't take readings on my scanner (it's a cheap one)
I'll use my buddy's to do it when I can today or tomorrow, and I'll have driven more than 5 min by that point. I'll also keep an eye out for a new CEL indicating that it's running rich now that the rear 02 is disconnected

Thanks

roflcopter

iTrader: (2)

I've been having the same issue for a few months now and it seems like this type of thing that has just started cropping up in the community. Now I've done everything you have done as well and some more and have been leaning towards a possible WB O2 issue as well but haven't dropped the money to test it yet. I'm looking forward to seeing if it fixes your issue.

For what it's worth my Fuel Trims are quite normal(never goes about 8% in either direction ST or LT at idle or cruise) but after taking some datalogs while doing WOT pulls it seems that the issue happens right as the car is coming out of closed loop, which does in fact point to an O2 issue.

Harlan

iTrader: (3)

While in cruise the NB O2 does not actually play with fuel trims, instead it changes the demanded AFR. It's very counter intuitive and downright bizarre, but that's how it works.

Cliffjumper126

I have noticed that it seems to run better now that the downstream 02 is unplugged. My ever-present P0301 misfire is gone as well (for the moment). My car still lacks power between say 5k and 6500. Another thing I noticed is that while accelerating under say 1/4-1/2 throttle the car stops accelerating for a split second and jerks (then it starts accelerating again, just has power loss) at 5k and at about 6250 (after this second pause/jerk, power comes back). This is in 1st, in all other gears power loss starts at 4500. At full throttle there is no jerking just the power loss between 5-6250.

Cliffjumper126

P0301 Came back
Rear 02 wasn't the root of the issue apparently, I NEED to get those readings tomorrow. Will keep y'all updated

Harlan

iTrader: (3)

Clean/replace plugs. You've been running rich for a while chances are they are badly fouled. Also, if you haven't already you need to check/change coils and wires.

Oh and at least you know your front O2 sensor is ok, they are EXPENSIVE.

Cliffjumper126

Yeah my plugs will need replacing, they are black lol. I wanted to get the jerking/power loss fixed first though. How do you know that my front 02 is ok? Because it's didn't throw a CEL for running rich? If that's the case, then what could be causing the jerking/power loss I described above? That was happening when my current plugs were new, so they aren't the cause (I also replaced the coils and wires at the time, so they aren't the issue either). I did find a correct front 02 replacement on Amazon for $167, the same one Advance Auto had for $274 or whatever it was.

roflcopter

iTrader: (2)

I would not rule out the possibility of the front O2 being bad, I'm suspecting mine while fuel trims and AFR looks good under normal conditions but has a rich condition upon going open-loop. Just because the numbers are right doesn't mean that it's not just compensating on the other end.

Do you know anyone who would let you trade O2's for a day and see what happens?

Cliffjumper126

Unfortunately, I don't know anyone around here who has an 8, so I may end up having to buy one . I could probably say it was the wrong one and return it if it didn't do any good. I would buy the one from Amazon of course. I'm going to get my readings first though, hopefully tomorrow afternoon.

When does it go open-loop?

roflcopter

iTrader: (2)

It goes open-loop usually between 5k-6k at WOT, you'll notice the STFT drop to 0 and the commanded AFR flatline to stoich when it happens.

wcs

iTrader: (2)

^^^^^The commanded AFR flat line to stoich at OL?
I don't think this makes sense.

Did you type it from a phone?

Cliffjumper126

A friend of mine suggested I unplug the AFR/front 02 and see if it makes a difference. I feel like something may happen (hell it may not even run) but it wouldn't tell me anything useful would it? Oh and I unbolted the KS and reset the NVRAM and KAM

wcs

iTrader: (2)

If you unplug the WB O2 you are going to force the ECU in to Open Loop

roflcopter

iTrader: (2)

No, the commanded AFR will sit at stoichiometric(14.7) while in open loop. The ECU is not looking at the commanded AFR anymore and is working straight from the load based fueling tables. It's the easiest way to tell if the car is open or closed loop while looking at plots.

https://www.rx8club.com/trouble-shoo...tumped-240783/

My thread has plenty of data in it showing this as well as datalogs of my car driving with the front WB O2 sensor disconnected. As you can see a few posts down from the top, it doesn't appear to fix the problem, although it does mask it because the transition to open loop isn't there so the power loss isn't as sudden.

Cliffjumper126

So I unplugged the AFR/front 02 and the car drove the same. No worse, no better. The power loss was still there but it didn't seem to jerk as much. For example, I was going up a hill in second and the RPMs were climbing normally until they got just over 4500, then they started slowing their climb and stopped climbing at about 5200. Doesn't matter if I floor it either, they stay there. So I upshift to continue accelerating lol. If the sensor was good, wouldn't there be a difference in how it ran with it unplugged?

wcs

iTrader: (2)

Aaaaahhhhhhhh ok

roflcopter

iTrader: (2)

Not necessarily. If the O2 sensor is broken causing the car to run rich then running the car without it wouldn't produce a different result than the car defaulting to a richer fueling table due to the O2 not being present.

This almost more points that the O2 is messed up because the car should run worse with it unplugged.