P0122, running rich - an easier solution?

lparsons · Jul 3, 2023

First things first, the previous owner of my 98GT Convertible opted to remove the catalytic converters for the "custom exhaust" that they installed on this car. This of course is why the P0122 code is coming up, as the O2 sensors can't connect to anything if there are no catalytic converters.

It appears the car is compensating for this "lean" condition by running extra fuel. Oddly enough this doesn't seem to drastically reduce fuel economy but it does smell strongly of unburnt fuel.

The obvious solution to this would be to rebuild the entire exhaust system and put new catalytic converters in. I'll point out at this time that my state does not have annual inspections, so I don't need to worry about that. Is there another way that I could approach this, so that the car doesn't run so rich? Of course it would be great to make the check engine light go away but the focus here is more on the pervasive gas smell.

Suggestions?

It may be worth adding that every winter the car gets put away in a garage with the battery disconnected, so I'm confident it's not a transient computer issue going on here. Every spring when it comes out the error comes back up within a few minutes of driving, even without flogging it.

Shuttleman83 · Jul 5, 2023

Charcoal Canister can cause this also or sensors to it / vac lines. Rear o2's won't change anything, if it's missing front o2's yes.

Noobz347 · Jul 6, 2023

If I remember right, your 98 had four O2 sensors. 2 ea are pre-cat and 2 ea are post-cat.

You should be able to pick up what is called, a "Mil Eliminator" for the 2 post-cat sensors.

Over the years, I've seen mixed results with this approach.

Other alternatives would be to replace the Cats or get a custom tune.

lparsons · Aug 20, 2023

Noobz347 said:
If I remember right, your 98 had four O2 sensors. 2 ea are pre-cat and 2 ea are post-cat.

You should be able to pick up what is called, a "Mil Eliminator" for the 2 post-cat sensors.

Over the years, I've seen mixed results with this approach.

Other alternatives would be to replace the Cats or get a custom tune.

Today I finally made time to get under the car to install the MIL Eliminators. Interesting endeavour, that, with an interesting combination of plugs.

I then took it out for a drive. Check engine light was still on while I was driving around, and after restarting a couple times (to see if it would clear on its own).
I then put my code reader on it. Initially I had about 8 codes come out of it. The usual suspects of running too lean, plus a few others. I went ahead and cleared all the codes and drove around, it actually ran really well. I didn't flog it (I never do with this one) but it ran nice and never threw the check engine light. I couldn't smell the usual odor of running too rich, either.

Then I figured I should shut it off and turn it back on to see what it would do next. It started up with the check engine light on again. I put my code reader on it and saw (in no particular order)
P0141 O2 Sensor Heater Circuit Bad
P0174 System Too Lean Bank 2
P0171 System Too Lean Bank 1
P0161 O2 Sensor Heater Circuit Bad

If I clear the codes again with my reader, everything is great until I restart the car. It doesn't seem to come back with any normal amount of driving.

A quick look for "ford P0161" suggests the O2 sensor as the fault. I found when under the car that the sensors were just dangling in space (not a surprise as there are no catalytic converters in this car anymore). Is there anything similar to the MIL eliminator for those?

weendoggy · Aug 22, 2023

The two upstream O2's read the fuel trim (pre CAT), the two downstream (post CAT) confirm the upstream working. You need the upstream O2's in the exhaust to allow the ECU to monitor. You could run the MIL eliminator for the rear.

lparsons · Aug 23, 2023

weendoggy said:
The two upstream O2's read the fuel trim (pre CAT), the two downstream (post CAT) confirm the upstream working. You need the upstream O2's in the exhaust to allow the ECU to monitor. You could run the MIL eliminator for the rear.

Are there then two places on each side where the MIL eliminators could be plugged in? I'll admit I'm not intimately familiar with the exhaust systems on these cars (as I said the previous owner removed the cats before I bought it). I was working close to the transmission when I installed the MIL eliminators, I presume that is the rear location but I could be wrong. Would it be the same connections for both front and rear?

weendoggy · Aug 23, 2023

lparsons said:
Are there then two places on each side where the MIL eliminators could be plugged in? I'll admit I'm not intimately familiar with the exhaust systems on these cars (as I said the previous owner removed the cats before I bought it). I was working close to the transmission when I installed the MIL eliminators, I presume that is the rear location but I could be wrong. Would it be the same connections for both front and rear?

MIL's plug into the ECU harness for the O2's. The exhaust may not show an O2 bung if the previous owner didn't install them. I can only comment on my '02 that had the two pre-cat close to the engine and the post-cat were near the "H" connection nearer the rear of the transmission. I'd be checking a wiring diagram for your car to make sure you know what's what.

lparsons · Aug 23, 2023

weendoggy said:
MIL's plug into the ECU harness for the O2's. The exhaust may not show an O2 bung if the previous owner didn't install them. I can only comment on my '02 that had the two pre-cat close to the engine and the post-cat were near the "H" connection nearer the rear of the transmission. I'd be checking a wiring diagram for your car to make sure you know what's what.

Thank you, that helps a lot!

Would there be different OBD codes for the front and rear O2 sensors? That might help me sort it out as well.

weendoggy · Sep 8, 2023

The two codes showing Lean, was due to the O2's not being in the exhaust. When the engine was running all they did was monitor outside air and not fuel related exhaust. The other's are most likely due to the fact you said they weren't there. DUH!

P0122, running rich - an easier solution?

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