Exhaust.... CATS

[mthomasOK]

Exhaust....

On a '97 4.0L OHV Explorer:
Does anybody understand the basic setup of the stock CAT system? It looks to me like it has from the exhaust manifold, sensors until it reaches the first CAT, then a sensor, then the next CAT, then another sensor then the muffler.... IS THIS TRUE? 2 Catalytic convertors???
I was in the process of ordering a new CAT when I noticed the (what looks like to me) double-CAT setup.... Help please!?!?

 

[Texplorer]

That is correct, the OHV's have two cats. One right after the other.

 

[mthomasOK]

yuck.... is that necessary? (I am personally a fan of the old style setups----ford 351 with open headers ) What can I do to simplify that setup?

 

[ChuckyD]

Please dont double post... it can get very confusing. I merged the 2

 

[yob_yeknom]

On '96 and later models equipped with OBD-II there should be an O2 sensor after the cats, even on the OHV engines.

With that in mind, there isn't anyway to 'simplify' that setup, or get rid of the cats or whatever you are thinking of doing. That O2 sensor after the cats reports back to the OBD-II system, telling if the cats are doing their jobs and reducing emissions or not. If you try to remove the cats, it will set off the check engine light and the engine will not run correctly.

 

[yob_yeknom]

In addition:

On pre '96 models (not sure on '91-92) there will be 2 O2 sensors and 2 cats. One sensor for each bank before the cats, then 2 cats one right after the other.

On '96 and later OHV engines, there are 3 O2 sensors and 2 cats. One sensor for each bank, then the 2 cats one after the other, but then another sensor after the cats.

On all SOHC engines, there a 4 O2 sensors and 2 cats. One sensor for each bank, then one cat for each bank, then another sensor after the cats for each bank.

 

[mthomasOK]

so no matter what, you have to have 2 cats on this system.... I was curious more than anything if I could knock it down to one.

 

[yob_yeknom]

Well, it's illegal to mess with your cats unless one is bad. But if you were to remove one, I doubt just the one left would reduce emissions enough to comply with what the OBD-II system expects.

Cats are pretty high flowing these days, so you don't have to worry about them being a major hinderence on the engine like on older vehicles. If you'd like to free up your exhaust, get a nice cat-back system. That will get rid of the restrictive (to be quiter) stock muffler. You'll get a little more (or a lot depending on which system you go with) noise and a lot more power with a better muffler.

 

[yob_yeknom]

Oh yeah, why were you looking to order a new cat anyways?

 

[Guy Groves]

I would suggest investing in other parts of your exhaust system - CAT back and headers, and a throttle body and maby a larger MAF, then there are chips. The CAT's are not the most restrictive component, I doubt you would notice any real improvement (seat of the pants, or on a dyno) by replacing them

If your vehicle has less than 50,000 They can not be altered, they are covered by Ford. If you have many miles on the vehicle or the converter(s) are physically damaged they can be replaced (under the law). The replacement aftermarket converter, in most cases, will be a single 3 way converter.

 

[mthomasOK]

The main reason for replacing my CAT is the nasty smell of rotten eggs coming from my exhaust. All my "new" car gurus all say the catalytic convertor is to blame. This (they say) makes sense because my CEL keeps coming on when I go uphill without accelerating, and let the engine pull itself up the hill. Hence, I am out on a mission to cure this problem.

 

[Guy Groves]

I am not familiar with the exact setup in your vehicle, but all you need to do is keep your O2 sensors and replace the CATs with an aftermarket unit. Most (not all) aftermarket CATs are three way and sized based upn the engine displacement. You should be able to get a single cat replacement from CarSound or Dynomax. CATCO also makes units, but most muffler shops I talked with stay away from the CATCO units.

The only thing you need to worry about is if the CAT is a Universal or OEM fit.

Universal fit units will have end pipes without flanges. The OEM fit unit should also include the mating flange.

If you get a Universal unit you can usually cut the necessary flange(s) off the existing CATs to use on the new setup. The big problem is Ford typically used an oval shaped pipe from the front flange into the first CAT. If you use a Universal CAT the flange will need to be modifid to go from the oval shape into a round pipe.
With a Universal unit the total length will be much shorter so you will have room to add the flange to the new CAT and add a little extra pipe to compensate for the length.

 

[mthomasOK]

GAS MILEAGE... CAN I IMPROVE?

I picked up some aftermarket replacements and have a welder friend of mine doing the replacement job.

Does anyone have an idea of how to improve mileage?

Ideas I was having was:
1) cold-air snorkel to force cold air down the air filter....
2) change plugs and wires
3) take off luggage rack (maybe)
4) possibly superchip...(will it improve mileage???)

Thanks guys for any input...

matt