Secondary O2 Sensor Delete?

[lsfourwheeler]

Has anyone deleted their secondary (post-cat) O2 sensor? I'm current working on my exhaust modifications for my EJ207 and I wanted to run without the rear O2 sensor because I haven't put the bung for it in yet. From what I can tell, 16bit ECU cars don't use the secondary O2 sensor for any fueling related calculations and I'm not running a cat so the secondary is essentially useless for me.

This said, no matter what codes I delete and with the O2 sensor is unplugged or plugged in (but not in the exhaust) I still get a flashing CEL. When I delete the codes I get no codes on the code reader but still a flashing CEL. CEL on means IAM (Ignition Advance Multiplier) drops to zero when driving and causes boost to be wastegate pressure only as a failsafe.

Seems like this shouldn't be so hard?

[STiPWRD]

I'm running without the rear O2 sensor and deleted codes. I'm not getting any CELs and seems to drive fine. My ECU is 02 wrx. Are you using a JDM ECU?

[lsfourwheeler]

I'm running without the rear O2 sensor and deleted codes. I'm not getting any CELs and seems to drive fine. My ECU is 02 wrx. Are you using a JDM ECU?

Yes, but I'm using a JDM Forester ECU because the place I bought the EJ207 from messed up...I'm concerned that there is some inherent compatibility issue with the ECU or something that I'm missing. I flashed a stock V8 EJ207 rom on it and the engine runs well overall, just this weird O2/IAM issue that I can't seem to fix.

I have logs and the ROM if anyone thinks something in there might be helpful. I don't see anything that really helps me diagnose the issue.

[STiPWRD]

Sorry I can't help much with a JDM ECU. You could fool the ECU into thinking there is a rear O2 installed by hooking up a resistor to simulate the heater and a 0-1V voltage source across the other two wires to simulate the signal. Or you could literally hook up a normal rear O2 sensor to the harness but not install it in the exhaust stream - this is equivalent to putting in a bung spacer. The rear O2 0-1V voltage just needs to be different than the front 0-1V signal over time to make the ECU think there's a cat there causing a difference.

[lsfourwheeler]

Sorry I can't help much with a JDM ECU. You could fool the ECU into thinking there is a rear O2 installed by hooking up a resistor to simulate the heater and a 0-1V voltage source across the other two wires to simulate the signal. Or you could literally hook up a normal rear O2 sensor to the harness but not install it in the exhaust stream - this is equivalent to putting in a bung spacer. The rear O2 0-1V voltage just needs to be different than the front 0-1V signal over time to make the ECU think there's a cat there causing a difference.

I tried hooking up the O2 sensor but not having it in the stream. I tried with and without deleting the codes and in both cases I still have a flashing CEL but no codes for misfire or knock in the log.

[Ajzride]

You could try and O2 simulator.

http://www.bigdaddiesgarage.com/straight-cel-fix.html

[STiPWRD]

I tried hooking up the O2 sensor but not having it in the stream. I tried with and without deleting the codes and in both cases I still have a flashing CEL but no codes for misfire or knock in the log.

Are you positive the rear O2 is causing the flashing CEL?

[lsfourwheeler]

Are you positive the rear O2 is causing the flashing CEL?

No, I'm not sure. But that is the only identifiable thing the ECU has complained about thus far. AVCS is wired properly and the rest is stock EJ205 wiring which should be compatible.

[Bob_n_Cincy]

Sometimes if you leave the diagnostic plugged together it will cause a CEL blinking. (2 green connectors)
Bob

[lsfourwheeler]

The test connectors are disconnected. I'm running the same way I ran the car with my EJ205 but with the new ECU and AVCS wired now.

[lsfourwheeler]

Well, it's not the O2 sensor setup. Got the finished exhaust in this past weekend. Going to try swapping the ECU to see if that fixes it. Maybe the one that came with the engine is no good.

[lsfourwheeler]

Turned out the check engine light (yet no associated codes) was caused by the IAT sensor in the EJ207 intake manifold below the throttle body. For whatever reason, if you have both the MAF one and the Ej207 sensor then things get wacky. This was somehow not very easy information to find in forums which is strange considering how common the swap is.

But anyways, I found it and I now have a properly running engine :)