Code 42 Oxygen Sensor
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Freshman User
Joined: Dec 1999
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From: Lisbon Falls USA
Code 42 Oxygen Sensor
Anyone have any good information on Code 42. I have a 85 Bronco II with a 2.8 and feedback carb. Got this code and checked out the sensor. I used a digital meter as I did not have an analog one. I can see the sensor start generating a signal as it gets hot. It goes from about .01 volts DC up to about 1 volt then the sensor tapers off to about .5 and moves up and down about .1 volt above or below. Since the digital meter is averaging the signal I assme that the sensor is working OK. I checked the wiring and that checked out fine. The engine seemed to be up to temp and I did run it for 2 minutes at 2500 rpm to heat up the sensor. The temp outside was 32 degrees. The ECM generates only one other code. Code 13 because I have the engine final rpm set a little higher then what the ECM runs it at. Could this be giving the code???
Since the O2 sensor is the original and it has 140,000 on it I decided to replace it. The new sensor is giving the same code & readings to the ECM.
The system passed the KOEO test. The code 13 & 42 are generated during the KOER test.
Might anyone have soem help on this one??
Since the O2 sensor is the original and it has 140,000 on it I decided to replace it. The new sensor is giving the same code & readings to the ECM.
The system passed the KOEO test. The code 13 & 42 are generated during the KOER test.
Might anyone have soem help on this one??
Postmaster
Joined: Dec 2001
Posts: 3,742
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From: UT
If you can get a hold of a pinpoint test, that will give you a systematic way of diagnosing the issue. Try going to the library. You can often find a proper repair manual in the reference section. I'd have more ideas, if you had a multi port fuel injected engine, but I'm just not very good with carbs.
Thread Starter
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Freshman User
Joined: Dec 1999
Posts: 48
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From: Lisbon Falls USA
Give me the ideas you have for the multi port injection. The principles are identical for either. The feedback carb was Ford's intro into fuel injection. They built the computer end of it first and applied the controls to the carb.
Postmaster
Joined: Dec 2001
Posts: 3,742
Likes: 2
From: UT
Alright...
1) fuel pressure/fuel delivery. If the pressure is too high, you get too much fuel injected into the intake. In general check the fuel delivery system.
2) air flow restricted so there isn't enough air. wouldn't be very common, but carbs do have chokes, and the purpose of a choke is to close off air intake.
3) along the lines of 2, anything that makes the computer think there is more air coming in than actual (bad MAF or MAP signal)
4) and my final thought, a bad PCM. I actually had this very issue once on a late '80's Chevy I had. Code 42 that I couldn't figure out. After paying someone to diagnose it (interesting story, maybe sitting around the campfire I'll tell it), the problem turned out to be a fault in the PCM.
1) fuel pressure/fuel delivery. If the pressure is too high, you get too much fuel injected into the intake. In general check the fuel delivery system.
2) air flow restricted so there isn't enough air. wouldn't be very common, but carbs do have chokes, and the purpose of a choke is to close off air intake.
3) along the lines of 2, anything that makes the computer think there is more air coming in than actual (bad MAF or MAP signal)
4) and my final thought, a bad PCM. I actually had this very issue once on a late '80's Chevy I had. Code 42 that I couldn't figure out. After paying someone to diagnose it (interesting story, maybe sitting around the campfire I'll tell it), the problem turned out to be a fault in the PCM.
Thread Starter
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Freshman User
Joined: Dec 1999
Posts: 48
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From: Lisbon Falls USA
Fixed
Thought I'd post this in case anyone else ever runs into this problem. The code 42 means that the ECM detects that the oxygen sensor is reading on the rich side during the KOER test. The engine seemed to run fine so the problem was not obvious enough to find. After a lot of troubleshooting I found that the power valve on the carb was leaking fuel through the diaphram. The power valve is connected to intake manifold via a 1/4" vac hose. The excess fuel was leaking into the intake and causing the oxygen sensor to always read rich. The reason the engine did not notice any significant trouble was the ECM was directing the feedback solenoid to trim the rich fuel condition which stabilized the engine operation. It appears that this one could go on for a long time without the driver seeing any major issue except the drop in fuel economy.
One would think that the vehicle would see a performance drop when you step into it. It appeared that because of where the valve vac line was attached to the intake as you stepped into the engine the vac increased across the leak and gave the engine the extra fuel which masked the fact the valve was faulty.
One would think that the vehicle would see a performance drop when you step into it. It appeared that because of where the valve vac line was attached to the intake as you stepped into the engine the vac increased across the leak and gave the engine the extra fuel which masked the fact the valve was faulty.
