Misfire, p0156, and p0161 - Mustang Evolution

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Old 01-28-2013, 07:12 PM   #1
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Misfire, p0156, and p0161

This is driving me crazy. I had the p0156 and p0161 codes and was planning to change the driver rear O2 sensor Sunday. On Saturday, I felt a misfire under a load. I changed the sensor, Sunday, and still have the misfire. The engine idles fine. I was going to let the codes disappear on their own after 50 starts. I scanned the system this afternoon and the two codes are still there and are the only codes. The scanner also showed "N/A 01/03" before giving the two codes. I checked the sensor wire as far as I could from underneath and could not find the wire from on top. I've read several online discussions and can't find a similar problem. Any ideas what to check next? I just turned 100,000 miles on my '02 GT.
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Old 01-28-2013, 10:01 PM   #2
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Fuse blown maybe check that first
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1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
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Old 01-28-2013, 10:15 PM   #3
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Is there a particular fuse to check? I did happen to look at the fuses in the box near the battery and saw no blown fuses. Thanks.
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Old 01-29-2013, 08:26 AM   #4
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P0156 indicates a problem with the passenger side rear O² sensor and has the same possible causes as P0136 (click here) . P0161 is a similar issue with the driver side rear sensor and has the same possible causes as P0135 (click here). Both are mostly power related/wiring issues.

The rear sensors have nothing to do with engine control, they just monitor the cats.

All four O² sensor heaters are powered from the same fuse, fuse #8 (20A) in the central junction box (under the dash)--as are the EGR Vacuum Regulator Solenoid, and the EVAP Canister Purge Valve and Canister Vent Solenoid.

Those could affect engine control, so check that fuse first...
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Old 01-29-2013, 05:55 PM   #5
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Thanks. That was good info. That fuse is good and there is no corrosion around it.
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Old 01-29-2013, 06:13 PM   #6
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Quote:
Originally Posted by escottcarp View Post
Thanks. That was good info. That fuse is good and there is no corrosion around it.
The misfire would be unrelated to those codes, as I said above all the rear sensor do is monitor operation of the catalytic converters--they have nothing to do with engine control. You'll need to crawl under there and monitor the sensor output and heater voltages.

This is a wiring diagram for DIY MIL Eliminators, however it also provide the wiring colour codes for the rear sensors.



With the sensor connected there should be 12 V between the heater wires at each sensor, just after starting the engine before the exhaust heats up. Once the car is running in closed-loop mode the voltage between the signal ground and signal + should vary between 0.1V and 0.6V every 2 seconds or so.
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-29-2013, 06:17 PM   #7
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Ok. Don't both of my codes apply to bank two and isn't bank two on the driver side? Bank one follows the #1 cylinder which is on the passenger side, yes?
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Old 01-29-2013, 06:26 PM   #8
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Quote:
Originally Posted by escottcarp View Post
Ok. Don't both of my codes apply to bank two and isn't bank two on the driver side? Bank one follows the #1 cylinder which is on the passenger side, yes?
Yes I got the codes mixed up previously. Both P0156 and P0161 are bank 2, sensor 2 (rear) codes.

Bank 2 is the driver side...

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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-30-2013, 11:24 PM   #9
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Concerning the misfire, the temperature is cold right now and I can count today's misfires on two fingers. Would cold weather have any impact on an engine misfiring?
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Old 01-31-2013, 05:10 AM   #10
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Concerning the misfire, the temperature is cold right now and I can count today's misfires on two fingers. Would cold weather have any impact on an engine misfiring?
It could, but it shouldn't. What engine mods do you have, if any?

Also, define "cold"? Here in NE Florida cold is 45°...
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Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
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Old 01-31-2013, 06:40 AM   #11
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No engine mods, just a Flowmaster exhaust. Here in Jackson, MS, cold is the same as north Florida. It was in the 40's yesterday. I figure I have a coil on the blink.
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