Multiple 02 Sensor codes and running rich - TCCoA Forums
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post #1 of 12 (permalink) Old 05-21-2018, 12:52 PM Thread Starter
JNT
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Multiple 02 Sensor codes and running rich

I been having ongoing issues with my second MN12 that I bought a couple of years ago.

96 4.6L stock

I originally had EGR codes and some others that would not go away. I finally traced this problem to a bent pin on the ECM touching one of the other pins. I replaced the ECM and the EGR code issue went away.

I am now having multiple 02 sensor codes. The car is now running very rich. It wasn't before.

I have done the following:
Replaced all 4 of the o2 sensors
cleaned maf
checked for vacuum leaks
tested the IAC
checked fuel pressure

I've checked for damage on the o2 sensor wires
I am able to see a signal from the 02 sensors using my scan tool so I'm not sure why it indicates a circuit issue.

The plugs are really fouled. I'm changing them this week along with the wires.

Codes

MIL on
P1132 Insufficient Switching 02S 1/1 Sensor Rich

Pending Codes
P0135 O2S Heater Ckt Malfunction 1/1
P0141 O2S Heater Ckt Malfunction 1/2
P0155 O2S Heater Ckt Malfunction 2/1
P0161 O2S Heater Ckt Malfunction 2/2
P1152 HO2S 2/1 Insufficient Switching Rich Mean

Any thoughts on this problem are appreciated.

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental

Last edited by JNT; 05-21-2018 at 10:44 PM.
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post #2 of 12 (permalink) Old 05-21-2018, 01:30 PM
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If the plugs are oil-fouled, the sensors are likely to be also.

Unplug the rear ones; in my experience, those foul first, bringing down the front ones somehow.

If most of the codes except the "catalyst efficiency" go away, you might try new ones.

I'd fix the oil source first; o2 sensors are expensive as a wear item.

I've heard vaguely you can clean them up with a torch, but I've never actually heard from someone that that worked, so .

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post #3 of 12 (permalink) Old 05-21-2018, 09:37 PM Thread Starter
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The plugs are not fouled with oil just carbon build up from running rich. I would agree that the o2 sensors may also be fouled now but they are were new maybe 200 miles ago so they shouldn't be. This all started happening suddenly and overall the car still runs surprisingly well despite running noticeably rich.

Will something besides a bad sensor or bad wiring cause an 02 heater circuit code?

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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post #4 of 12 (permalink) Old 05-22-2018, 07:15 PM
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There is a "HEGO" fuse for the heaters, which might be blown. The rear O2s go through the transmission harness, which goes under the dash. The front O2s go through the engine harness, via the bulkhead connector on the passenger side.

The front O2 harness is in one of the hottest areas of the engine bay; the wire insulation will often get brittle and break, causing shorts (had P1135/1155 a while back caused by this) to the O2s and (sometimes) EGR hardware.

Grab an EVTM and measure for continuity between each of the four O2 pins at the PCM connector with the O2s unplugged. That will tell you if there's a short anywhere in the harness. If you get a short, unplug the PCM harness from the engine/transmission harness and re-test each half separately, that will help you isolate where the shorts are. That was how I found my problem.
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post #5 of 12 (permalink) Old 05-22-2018, 11:17 PM Thread Starter
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I haven't disconnected the rear o2 sensors yet but I will. They were also replaced recently so they should be good unless damaged by how rich the car is running.

I'm seeing negative fuel trim numbers as low as -25% and the O2 sensor readings are usually around .7 - .9.

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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post #6 of 12 (permalink) Old 05-22-2018, 11:51 PM Thread Starter
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Quote:
Originally Posted by theterminator93 View Post
There is a "HEGO" fuse for the heaters, which might be blown. The rear O2s go through the transmission harness, which goes under the dash. The front O2s go through the engine harness, via the bulkhead connector on the passenger side.

The front O2 harness is in one of the hottest areas of the engine bay; the wire insulation will often get brittle and break, causing shorts (had P1135/1155 a while back caused by this) to the O2s and (sometimes) EGR hardware.

Grab an EVTM and measure for continuity between each of the four O2 pins at the PCM connector with the O2s unplugged. That will tell you if there's a short anywhere in the harness. If you get a short, unplug the PCM harness from the engine/transmission harness and re-test each half separately, that will help you isolate where the shorts are. That was how I found my problem.
I did check that fuse before and it was good. Testing for continuity is something I was going to do but then it occurred to me that it may not be necessary with what the code reader is telling me. If I'm data logging with my code reader and see voltage from the O2 sensors then doesn't that tell me that the wire between the sensor and the eec is intact?

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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post #7 of 12 (permalink) Old 05-23-2018, 08:34 AM
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Quote:
Originally Posted by JNT View Post
the O2 sensor readings are usually around .7 - .9.

Joe
While cruising, o2 voltages should fluctuate between .2 and .6, roughly speaking. .8-.9 is WOT territory (approx. 11:1-12:1), so very rich for a cruising state.

Al

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post #8 of 12 (permalink) Old 05-23-2018, 03:36 PM
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Actually the heaters are on separate circuits; if the fuse is good then you can check for 12V on the heater pins at the O2 connectors with them disconnected with the key on as well. That's why there are four wires: two for the heater, two for signal.

If you're seeing voltage on the O2s at the PCM then the signal wires would theoretically be intact. What voltage are you seeing on the two front O2s? Turn the key on without starting and see what the voltage is. Then see what it does after you start the car (it should NOT stay the same).

What PID are you using for those other O2 sensor readings?

-Brandon
97 Laser Red Thunderbird LX 162k, Stage 2 4.6L 2v N/A | 300 BHP (255 RWHP, 290 RWTQ) | 13.95 @ 97.58 | Build details | Pics at the Lorain Assembly plant
98 Black Mark VIII 160k, stock daily driver
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Gone but not forgotten: 96 Mark VIII, 94 Cougar XR7, 93 Mark VIII

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post #9 of 12 (permalink) Old 05-28-2018, 11:19 PM Thread Starter
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Quote:
Originally Posted by T6Rocket View Post
While cruising, o2 voltages should fluctuate between .2 and .6, roughly speaking. .8-.9 is WOT territory (approx. 11:1-12:1), so very rich for a cruising state.

Al
Thanks. Yeah I understand that number is indicating a rich situation I'm just not sure what is causing it.


Quote:
Originally Posted by theterminator93 View Post
Actually the heaters are on separate circuits; if the fuse is good then you can check for 12V on the heater pins at the O2 connectors with them disconnected with the key on as well. That's why there are four wires: two for the heater, two for signal.

If you're seeing voltage on the O2s at the PCM then the signal wires would theoretically be intact. What voltage are you seeing on the two front O2s? Turn the key on without starting and see what the voltage is. Then see what it does after you start the car (it should NOT stay the same).

What PID are you using for those other O2 sensor readings?
I do have 12v at the O2 connectors for the heater circuit. I have not used a meter to check for signal voltage at the PCM end yet. I have just been monitoring the voltages using a scan tool. While running it has usually been .7 - .9v and sometimes as high as 1V.

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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post #10 of 12 (permalink) Old 06-01-2018, 12:00 PM Thread Starter
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Quote:
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I do have 12v at the O2 connectors for the heater circuit. I have not used a meter to check for signal voltage at the PCM end yet. I have just been monitoring the voltages using a scan tool. While running it has usually been .7 - .9v and sometimes as high as 1V.

Joe
It occurred to me later that without a breakout box I can not check for o2 sensor voltage at the PCM while the car is running. I don't have any reason not to trust the voltages reported by the scan tool however.

The car now has new front 02 sensors and the rear sensors have been disconnected. I'm still getting the same 02 sensor codes. The idle is rough and fluctuating but it's not the IAC. I didn't think it was but swapped over a new one just to rule it out.

It feels like maybe there is a vacume leak somewhere but I can't find anything.

It also shows a new pending code of P1202 Cylinder No.1 Injector Circuit Open/Shorted I can feel this injector pulsing by holding my finger against it. I need to look up how to test the injector further.

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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post #11 of 12 (permalink) Old 06-10-2018, 06:50 AM
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check fuel pressure, it sounds like a mechanical problem
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post #12 of 12 (permalink) Old 06-10-2018, 03:56 PM Thread Starter
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I had checked the fuel pressure previously and it was fine.

Update on this. I ended up swapping in a new computer and that solved all of the issues.

Joe

1997 Thunderbird 4.6L LX (out of commission for now)
SCT XCAL 2 From Lonnie, 02 Mustang MAF and air box, Dynomax Cat Back Exhaust, Steeda U/D Pulleys, 70MM FRPP TB, Dual Piston Calipers, KVR Rotors, Alpine CD, Polk Speakers

1996 Thunderbird 4.6L LX Stock

1994 Thunderbird SC (Needs Work, for sale)
1996 Bronco XL - 2003 Escort ZX2 wrecked - 1996 Bronco XLT Sport

Project Car: 69 Lincoln Continental
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