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i have a 95 4.6 and after i my two main cats cut off my gas mileage went down quite abit can does anyone have a reason for this.


only mods done is a k and n panel filter true duel exhaust and air silancer
removed
thanks
 

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some one mentioned before if you cut off the main cats the computer goes into 'limp home' mode , but i dont know for sure
 

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edit: after re-reading some stuff, its true what nick says in the next post; it really shouldnt affect it if any at all....you can easily make the circuits to fool the EEC into thinking the rear O2s are working properly


http://members.tccoa.com/tinman/MIL/index.html
 

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Actually when they cut the cats there is probably an exhaust leak making the front O2 read lean which is skewing what the computer is expecting to see. You need to check your fuel trims to see if they are all over the place.

The stock Ford program actually is slightly rich as that lowers NOx and then the cats convert the excess HC.

The rear O2 only look to see that the cats are working, if not the PCM throws a bad cat code but that doesn't change the performance of the car. You just get to drive with a check engine light all the time. You can make a simple electrical circuit for the rear O2 sensors with a single resistor and cap to each sensor that will fool the computer into thinking the cats are still there, costs about $3 for the parts at Radio Shack.
 
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