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Old 01-27-2008, 11:08 PM   #1
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Default Stock o2 Sensor failure?


I have recently switched to larger injectors (RC 440s) and "non-afm" mode of the MSPNP.

I have a wideband o2 sensor and gauge that is not connected to the MSPNP, just used for reference.

I have a the stock narrowband o2 connected to the MSPNP as well as to a split second AF gauge.

Before I switched the injectors, both the o2 sensors and the o2 readout in the Megatune all stayed in sync. Now it seems like the narrowband o2 is not working. The o2 readout in Megatune updates very infrequently, like 1 time a minute. The Split Second (narrowband gauge) also seems a bit 'frozen'. The sensor I have is heated, but the readings never seem to go any lower than 15AFR. The wideband is definitely working and the engine reacts to the tuning as expected.

I am just wondering if my stock o2 sensor might have failed, or if there is some issue with how it is wired. I am skeptical about the wiring being the problem because it worked fine before. I just wonder if the 20-30 minutes of the car idling very very rich while I tuned it somehow fouled the sensor.



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Old 01-27-2008, 11:16 PM   #2
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First of all, why don't you have the wideband connected to the MS?
You can foul sensors with too much carbon so that is a possibility. Having the wideband connected to the MS will help you reach the best possibly tune compared to the narrowband. Maybe with the new injectors you're running too lean/rich and the narrowband it maxed out of it's range.
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Old 01-28-2008, 02:00 PM   #3
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Default wideband

I definitely plan to use the wideband, but I am just trying to figure out why my narrow band is not working.

FWIW - It was surprising to me how accurately the narrowband sensor matched the wideband. The guages were matched tick for tick in my few hours of initial tuning when I first got the kit. I was almost disapointing. Not saying to trust a narrowband when tuning, but from what I saw, there would be no reason not to (unless of course your narrow band fails like mine has looked to do!)

Any other thoughts definitely appreciated.


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