The only reason to remove the rear cats is to change the tone/volume of the exhaust note, it's not gonna hurt performance that much at all.

And yes it is illegal to remove emissions equipment without replacing them, a federal law covers that, so if you have emission testing in your state don't bother touching the cats.

Another option is installing high flow cats, there are many manufactures that make them for many different cars but they are a little expensive.

On most cars made in the past 10 years there are 4 cats, and 4 o2 sensors. The sensors are before and after the first cat, the rear ones aren't even monitered, so the computer won't even know that they are there in the first place.


As far as that stupid little flebay "performance chip"... I'm surprised they sell any at all, are people really that stupid to think that they will get that much power and mileage increase from such a cheap little thing?

 

if the 94 doesn't have the rear oxygen sensors, the cats are only there for emission out and the engine doesn't care. If there are oxygen sensors after the cats, the engine will very much care about removing them. I think al already state this, but just to make sure... here it is again.

Eddie is right about the chip (resistor) as I stated early on in this thread. It doesn't work. Even if it is a chip generating a one-wire PWM signal, it will be overcome by the engine computer one way or another. Most likely it will simply ignore the bad sensor data and run less efficiently.

For pipe size, we were talking more about post muffler tail pipe flare (for looks I think) that may add some volume by working like a megaphone (re: pep squads?) or this may just seem that way since it allows the sound to spread out more. I've stated that I don't know much about this and it's mostly speculation on my part about tone and volume.

If you want to hear what my car sounds like... check my vid on youtube. It was recorded with the y pipe and single exhaust, but the only difference in sound between that and the current dual setup is the volume (it's about time and a half as loud now). I have gotten better gas mileage out of it though. I originally got the car and was getting about 11.5mpg in town. I now get around 14mpg in town. Highway was about 17 when I got the car. Now it's about 21.5. I have to add that I did change the gearing in my transmission to a wide range gear set and added a redneck intake with a K&N Apollo as the filter. You can check out the intake in this post. My car gets off the line better than the 93 vic we have (stll pure stock), but the vic will pull harder in the mid and upper RPM range due to that 4.6 engine that's in it. The old 302 will lift the nose and go much harder than the 93 (I think this is mainly due to the differences between speed density and MAF systems - MAF has a slight lag due to the flow sensor waiting for air to move and the computer taking a few more cycles to computer the fuel mix while the speed density just checks a table and doesn't really calculate anything.)

If I had the means and time needed to put a 351 cam in and swap out for a mark 7 ECC, get heads and upper intake plenum from an HO engine, and all that like some folks have done, then I'd probably have even better gas mileage... when I drive normal instead of like a bat outta hell that is. I've still managed a few 11.5 mpg tanks but that was due to driving like a bonehead.

I actually didn't know about the federal law (since I know quite a few folks that have their vehicles registered in non-emission controlled areas and no emission equipment on their cars the thought never crossed my mind).

 

[quote=merky_marquis;12947]On most cars made in the past 10 years there are 4 cats, and 4 o2 sensors. The sensors are before and after the first cat, the rear ones aren't even monitered, so the computer won't even know that they are there in the first place.
quote]


Yes,those are monitored by the pcm. Ironically the 02 sensors in the rear (behind cats) are called cat monitors. (don't ask my parts guy for a rear 02 sensor!).
They are actually the same physical sensor as the front,just does a different job and has a different plug (GM's use interchangeable plugs generally).

The job of the rear 02 sensor is to judge whether the cats are still efficiently cleaning the exhaust.
The rear 02 sensors have the same codes as the front,the only difference being they are referred to as sensor 2 (HO2S12 and HO2S22).
They also have two extra codes,one for each bank cat-P0420 and P0430.
These are cat efficiency codes,and basically mean your cats are no longer cleaning the exhaust enough.

The four cats aren't needed though honestly.
Cats at the dealer are expensive,and some people I send to the local muffler shop owned by a buddy.
He cuts off the rear cat,guts the front (light off cat) and installs a new one in the rear.
Works everytime,the front light off cat is only needed for cold start up I believe to take the place of the old secondary air system that injected cold air on startup into the exhaust till the cats get hot enough.

Here is a link to a writeup I did,it is direct from the Ford driveability training class.
Hope it helps someone out.

Bottom of page
http://www.monodax.com/forums/off-to...operation.html

Here's a quote from another writeup I did on OBDII monitors
10. Catalyst Monitor:The catalyst monitor reads the upstream (A) and downstream (B) HO2S switches and compares them to each other to determine catalyst efficiency.
For this example, an upstream reading of 125 and a downstream reading of 7 gives a catalyst efficiency of 7/125 = 0.056.

( http://www.monodax.com/forums/off-to...tors-info.html )

 

You won't spend less than $240-250 on a performance chip from an established company unless you can find some place that stocked up on the part you need and is having a fire-sale.

 

if you want to get into serious money and get a bit more power try rpmoutlet.com and look up 99-04 mustang parts and lookup the PI (power improvement) heads.

 

You want chips !?? Get a bag of FRITOS !!

Those 70-dollar so-called "chips" are a total and complete fraud !!
I bought one that had a money-back guarantee -- and gave it a thorough testing by driving about 2,000 miles with an Actron Code Scanner attached to the OBD II port.
Recording the fuel mileage to two (2) decimal places, and the time-to-distance by the nearest 15 minutes and one-tength of a mile.
There was absolutely NO improvement of any kind over the "stock" ignition (OEM coils, Bosch 9605 Iridium plugs, Bosch Mag-Core Ignition wires).
Not satisfied with the test results, I pried the housing open, only to find a cheap resistor inside.
NO CHIP or circuitry of any kind !!
I sent it back and got a full refund.

Let's face it -- a Grand Marquis never was and never will be a hot rod or a sports car.
The most bang-for-the-buck will come from installing a 2" dual exhaust.
I used a Walker H-Pipe, with 2" MagnaFlow (part #18134) Glasspacks and Walker tailpipes.
The Walker-MagnaFlow combo yielded 22 hp on my '95 resto, tested with a G-Tech Pro.

 

Forget those "chips" -- if you're hungry, get a bag of Cheetos !!
You're not gonna get a 2-ton car to be very fast off the line or in the quarter-mile.
Here's what I did to make my '95 Merc restoration go faster:
1.- Dual exhausts : Walker H-Pipe; Magnaflow 2" glasspacs, Walker tailpipes.
2.- K&N air filter using STOCK air box with snorkel removed- air is ducted from forward of the engine compartment through flexible aluminum clothes dryer pipe.
3.- Mallory adjustable fuel pressure regulator - 35 psi @ warm idle, with vacuum hoses connected and all accessories OFF.
4.- Bosch Double Iridium plugs @ .052
5.- B&M Shift Improver Kit.
Quarter-mile = 16.2 @ 87 mph
I got the parts at Amazon.com and did all the work myself, with the exhaust welded up by "MufflerMasters", Avondale, AZ.
I'm 78 years old, and STILL can't believe that young people believe that you can stuff 10 pounds of poop into a 5-lb bag !!