Closed Loop Fuel Enricher

[smithsrsn]

I think someone mentioned that it is the ECU that is limiting, not the sensor. Is that true?

 

Using the stock O2 sensor in the bellmouth would be my preference if the ECU could be altered to read into the 10's. I am suprised no one has attempted this yet.

 

It would make logging real easy and allow the use of the OBDII gauges without all the extra wiring and such.

[fahr_side]

I meant the target AFR compensation table the guy with the WRX said he had to flatten to keep his AFR from bouncing up and down far enough to affect driveability, here. Sounds like you're not having these issues.

 

@smithrsrn: Yes, the ECU has a table with the maximum rich value the AFR will read. On most of our cars it seems to be set at 11.02:1 which could be either the lowest value they are sure every sensor in production will reliably read to, or somewhere below where they expect the CL fueling will ever be mapped. I also guess the sensor will not accurately read down to 7.xx:1 like a typical WBO2 does. Remember the stock front O2 sensor is not a typical WB sensor with a linear output. You could try reducing the rich sensor limit in RR and try extending the scaling but somehow I don't think it's going to accurately read down to 10:1 AFR... it's just too much to hope for.

 

I'm considering this idea because the typical Bosch LSU sensors in most WBO2 kits don't seem to last that long in a permanent installation and I don't want to remove and replace the sensor every other week.

I might use a true WBO2 to scale MAF and tune fuel, with the factory O2 also in the bellmouth. I could then scale the stock sensor to match the WBO2, at least down to 11.02:1. I will be targeting a low of 11.2~11.5:1 AFR when my IC upgrade is in place so a rich limit of 11.02:1 should not be a problem.

[NSFW]

The guy that was reporting the oscillation issue has a 16-bit ECU, so it's not necessarily indicative of what happens with the 32-bit ECUs in our cars.

 

I have tried lowering the "rich limit" table, and extending the scaling downward, but the readings in the logger still bottom out at 11.2. There's another table somewhere that sets the limit, and it hasn't been defined yet.

 

That was actually one of my first quests when I started disassembling the ECU code, and I never did figure it out. I will take another shot at some point, but it's like looking for a needle in a haystack.

[fahr_side]

The guy that was reporting the oscillation issue has a 16-bit ECU, so it's not necessarily indicative of what happens with the 32-bit ECUs in our cars.

Right. Could be the extra delay between the upswing in AFR target and the O2 sensor seeing a corresponding rich dip was triggering further intervention to get AFR back on track, overshooting the mark, that triggering an equal but opposite reaction, overshooting again ad infinitum.

 

I have tried lowering the "rich limit" table, and extending the scaling downward, but the readings in the logger still bottom out at 11.2. There's another table somewhere that sets the limit, and it hasn't been defined yet.

 

That was actually one of my first quests when I started disassembling the ECU code, and I never did figure it out. I will take another shot at some point, but it's like looking for a needle in a haystack.

Ugh. I get dizzy just thinking about disassembling code.

[NSFW]

Right. Could be the extra delay between the upswing in AFR target and the O2 sensor seeing a corresponding rich dip was triggering further intervention to get AFR back on track, overshooting the mark, that triggering an equal but opposite reaction, overshooting again ad infinitum.

 

Yeah, and that sort of thing would not have surprised me at all after relocating the sensor like this. However I haven't seen any sign of it.