Hello,

I'm currently an owner of an '04 RX-8, first time having any issues with my car, mainly with it running rich causing a flat line of my downstream O2 sensor. I already did a steam cleaning of the housing units (Yes I had it up to temp, held the rmps, and made sure my plugs were clean once cooled), I checked my EGR, timing, fuel pressure, injectors, and seals on the rotors themselves. The O2 sensor is new, same results as the old one, also my cat is not clogged. As for the Upstream O2, it is going way out of range, 7.82< in readings, but as I said, no lean code is being thrown to cause a rich condition to form. Any information would be great, if you need more information from myself I will gladly post more.

Thank you



'04 RX-8

Miles- 54,000

 

1: What do you mean by "flatline"? The rear O2 sensor is a narrowband sensor, so it returns either 0v (below 14.7) or 1v (above 14.7) only. At 14.7 it should oscillate between 0v and 1v, so if I interpret your "flatline" reference to some sort of graph where it is only showing 0v, meaning you are running at least slightly rich? What are the actual AFRs? If it's steady at 14.6, there isn't anything to worry about, but the rear O2 would show a constant 0v. Additionally, under a wide set of circumstances, the ECU will intentionally run richer than 14.7, producing the same result.
In short, the rear O2 isn't something to tune or troubleshoot with.

2: What out of range readings are you referring to on the front O2? It's wideband, so your ECU should be reporting an actual AFR number. Well, more than one, Commanded and Actual.

3: How did you "check the seals"? Do you mean you got it properly compression tested with compression scores for each face and normalized them to 250rpm at sea level? Or did you borescope the engine to look at the seals?

4: What method did you use to check your timing? I assume you mean ignition timing?


So far, it seems like you are jumping at shadows, since nothing you have listed seems to indicate a problem.

 

What is the driving conditions when this is happening? RPM and how hard are you accelerating?

I'm not trying to be mean guy, but I'm calling BS on at least some extent. Every programer I've plugged in only shows AFR of 10 at the lowest for the wide band. And command does drop down into the 9's but not lower then that.

So <7.82 is pretty hard to believe.

On top of that I haven't found an EGR on a RX8

What was your fuel pressure?

 

yeah, 7.82 is confusing. It can't be AFR, because the wideband won't read that low. It can't be voltage, since it's a 0-5v sensor. It might be mode 6 response time, but a low response time is the goal, so i don't see why he would be complaining that it's too low.

 

What is Mode 6 response time?

 

There is a series of tests built into the ECU (as part of the standard OBD2 protocols) which can be run to test various sensors. It will do things like cycling the O2 sensors to see how long it takes to move from lean to rich or rich to lean, how fast it response to a prompt from the ECU if it is told to get to a specific reading, etc...

Something like this is produced (this is a screenshot when you use the torque app to run it, but it can be run with any number of tools, as it's built into the ECU):

 

1. By flat line, I mean my downstream oxygen sensor is not reading a lean to rich change, but rather reading nothing is happening at all and staying at a 0.00 with no range positive or negative. Since my upstream is out of range (running too rich), looking at this issue within Ford, Mazda, and GM it shows how those two can correlate despite your downstream not truly affecting your lean to rich change. This was checked using a Span-On Modis EEM300

2. Right now I'm not home so I do not have the exact data for my fuel to air ratio

3. Seals were checked via a scope at first just for the apex seals. Once the engine was removed for the injectors inspection, they were checked again along with the face seals and compared to new seals. No issues were found

4.Timing was checked using the Span-On Modis EEM300 along with shutting off 'cylinders' to determine how those conditions would affect the readings. Timing was along done via a timing light which showed the same results was timing was in order.

Sorry, mistype, meant EVAP, not EGR

My fuel pressure was around 60 pis, within the range of 54-65 psi for sure. As for when it is an issue, all the time, idle to driving it normal, by normal I do mean normal driving, I do push it but not to a great degree, but does not matter, always running rich, as seen again from the Snap-On scanner

As for everything else I do need to wait until Monday when I can pull the live data again.

Thanks and no worries, I understand you need for info to get a better idea.

 

I'm sorry, I don't mean to offend, but your post makes things less clear, not more clear. If not for the "apex seal" references, I'd get the impression that you were trying to diagnose a big block V8 or something fairly standard.

There is still no indication that there is something wrong from what you are saying. If the front O2 is showing rich and the rear O2 is also showing rich, then they are at least agreeing, and there isn't a specific problem with either O2 sensor. And since there are plenty of valid conditions in which you would be running rich deliberately under command from the ECU, then unless you give us some AFR data on what you are running under what conditions (a data log would be useful), then there doesn't appear to be a problem.

Try to get a data log of idle, stable cruise, and wide open throttle pull in 3rd gear from ~3,000rpm to as high as you feel safe going. Log short term fuel trim, long term fuel trim, MAF g/s, RPM, commanded AFR, and actual AFR. I forget what data point you can grab for the rear O2, but get voltage or whatever value you can see for that.




BTW: A few of your methods are very concerning for a rotary... the "seal inspection" primarily.


Edit:
If your rear O2 never reads lean, even when the front O2 reads lean, like just after high RPM compete throttle lift-off, then it isn't a "running rich" problem, but rather more likely to be a wiring problem somewhere. If your actual AFRs never read lean and the two sensors agree, even when you are off the throttle, then it's going to be a hardware issue somewhere, like an injector stuck open, not software. I am not aware of any tuning that you could do on the stock ECU to produce fuel injection when you are completely off the throttle, and it certainly doesn't do it on the stock tune.

 

I think the main question is what is the problem? Just because you are trying to interpit what the o2 sensors are doing doesn't make a problem. Who cares if they appear to not be right if everything else is running great.

Is it running bad, do you get a flashing CEL, Bad fuel milage, does it not idle, do you have severe power loss? Basically what is the problem that you are trying to fix.