Cliffjumper126

Ok everybody! I got the information today! Here we go:
The LTFT at idle started out at 4.7 and went up to 8.6 over about 30 sec
The front 02/AFR at idle oscilates between .001 and .059mA

So what do y'all make of that?

roflcopter

iTrader: (2)

+4.7% or -4.7%?

And did you happen to see what the STFT was doing over that period as well? The LTFT shouldn't change quickly. And was this after being fully warmed up and such?

Also, it would be interesting to see your AFR over a WOT pull because my issue seems to not affect idle, but only the top end.

And those numbers are well within normal, same as mine. Which does not rule out the O2 because if the O2 thinks it's in the correct AFR range then it will report that and leave the fuel trims alone even if the actual AFR is far from being correct.

Cliffjumper126

There was no STFT because my rear 02 is disconnected. The car was fully warmed up and idling. The LTFT was at +4.7 when it was started then quickly over maybe a 20 sec span rose to +8.6 and stayed there. Is it supposed to be -4.7? I can't get readings during WOT because my buddy can't leave the shop with the scanner.

roflcopter

iTrader: (2)

You will still have a STFT, the rear O2 will not affect it at all. The direction that the fuel trim goes doesn't mean anything besides whether the car thinks it is consistently sitting slightly rich or slightly lean.

Could you reset your fuel trims then drive it for a day or so and get readings again? Also, it would be good to see if the car runs better right after resetting them.

Cliffjumper126

I don't know when my buddy will have time to help me again..but your request is exactly what I did today. I did reset my NVRAM and KAM this morning, and clear all my CELs (all this was after reconnecting the front 02), therefore the fuel trims would also have been reset this morning, then I drove the **** out of it for say half an hour with quite a few WOT runs, then I drove it normally the rest of the day before going over there. It didn't run any better right after resetting them. My STFT was indeed reading zero, and I know because I asked about it and he said it was because of the rear 02...but if that doesn't affect it, then why would it be zero?

roflcopter

iTrader: (2)

I have no clue why your STFT was reading 0, basically the function of the LTFT is to adjust the fueling tables to achieve a more consistently achievable match between actual and commanded AFR. The STFT is there to correct for the 'random' things that happen, the AC coming on, you giving it a little gas, a fuel injector not getting consistent supply. It will constantly fluctuate depending on what the front O2 sensor is reading as the actual AFR and responds to immediately to bring it closer to the commanded(hundreds of times a second). The LTFT is developed from a consistently positive or negative STFT, the ECU sees that it is a trend and changes the LTFT to get the STFT as close to 0 as possible(although it is never actually possible since this isn't a physics model).

I have no clue why your STFT would be sitting at 0, to me I would guess that your ECU is ignoring whatever data it gets from the O2, which should only occur if it thinks it is malfunctioning.

The way to see if that were the case would be to look at the Commanded AFR and compare it to the actual AFR at any given point. If the actual chases the commanded around, then the car is in closed loop and the STFT should be active. If the commanded just sits at a number then you know it is open loop and you need to figure out why it is always like that.

Now as far as your LTFT going to 8% pretty quickly and staying there with a 0% STFT would suggest to me that your car is thinking it is very lean and is trying to compensate causing your rich condition and power loss.

TL;DR

I'm leaning towards the O2 being bad. With the mileage on your car it would be a good idea anyways.

Cliffjumper126

I found a post on another thread stating that the STFT at idle should be 0%, + or - 1%. He said that if it was different at idle, it means you have a vacuum leak..and since mine was right on target, that possibility is now ruled out. I guess it jumping to 8% that quickly would still indicate that it thinks it too lean....

Another thing that confuses me is that wcs said earlier in the thread that the front 02 ranges 11.0 to 20.0 AFR and should be at 14.7 at idle...

Mine's not even in the range...unless its different units of measurement....HELP WCS!!

roflcopter

iTrader: (2)

Hmmm, it should be close to 0, but it should still jump around a tad. The big variances in it occur when you give the car a bit of gas. And you posted it being in mA, which is the raw data from it, while the numbers we are looking for are already translated into the actual ratio, such as 14.7:1.

I don't know how to do this conversion but maybe WCS will chime in on that.

nycgps

iTrader: (1)

what is the point of this thread again? didnt bother to read everything. have u check compression?

do a starter fluid test if u think u have a leak somewhere

Cliffjumper126

Oh ok yeah that makes sense. Hopefully he will. Yeah sorry about it being the raw data, that's all the computer shows lol

Cliffjumper126

We are trying to figure out why my car is running rich and experiencing power loss. Rofl's is doing a similar thing. The problems are not ignition related, and my compression is almost at spec so it's not the issue. We suspect our front 02/AFR sensors are failing. Starter fluid test?

nycgps

iTrader: (1)

spary some starter fluid somewhere that might have a leak, if your rpm jumps, you found the leak.

front O2 sensor ? just change it.

roflcopter

iTrader: (2)

I know for a fact that it is not an intake leak issue, I've had mine torn down to the lower intake manifold with all of the valves out and cleaned and reassembled and tested for leaks.

Cliffjumper126

I can't really test for leaks because
1.) I don't know if I have one
2.)much less where it could be

but the fact that my STFT reading wasn't jacked up at idle (it wasn't compensating for a leak) indicates that there is no vacuum leak, unless the STFT is indeed influenced by the rear 02, which is unplugged...

I plan to replace the front 02/afr, I was just hoping to figure out if it was indeed the issue before I dropped the mullah on a new one. Am I correct in thinking that the fact that my car ran no worse with the front 02/afr unplugged indicates that it is indeed the problem?

wcs

iTrader: (2)

Snapping the throttle should show a change in STFT.
If the STFT does not change you may have a baked A/F Sensor

wcs

iTrader: (2)

I'm leaning toward the A/F Sensor being hosed.
(Front O2 as we were incorrectly calling it, thank-you Harlan I hadn't realized how wrong that term was)
Because of the STFT not changing.

I'm still not entirely convinced you know what values you are reading with this computer (sorry).
But lets just say you are reading the current from out 4 wire heated A/F Sensor.

0 mA would indicate 14.7 AFR (stoichiometric point or lambda)
When you hit the gas you should see an instant spike in the STFT if you don't you may have a broken A/F Sensor.

Here are some short threads from the forum including a DIY on how to replace
https://www.rx8club.com/tech-garage-...change-227832/

https://www.rx8club.com/engine-tunin...-table-230104/

https://www.rx8club.com/tech-garage-...al-one-213443/

https://www.rx8club.com/series-ii-di...enewal-223163/

Here are some interesting articles
Wide Band Oxygen Sensors

Wideband O2 Sensors and Air/Fuel (A/F) Sensors <<<<-- diagnosis at bottom
We have a 4 wire Heated Air/Fuel sensor not a 5 wire Wideband O2 sensor

Here is a nice PDF on O2 sensor vs AFR Sensor (AFR starts on pg6)
http://www.autoshop101.com/forms/h37.pdf

Another good write with some diagnosis
air_fuel_ratio_sensor



lol you know if you owned a C.........

wcs

iTrader: (2)

AFR Sensor inspection from Mazda Workshop manual

FrontHeatAFRSensor_Inspection.pdf

BTW are you a auto or MT?

Cliffjumper126

I'm a 6spd manual of course, I would never have an automatic 8

I've ordered a better scanner for myself that can read live data and freeze frame data, so I can do all this on my own rather than depending on others. It'll be really useful with the 8 and its many mysteries haha

I know for a fact that I was indeed looking at the STFT, and it was zero. I guess I'm going to hold off on doing anything until the scanner comes in (it says monday). Then I can give y'all better readings because I won't be in such a hurry to get out of my friend's hair haha

Do we have 3 "oxygen sensors"? His scanner was showing 3 different ones.

wcs

iTrader: (2)

Only 2 in the exhaust

Cliffjumper126

Yeah that's what I thought and what I told him..dunno why it gave
readings for 3

I'll update once I get the reader next week

dannobre

iTrader: (3)

Usually a STFT of 0 means the car is in open loop. ( scanner should tell you open/closed loop status)

If the car is warmed up and in open loop you need to figure out why as part of your diagnosis

Quit worrying about your STFT numbers so much..they should be +/- to compensate for variables in engine parameters in the short term.

LTFT that are higher than 10 could mean that there is a problem with something...but even that on a 8 year old car isn't that big of a deal

If you are running on the original sensor...and the car is 6-7 years old just change it...you will likely save that much in gas over the longer term

Cliffjumper126

Yeah true about the sensor being old..and another thing, the previous owner drove the car with a failed cat (pieces of it in the exhaust), that could've killed the sensor too...

roflcopter

iTrader: (2)

Please keep us updated once you get the sensor replaced, I've been putting it off for a while and now have too many other projects that are zapping my money and the 8 is falling by the wayside, but it'd be good to know if that should fix it or not.

Cliffjumper126

I'll update as soon as the new reader comes in so we can compare 02 values

roflcopter

iTrader: (2)

Awesome.

Mind if I ask what scanner you got?

If it can actually get logs of a full pull and you can get it in a graph view with a few different parameters that will help a lot, although the information taken from that will basically only tell us if we are in fact having the same problem, not what the problem is.