"Offroad" Catalysts

[MTUH3]

I should have said, or lack there of...

So this has me thinking hypothetically here...

In the last week I have thrown 2 engine codes

1. P0296 - Post Catalyst O2 sensor Lean
2. P216A - Imbalance Air to Fuel Ratio

So far I have taken measures to resolve both codes by replacing the air filter (P0296) and cleaning the MAF Sensor (P216A).

We will see if the codes, or different ones return over the next week, but there is the possibility that the Catalysts are going bad and clogging. I could just replace the Catalysts, I could go with "high flow" catalysts, or upgrade to a combination of headers and catalysts or headers and no catalysts. (Clogging catalyst may be trapping more fuel particles, which may have thrown the P0296 and also affected the P216A as the ECU is assuming the A/F is off because it is not getting a good read on the O2 sensor.

I would prefer the last option, because of cost and no catalyst I would assume still flows better than a high flow catalyst.

Here is the trick: And this is where the post goes more into the Engine category.

1. I am in MI. No inspections.... yet... so I am clear there
2. I don't want to stare at a check engine light all the time. Can the flag be erased or fooled?
3. Even if I can fool the O2 sensors, the engine does still use that information to tune itself on the fly, what might be the impacts if I feed the ECU a dummy O2 reading vs an accurate one?
Corallary: Do the O2 sensors need the catalyst to function properly, or can they still perform their task without?

 

[JDUB]

 

[MTUH3]

I am starting to answer my own questions, it may not be so much that you need to get rid of the post catalyst O2 sensors. Sounds like the O2 sensors are looking for air to fuel ratios in the exhaust pipe, which the catalyst has no part of... it converts other compounds.

Or am I going off track?

 

[Phyguy]

Too complicated for me after a few Tecate's.

Dealer. Warranty. Fixed.

 

[MTUH3]

ha ha ha, that will probably be the route, but the easiest way to get a CAR approved in this house is to break something first

OK, getting closer, With the Power of Google.... I too can be an expert.

Kidding

There are usually two O2 sensors these days on the vehicles, one pre catalyst and on post. The Pre sensor is used to determine A/F ratio, the post O2 sensor is used to measure the "efficiency" of the catalyst. The Catalytic Converter can only do its job at high temperatures. If the temp in the system drops, it will force more fuel into the engine to raise the exhaust temperature in the catalyst, so it does its job better.

I assume from those that have put on after market headers, there is a place for the pre catalyst O2 sensor, in theory, the post O2 sensor could be replaced with a dummy function, and fool the ECU (telling the truck it is always operating at perfect temperature for a catalytic converter.

Well that is the theory anyway.

So here is where I am going with the two codes that have been thrown, and with a bit of a nudge from other posters.

It is likely, and I will monitor codes and performance over the next few weeks, that the catalytic converters are possibly becoming plugged (usually caused by too much unburned fuel getting through the engine). The post catalyst 02 sensor flagged a Lean Condition most likely because the Catalytic converter was collecting excess fuel particles (because it is plugged). The A/F Ratio imbalance code could be linked to the the post catalyst O2 sensor not picking up the right temps from the catalytic converter (either access heat from extra caused be trapped / excess fuel in the system causing it to flag a Rich Condition or that the the ECU was picking up on all the excess heat and leaned the engine out to compensate, throughing off the balance again)

 

[pirate air]

The up stream (before catalytic converter) oxygen sensor/s sole purpose is to provide data to the engine control module for fuel ratio corrections. The down stream (post catalytic converter) oxygen sensor/s sole purpose is to monitor the catalytic converter for proper operation. It has no part in correcting air fuel ratio. You could replace with high flow cats or no cats (off road use only of course....) and just turn off the rear oxygen sensor function via tune.

 

[Wilson]

I happen to have two high flow cats I took off my truck with sw headers lol. anyhow I would recommend looking into a diablosport tune.

 

[MTUH3]

The up stream (before catalytic converter) oxygen sensor/s sole purpose is to provide data to the engine control module for fuel ratio corrections. The down stream (post catalytic converter) oxygen sensor/s sole purpose is to monitor the catalytic converter for proper operation. It has no part in correcting air fuel ratio. You could replace with high flow cats or no cats (off road use only of course....) and just turn off the rear oxygen sensor function via tune.

Thanks Pirate... I was just reading up on that as you were posting. I have updated posts above with similar information.

The post can can affect A/F ratio based on Catalytic performance I understand, but agreed, a tune will correct the problem

 

[pirate air]

The post o2 will only affect fuel ratio in extreme conditions that most likely won't be seen in your typical daily driving. The up stream is constantly looking at changing fuel trims and sending data to calculate injector pulse width. The down stream is looking for steadiness, if the cat is functioning correctly, oxygen level stays consistent. Excessive fuel will plug the cats but its not the fuel that clogs the media, the excessive fuel over works the cat to the point it overheats and the media in side breaks apart and clogs the passage ways. At this point there's nothing you can do besides replace the cat/s. Cats can get hot enough to start your floor board on fire, I've watched it happen more than once.

 

[MTUH3]

Thanks Pirate, sounds exactly like what I have been reading. My suspicion in that with the Rallycrossing events and the on and off again of full throttle and the lack of speed to move enough air under the truck, the Cats just got over worked.

If I can save 200-300 bucks by going to offroad headers, I will swing it. May be weld in a 2nd **** to accommodate the 2nd O2 sensor, and if it throws codes, program it out.