Odd O2 sensor behavior

[skid542]

I don't know if this is the right forum or if this should be in the electrical, but here it is anyways.

I'm getting my EM pretty well dialed but have come across a 'problem'. My EM is strictly fueling and is a piggy back that works by sending a modified signal through the MAF harness. This only really works if the ECU is operating in Open-Loop. Therefore I don't even have my 02 sensor hooked up - except the WB system but that's not tied into the ECU.

I've had no problems with my EM fighting the ECU and once I got the proper tuning tools/methodolgy sorted out. I have no check engine lights during cruise or WOT.

EXCEPT, if I pull a grade on the highway I start building boost (my turbo will make full wastegate boost by 2800) and so I'll be sitting there in 5th gear with my pressure around 5psi or so. If I keep this load condition for very long it will throw a CEL. On Vikash's modified Juice Box (V, if you see this thread - that Juice Box is the single best thing I have every bought for my car, thank you) it shows the CEL as being the EGO Sensor (so I assume it's the O2).

It doesn't cause any bucking or kicking, but it does through the CEL and then I have to clear it once I get up the hill and can clutch in, coast, and turn off the car. Once I clear the code and start the car back up it the CEL is gone and stays gone.

So my primary question - what does the ECU do when it sees an O2 sensor error? Obviously it's going to run in Open-Loop but does it do anything to timing or other fueling? Basically I'm trying to assess how critical is it to clear the code to keep it running well.

The second question, does anyone know what conditions are required under boost for the ECU to decide to run Closed-Loop? It was my understanding that under pressure the ECU runs Open-Loop but perhaps the TPS signal has a threshold to prevent the ECU from running Closed-Loop?

I guess ultimately I'm wanting to see what some of the others have seen or what their opinions are. I particularly am interested in those that are running a piggy back EM system.

Thanks in advance.

[Legacy777]

Lee,

I'm not sure I can directly answer your questions, but something I'd suggest doing is viewing the O2 sensor voltages, min/max O2 sensor voltages, and alpha correction data on the juice box.

It may not tell you anything, but it may help show whether there is a threshold that the ECU is seeing for example in the alpha corrections....that it throws a code once it's above a certain point.

[wtdash]

Since I'm working w/a piggy-back on an OBD2 car, I'll offer this....Have you tried running w/the 02 sensor hooked up? Since your EM only runs in Open Loop (OL), the ECU will just ignore it and use the O2 setting while in CL.

Also, when I had the Rev chip installed/w the O2 in the factory location, I'd get an O2 CEL in similar situations - long pulls up a grade. I never got around to asking Revtronix about it b4 they disappeared.

I'd bet the rate of change in the TPS signal affects OL vs. CL as does the RPM. On the NA OBD2 car OL occurs @ 4700 RPM, FWIW.

Td