Bought the wife a 99 Expedition, and have some questions on the exhaust system. I know about the O2 sensors that are just downstream of the exhaust manifolds, but there is a sensor downstream of the cats, where the y connection is. What is its purpose? The cats will soon be replaced with straight 2 1/4 pipe, then Y into 3" back through an aftermarket muffler. What affect will this have on the mystery sensor? I can deal with a service engine light, but if the computer has any other reactions, I will have to figure out how to fool it, I guess. Is this the dreaded OBD II I have heard about? Is this on 49 state vehicles or just California emissions vehicles? (My Expedition is originally a California vehicle)

Thanks in advance!!!

 

I am rather new to the exhaust of Expi's but I think that I may have read somewhere that they have approx four O2 sensors. Two on each side of the engine on the exhaust. Is it possible that you are referring to the other O2 sensor or sensors? Just a thought. Good luck.

Jakegypsum // Ford fleet, soup to nuts.

 

The sensor after the converters is for monitoring cat efficiency. So if you no longer have any cats it won't work and will set a check engine light that you won't be able to get rid of. I think that cat removeable is illegal all states. Anyone? Fuel trim may be effected by removing the cats, not sure thou. If so it would effect how the engine runs all the time.


2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

 

Removing cats is illegal in the U.S.. There is a federal law that states it is illegal to alter or remove emissions components from a vehicle. There are 4 cats on the expedition. 2 of them lower hydocarbons and carbon monoxide. The other 2 lower oxides of nitrogen. Catalyst effectively burn emmisions and in effect turn them into H2O and O2. Removing the cats will definantely turn on a check engine light because the downstream O2s are sensing a difference in O2. In thoery it should not change the air/fuel mixture or anything like that, but don't quote me on that. Im sure there is a way to trick the computer into thinking that everything is fine and dandy back there but I'm not going to put any thought to it because there is no reason to remove cats unless you are building a very radical engine. Most Catalytic converters on modern vehicles offer very little restriction. Don't be afraid of OBD2. As long as you keep your engine running properly you should not have any problems.

 

Thanks for the response; I am definitely not building a radical engine in this application, but I have never had a vehicle with catalytic converters and don't see any reason to start now. I have removed them primarily due to their restriction and its effect on performance and efficiency, and because of the high heat created by the cat and the possibility of starting an under-vehicle fire (if driving/parking on dry grass/ stubble fields). Frankly- and I hope I don't offend anyone- I don't care about the federal emissions rules and their penalties; I guess I will when someone starts crawling under my vehicles and checking, but until then... I keep my vehicles in a top state of tune and do a very thorough job of maintenance, and I don't believe they are a factor in air quality. As long as we allow visibly polluting vehicles from other countries (i.e. our southern border) to travel our roads, the feds can't be taking this issue seriously.
If someone can show verifiable evidence that the backpressure is negligible, or that the check engine condition will cause drivability/performance issues, then I may consider additional heat shielding and forgo the straight pipes.

Not a Cat Fan

 

Anyone know if these after cat sensors will screw up the state of tune with the cats gone? Any way to fool or bypass these sensors?
Appreciate any help or ideas-
Thanks.

 

I believe the easiest way to bypass the O2 Sensor is to floor the gas pedal. My understanding is that a wide open throttle condition bypasses the emissions components in the truck. Assuming this is true, there is absolutely no reason I can think of to disable an O2 sensor. The sensor is only operational while cruising, in which case it allows the computer to lean out the fuel ratio and increase economy. It is also a great sensor to identify engine problems.

I also have been told by numerous sources that modern catalytic converters are relatively free flowing, unlike the ones of years gone by. I looked into getting a high flow cat but decided it wasn't worth the expense and hassle. I see no reason to mess with the stock equipment.

Jerm

 

>Thanks for the response; I am definitely not building a
>radical engine in this application, but I have never had a
>vehicle with catalytic converters and don't see any reason
>to start now. I have removed them primarily due to their
>restriction and its effect on performance and efficiency,
>and because of the high heat created by the cat and the
>possibility of starting an under-vehicle fire (if
>driving/parking on dry grass/ stubble fields). Frankly- and
>I hope I don't offend anyone- I don't care about the federal
>emissions rules and their penalties; I guess I will when
>someone starts crawling under my vehicles and checking, but
>until then... I keep my vehicles in a top state of tune and
>do a very thorough job of maintenance, and I don't believe
>they are a factor in air quality. As long as we allow
>visibly polluting vehicles from other countries (i.e. our
>southern border) to travel our roads, the feds can't be
>taking this issue seriously.
>If someone can show verifiable evidence that the
>backpressure is negligible, or that the check engine
>condition will cause drivability/performance issues, then I
>may consider additional heat shielding and forgo the
>straight pipes.
>
> Not a Cat Fan


Well, I WAS of the same though as you with regard to the cat converters. Prior to owning the Exy, I had an Audi A4. I had done a custom exhaust from the cat back (there were 4 mufflers on the thing!). After about a year, one of my cats went out. I talked to Audi and if one goes, you have to replace them both. $ 2,700 with the down pipes PER ENGINE BANK! PLUS LABOR!!!!!

Well, I went down to my local muffler shop and finally convienced them I was not a cop and to cut the things out. So it was done, and did I regret it. IT IS LOUD!!! REALLY LOUD!!!!!! I did not have any baffles put in the pipes to cut the noise. There was no performance increase to be had at all (by cutting the cats).

I even had a few new problem pop up. FUMES. The car always smelled of exhaust. I (as a man who loves the smell) did not mind, however, the ladies did not think as highly as I did of it. As well, after about 2 years, I had to replace the entitre exhaust system again. Becuase of the fumes, it ate where the pipe comes into my muffler (and that did nothing for the sound that was already there).

When I replaced my exhaust the last time, I added the baffles, and added something else (which I had no idea existed). There are now available performance cat converts. They still reduce the emissions, but still give better performance. I placed them on the car and it was so sweet. It still had a very different exhaust note, but no more smell and it actually increased performance on the vehicle.

I had done some testing with the G-Meter (as it was a quatro, I could not dyno it). I had all of the slips in the car to give exacts, but they stayed in the car when it went. I do not have specificsany more, but trust me it WAS faster with the performance cats on.

I am glad I made the decision to add the cats for one last reason. Here in TX, the do have emmisions tests in certin counties. They actually stick a tube in the pipe and measure the emissions. If they are too high, the vehicle will not pass, and you cannot drive. Well, I lived in a county that was just outside the county that tested. This year (6 months after I got the Exy), they passed a new law that ALL VEHICLES IN ALL COUNTIES MUST BE TESTED.

I am not stupid enough to think that there are not ways around the system, but things are a lot easier when you go by the books.

I am not a tree hugger, but a performance finder. I too thought it would help. But with careful trial and error, I found out the truth.

Just my 2 cents.