Part-throttle bucking P0505 no o2 Voltage

K-Series Programmable ECU installation questions / support issues
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Ah_03EP3
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Joined: Wed Feb 05, 2025 3:10 pm

Part-throttle bucking P0505 no o2 Voltage

Post by Ah_03EP3 »

Hi all,
2003 Civic Si
K20a3
Injen Cai - Skunk2 Pro ser. 70mm TB - Skunk2 Pro ser. IM
IACV delete (incompatible with TB) & iacv disabled in settings
HKS Hi-power catback w/ stock headers
Newly installed Acuity Hall effect TPS (last week)

I've been having intermittent part throttle bucking for about 6 months now. I noticed it seems to happen more on tip with very light throttle what feels to me like 2-4% (but no logs). Initially the CEL was P1106 but after replacing the old tps with the acuity the bucking behavior comes back with CEL for P0505. Idle air? I have been running this hardware setup without an IACV for over 3 years with no issue before running into problems with these codes and jerkiness.

I noticed my primary o2 sensor is reading a constand 0V and -37 mA. Replaced the o2 today to see if I could get a reading but nothing. Possible wiring issue with the primary o2?
I haven't been able to capture any logs of the bucking behavior yet (except for a log in neutral where the rpms seemed to be bouncing off 2k adding and removing fuel rapidly) which is not exactly the same as when i'm driving but could be related. I will post that log when I get my computer,

Thanks!
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Spunkster
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Re: Part-throttle bucking P0505 no o2 Voltage

Post by Spunkster »

Post the calibration and a datalog made with that calibration showing the issue.
Ah_03EP3
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Joined: Wed Feb 05, 2025 3:10 pm

Re: Part-throttle bucking P0505 no o2 Voltage

Post by Ah_03EP3 »

The Kal and Log
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Spunkster
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Re: Part-throttle bucking P0505 no o2 Voltage

Post by Spunkster »

Have you tried your ECU on a known working vehicle with their calibration loaded?
Ah_03EP3
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Joined: Wed Feb 05, 2025 3:10 pm

Re: Part-throttle bucking P0505 no o2 Voltage

Post by Ah_03EP3 »

I haven't as I don't know anyone with an Ep3 or Rsx that's local and the car is my daily so I need to use it for work 5 days a week. Maybe a Honda tuner would have either car in their shop that's compatible with my ecu to test with?
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Spunkster
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Re: Part-throttle bucking P0505 no o2 Voltage

Post by Spunkster »

You should try to find someone locally to test this as it will help you determine if it the ECU or the vehicle that has the issue.
Ah_03EP3
Posts: 4
Joined: Wed Feb 05, 2025 3:10 pm

Re: Part-throttle bucking P0505 no o2 Voltage

Post by Ah_03EP3 »

Thanks for the quick replies Spunkster, I'll try posting around online and stuff about testing the ECU. In the meantime I'm going to try reenabling the IACV and see if that helps with anything
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