Ford Oxygen Sensor Kills Catalytic

Ford Oxygen Sensor Kills Catalytic

Robo Tech was called to a shop with a 2004 Ford Fiesta, and a 1.4 liter Zetec engine. The vehicle had a code P0420, or Catalyst System Efficiency Below Threshold (Bank 1). The vehicle ran fine, with no apparent issues. So, the first thing the shop did was replace the front O2 sensor. They also replaced the air filter, and decided to throw in a full tune up while they were at it. Finally, they resorted to the infamous fuel injection cleaning to correct the problem. None of these remedies took care of the issue, and they finally gave up and decided to call me in for assistance.

The very first act that I did in tackling this problem was to do a graphing scan tool data stream analysis. I needed to graph the O2 sensors, to do a comparison of the signals. As a rule, the rear O2 sensor activity should be much lower than the front. As I proceeded to graph the signal, sure enough, the O2 sensor signals looked just right. The rear O2 sensor did have activity when I goosed the throttle, although much less. This was normal, so, I assumed that the issue was the converter.

Before I decided to go ahead and replace the converter, I decided to go a bit further, and do a fuel delivery analysis. The converter was an expensive proposition, and I wanted to be sure. So, I pulled up the fuel trims and fuel status. The fuel trims were at plus 4% and the fuel status was in closed loop. This was a perfect reading. The E C M was controlling the mixture. So, what else could I do to be 100% sure that the converter was faulty?

I finally decided to do a 5 gas analysis, using my gas analyzer unit. I knew that all engines are supposed to have about 0.5% Oxygen, and about 14% for the Carbon Dioxide, or C O 2. These 5-gas figures always point to a perfect combustion. As I did the 5-gas reading, low and behold, it was almost perfect. There's always a small amount of Carbon Monoxide in every mixture. After the converter it should be at about 0.5% as well, and I was seeing 0.9%, only slightly over. This converter was doing its job.

All converters need a swinging O2 sensor to operate. The front O2 sensor was definitely switching lean to reach, as it should. So, what was going on here? The rear O2 sensor had little activity, which is normal for a post O2 sensor!

But wait a minute? I suddenly remembered .... Get the whole story right here, right now!... See what happened next....

Presented using advanced software CG animation and editing technology to help you understand. Part of our Automotive Technology series shown here on this channel. Enjoy...

Category:

Autos & Vehicles

Tags:

• catalytic
• converter
• Ford
• Fiesta
• 1.4L
• O2
• O2 sensor
• auto
• automotive
• automotive technician
• car
• cars
• training
• school
• technology
• computer
• module
• current
• voltage
• electric
• electrical
• electronics
• wiring
• diagram
• educational
• commentary
• discussion
• analysis
• Ford Motor Company

[605manuel]

man i love your videos thanks for posting

[ADPTraining]

@605manuel Thank you... All we ask is that you participate and post away. Don't forget the like button, but only if you enjoy the videos. Also, stay tuned for free stuff. Subscribe now!...

[xxioryyagamixx]

do you have a graph on how the rear O2 sensor should work????

am interested on seeing it

[ADPTraining]

@xxioryyagamixx I suggest you look up the O2 sensor videos on this channel. they cover everything you need to know. Let me know if you have more questions afterwards... Thanks for posting...

PS. There is a way to detect a faulty BABY converter, but it's not easy. We developed this technique a few years back. Maybe I'll post more on the matter later...

[TRcustomengineering]

@ADPTraining Cool.

Thanks for taking the time to reply.

I'm not to up to date on newer emission systems so i appreciate it.

[ADPTraining]

@TRcustomengineering Most HC traps are on Diesels, since Diesels operate at general cooler temps. But, HC traps are also found on gas vehicles as well, most on baby converter vehicles. These baby cats are now almost used exclusively. The newer vehicles have dual-baby-cats right at the exhaust and dual front O2 sensors. The cats are replaced by unbolting a 3 bolt flange. Very easy to replace. The idea is the closer to the exhaust, the less converter honeycomb material needed. Thanks for posting.

[TRcustomengineering]

@ADPTraining Ok, Thanks for explaning.

I looked up a HC trap and it looks like there just on Diesel vehicles, Is this true?

Thanks again

[ADPTraining]

@TRcustomengineering Yes, let me explain. I know what you're referring to. That wasn't a catalytic converter. It's called an HC trap. These are found after the baby cats, but under the vehicle. They look like regular old fashioned converters. They operate in a different way. All they do is absorb the unburned fuel (HC) during rich operation and then release and burn the HCs when the engine runs normal or leaner. HC traps can get clogged and rendered useless if the mix runs rich for too long.

[TRcustomengineering]

Well done.

I've seen small catalytic converters like that before on some vehicles.

Do any cars have two catalytic converters? Cause one time i saw something that looked like a baby catalytic converters and then a normal looking one.

I believe it was on a Audi but it was a while ago so i don't remember 100%.

[ADPTraining]

@gratefuldead42022 Robo-Tech girl keeps asking me for a chance, like in Auto-Tech Consumer Reports. I don't know what to say... Thanks for posting...