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post #1 of 5 (permalink) Old 10-18-2006, 08:55 PM Thread Starter
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Question gas mileage

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
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post #2 of 5 (permalink) Old 10-19-2006, 05:15 AM
13s or broken
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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

1996-thunderbird Project 13's or broken
Mods now-PI intake, removed silencer, gutted third cat, flowmaster 40 series.17x9 03 cobra rims with 255/45/17s, lowered 2''
getting installed soon- 3.90 gears, aluminum carrier, Marauder tourqe converter, Jmod shift kit, Pi cams.
Coming soon mods- chip,Maf, tb and plenum,Ported and polished NPI heads, New exhaust, Kooks headers,massive weight reduction, And a dash of Nitrous.
And if the stock short block doesnt hold up then a nice built stroker modular.
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post #3 of 5 (permalink) Old 10-19-2006, 06:59 AM
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I read that earlier in one of the threads as well
removing cats isnt the best unless you get a tune or emil's
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post #4 of 5 (permalink) Old 10-19-2006, 10:50 PM
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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 can easily make the circuits to fool the EEC into thinking the rear O2s are working properly

Last edited by guitar maestro; 10-20-2006 at 07:28 PM.
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post #5 of 5 (permalink) Old 10-20-2006, 08:16 AM
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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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