P0420 & P0430 on the Taurus

Update time:

Replacing the primary and secondary o2 sensors appears to have resolved the problem. I replaced them over the weekend and the car has not given me a CEL of any kind since. I also replaced all 6 spark plugs as they were due for service as well, 75k miles.

Results from Torque:



Everything seems to be working good on first start after everything was done.



This is me driving around. The hills and valleys are shift points.



And the car coming to a stop.



Slowing down, accelerating, then slowing down again.

Connor2712 said:

He was saying that that's the price he bought them for himself.. also check RockAuto they have them for way less.

As for the technical question the usual culprit is O2 sensors. Running rich is usually what messes them up, as Q already pointed out. No other issues with the motor?

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Yes, I replaced the catalytic converters myself last time. I bought them from one of my local Ford dealerships and did the work myself.

Buying CATs from RockAuto, that's the first place I go to for all my vehicles' mechanical needs. I'm in California. The problem there is that the CATs that RockAuto has available are all EPA certified, and me being in California means that they need to be CARB certified, not EPA certified. That said, I cannot buy CATs for my Taurus from RockAuto, they have to be from Ford.

The lesson I learned about this is to replace the o2 sensors first if this P0420 and / or P0430 CEL happens again. Particularly if the CEL turns off and on as it was doing this time. The time I replaced the CATs (as referenced in my OP), the CEL was always on.

And no, there's no other issues with the motor.

After almost two weeks of being free of P0420 and P0430, it has returned.

I guess this means that I do indeed need to get new CATs for my Taurus? Any other suggestions before I break down and spend $2,000 on catalytic converters?

CDsDontBurn said:

After almost two weeks of being free of P0420 and P0430, it has returned.

I guess this means that I do indeed need to get new CATs for my Taurus? Any other suggestions before I break down and spend $2,000 on catalytic converters?

View attachment 219650

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When you clear your DTCs, problems can still exist in the car, but the CEL won't come back on until you complete a drive cycle. Sometimes this can take several days and/or many miles if you don't know the exact criteria for the cycle. Once the drive cycle is completed, and if problems still exist, codes will be thrown again and the CEL will come back on. Many people think that CEL off = no problem, but this is only true when the drive cycle is complete. In most scan tools you can monitor when drive cycle is complete (various system monitors ready).

Perform a temperature differential check on the cats using a cheap infraed laser thermometer. If the temperature at the cat inlet is significantly higher that at the outlet (200 degrees or more) then your cat is clogged up.

Before replacing your cats again, monitor commanded AFR vs. actual AFR. As someone above correctly pointed out, if the car is running rich it will drastically shorten the life of your cats.

Also, I would first try cleaning the cats. People scoff at this, but it does work (around 60% of the time). You can clean the cats by removing the O2 sensors and spraying SeaFoam into the bungs. Spray a lot, at all different angles, to soak the insides of the cats to the greatest extent possible. Replace the O2 sensors and let the car sit for 2-3 hours before starting it. When you do start it, be prepared for it to smoke like Cheech & Chong through the exhaust for 20-30 minutes as the SeaFoam burns off. Then, without clearing DTCs, complete a drive cycle and see if the CEL turns off on its own.

If you do end up having to replace your cats, I would check CarID for pricing (once the page loads hit CTRL+F and search for "interceptor"). I've been very pleased with CarID's prices on many things (including cats for 2 different cars), as well as their fast shipping and excellent customer service.

Sorry guys, I'm not on here much.

kekaye56 said:

Have you performed any pressure checks on the exhaust system?

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How do I go about doing this?

XLR8 said:

Log commanded vs. actual AFR.

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Please explain further. I'm not familiar with either of these. Is this something I can do from Torque?

XLR8 said:

When you clear your DTCs, problems can still exist in the car, but the CEL won't come back on until you complete a drive cycle. Sometimes this can take several days and/or many miles if you don't know the exact criteria for the cycle. Once the drive cycle is completed, and if problems still exist, codes will be thrown again and the CEL will come back on. Many people think that CEL off = no problem, but this is only true when the drive cycle is complete. In most scan tools you can monitor when drive cycle is complete (various system monitors ready).

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That's what I showed in my last post. The drive cycles had been completed and shown as complete per Torque Pro app as shown in my post where it had been resolved.

XLR8 said:

Perform a temperature differential check on the cats using a cheap infraed laser thermometer. If the temperature at the cat inlet is significantly higher that at the outlet (200 degrees or more) then your cat is clogged up.

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I have one of those. I can do this.

XLR8 said:

Before replacing your cats again, monitor commanded AFR vs. actual AFR. As someone above correctly pointed out, if the car is running rich it will drastically shorten the life of your cats.

Click to expand...

Again, I'm not sure what commanded AFR and actual AFR is, so I'll need clarification on this before I can test / check for this.

XLR8 said:

Also, I would first try cleaning the cats. People scoff at this, but it does work (around 60% of the time). You can clean the cats by removing the O2 sensors and spraying SeaFoam into the bungs. Spray a lot, at all different angles, to soak the insides of the cats to the greatest extent possible. Replace the O2 sensors and let the car sit for 2-3 hours before starting it. When you do start it, be prepared for it to smoke like Cheech & Chong through the exhaust for 20-30 minutes as the SeaFoam burns off. Then, without clearing DTCs, complete a drive cycle and see if the CEL turns off on its own.

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Spraying SeaFoam into the primary bungs won't be an issue. However:

1. Is there any way to easily get to the firewall side primary o2 sensor without removing the upper intake manifold?
2. After dousing the CATs in SeaFoam, do I need to reinstall the o2 sensors and button everything back up before starting the car again? Or do I need to start the car with the primary o2 sensors removed?

XLR8 said:

If you do end up having to replace your cats, I would check CarID for pricing (once the page loads hit CTRL+F and search for "interceptor"). I've been very pleased with CarID's prices on many things (including cats for 2 different cars), as well as their fast shipping and excellent customer service.

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I'll check with CarID. But if they only sell EPA certified CATs, I cannot purchase them from CarID as that would make them illegal to use in the "wonderful" state of California where I reside. The CATs I purchase must be CARB certified. I ran across this when I was looking at RockAuto for pricing on replacement CATs.

I've condensed your questions to make responses easier:

CDsDontBurn said:

Please explain further [about AFR]. I'm not familiar with either of these. Is this something I can do from Torque?

[...]

Again, I'm not sure what commanded AFR and actual AFR is, so I'll need clarification on this before I can test / check for this.

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AFR is air-to-fuel ratio. In the ECU, and in most scan tools/data loggers, it's usually expressed in lambda. Lambda is essentially a multiplier of stoichiometric ratio (called "stoich"), which is 14.64:1 (14.64 parts air to 1 part fuel, by volume). Stoich is the most efficient (cleanest) burn for emissions, but not optimal for performance. If you read a lambda of 1, then you're at stoich (1 * 14.64 = 14.64). Stoich is generally what you should see when the ECU is operating in closed loop (usually idle and low/part throttle). At high and wide-open throttle (WOT), the ECU will switch to open loop and command a different (non-stoich) lambda/AFR. In open loop operation you may see a lambda of something like 0.853, which is an AFR of 12.5:1 (14.64 * 0.853 = 12.5, or, 12.5 parts air to 1 part fuel, which is richer than stoich). Many scan tools/data loggers (I don't know about Torque) can show you the lambda the ECU is commanding and the actual lambda that is occurring in the engine. If the actual lambda you're seeing at idle or low/part throttle is lower than 1, then the engine is running rich (greater than 1 is running lean). If you see a commanded lambda that is consistently and significantly different than actual lambda, you know that for some reason the engine is not achieving the AFR being commanded by the ECU.

Another way to tell if your AFR is correct (as commanded by the ECU) is to monitor your short term fuel trims (STFM). When you watch STFT, the numbers will tell you what's happening with your AFR. If the STFTs are constantly negative numbers, it means the ECU is trying to pull fuel (run leaner/increase AFR) because the engine is running richer than the ECU wants it to. Likewise, if the STFTs are constantly positive numbers, it means the ECU is trying to add fuel (decrease AFR/run richer) because the engine is running leaner than the ECU wants it to. It's normal to see STFTs fluctuate somewhat as the ECU is constantly adjusting to maintain the desired AFR, but if you see constantly positive or negative STFT numbers, it usually indicates that the ECU is struggling to add or reduce fuel because the engine is not running at the ECU's desired AFR. In the same way you monitor STFT, you can also monitor long term fuel trims (LTFT). LTFTs are essentially an average of STFTs over time, thus should fluctuate much less and much more slowly than STFT. If you monitor both STFT and LTFT simultaneously, and you see LTFTs fluctuating with frequency similar to STFTs, that's almost always a sign of a bad cat.

CDsDontBurn said:

Spraying SeaFoam into the primary bungs won't be an issue. However:
1) Is there any way to easily get to the firewall side primary o2 sensor without removing the upper intake manifold?
2) After dousing the CATs in SeaFoam, do I need to reinstall the o2 sensors and button everything back up before starting the car again? Or do I need to start the car with the primary o2 sensors removed?

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1) Not really. There are ways you can get to it without removing the intake, but it's much more trouble than it's worth. There are creative ways that you can reach the sensor to turn it with a wrench, but it can be a nightmare to (a) reach the plug and squeeze the tab to disconnect, and (b) re-thread the sensor when you're done.

2) Yes, reinstall the sensors as normal before starting the car.

CDsDontBurn said:

[...]that would make them illegal to use in the "wonderful" state of California where I reside. The CATs I purchase must be CARB certified.

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I can't help you with that. Ugh, CARB. Come to Texas. A WHOLE LOT of your neighbors are doing that. There are some surprisingly easy and inexpensive ways around your issue, but (a) they're just as illegal as buying non-CARB cats, and (b) they won't actually fix the problem (they'll just make the codes go away and stay away, but your car would still fail a tailpipe sniffer test).

XLR8 said:

AFR is air-to-fuel ratio. In the ECU, and in most scan tools/data loggers, it's usually expressed in lambda. Lambda is essentially a multiplier of stoichiometric ratio (called "stoich"), which is 14.64:1 (14.64 parts air to 1 part fuel, by volume). Stoich is the most efficient (cleanest) burn for emissions, but not optimal for performance. If you read a lambda of 1, then you're at stoich (1 * 14.64 = 14.64). Stoich is generally what you should see when the ECU is operating in closed loop (usually idle and low/part throttle). At high and wide-open throttle (WOT), the ECU will switch to open loop and command a different (non-stoich) lambda/AFR. In open loop operation you may see a lambda of something like 0.853, which is an AFR of 12.5:1 (14.64 * 0.853 = 12.5, or, 12.5 parts air to 1 part fuel, which is richer than stoich). Many scan tools/data loggers (I don't know about Torque) can show you the lambda the ECU is commanding and the actual lambda that is occurring in the engine. If the actual lambda you're seeing at idle or low/part throttle is lower than 1, then the engine is running rich (greater than 1 is running lean). If you see a commanded lambda that is consistently and significantly different than actual lambda, you know that for some reason the engine is not achieving the AFR being commanded by the ECU.

Another way to tell if your AFR is correct (as commanded by the ECU) is to monitor your short term fuel trims (STFM). When you watch STFT, the numbers will tell you what's happening with your AFR. If the STFTs are constantly negative numbers, it means the ECU is trying to pull fuel (run leaner/increase AFR) because the engine is running richer than the ECU wants it to. Likewise, if the STFTs are constantly positive numbers, it means the ECU is trying to add fuel (decrease AFR/run richer) because the engine is running leaner than the ECU wants it to. It's normal to see STFTs fluctuate somewhat as the ECU is constantly adjusting to maintain the desired AFR, but if you see constantly positive or negative STFT numbers, it usually indicates that the ECU is struggling to add or reduce fuel because the engine is not running at the ECU's desired AFR. In the same way you monitor STFT, you can also monitor long term fuel trims (LTFT). LTFTs are essentially an average of STFTs over time, thus should fluctuate much less and much more slowly than STFT. If you monitor both STFT and LTFT simultaneously, and you see LTFTs fluctuating with frequency similar to STFTs, that's almost always a sign of a bad cat.

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Had you initially said that "AFR" is Air Fuel Ratio, I'd have known what "AFR" was and this part of my quoting you here wouldn't be as lengthy. I'd have just asked "what is correct 'AFR' for the car", lol.

Anyway, so I looked it up, and Torque Pro does have a way to monitor Air Fuel Ratio. I just have to go into the app and configure the parameters to make it happen. I'm also trying to figure out how to record live data with Torque Pro onto a *.CSV file so I can post it up here for everyone to analyze. Worst case scenario, I'll just post up screenshots like I did above.

XLR8 said:

1) Not really. There are ways you can get to it without removing the intake, but it's much more trouble than it's worth. There are creative ways that you can reach the sensor to turn it with a wrench, but it can be a nightmare to (a) reach the plug and squeeze the tab to disconnect, and (b) re-thread the sensor when you're done.

2) Yes, reinstall the sensors as normal before starting the car.

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The biggest problem I see with the rear primary is disconnecting - and later reconnecting - the pigtail part of it. That part I couldn't reach from under the car even if I tried.

I can get my o2 wrench on the o2 sensor no problem from underneath the car.

XLR8 said:

I can't help you with that. Ugh, CARB. Come to Texas. A WHOLE LOT of your neighbors are doing that. There are some surprisingly easy and inexpensive ways around your issue, but (a) they're just as illegal as buying non-CARB cats, and (b) they won't actually fix the problem (they'll just make the codes go away and stay away, but your car would still fail a tailpipe sniffer test).

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I know that. I have my reasons to stay, and the earliest I'd leave is looking like 5-7 years from now, so long as other external factors don't play a bigger role. I'm not looking at TX though. Based on what I'm seeing out there, sure everything else is cheap, but property taxes out there more than make up for the difference in cost of living. Cost of living will end up being the same. The state I'm looking at is actually North Carolina. It's way cheaper there than even TX. I could sell my house here in CA, use the profits from sale to buy a house the size I want out there in cash, and still have money left over. I can't say the same for TX.

Anyway, yes, I know MIL eliminators will work, but that won't fix my problem like you said. As for the sniffer test, the very first part of it here is a visual inspection by the smog tech to see if there are any signs of tampering with any of the emissions equipment. Adding MIL eliminators will definitely cause the car to fail right away. So will changing the CATs out for EPA certified units instead of CARB certified units.