I have a 01 F-150 S-CREW that I had a custom exhaust put on. The OEM exhaust was totally taken out including the cats. All was replaced with 2.5 piping into 2 flowmaster 40's then out infront of right rear tire. Since I have done this my gas milage has gone to hell, my shifting is messed up, can be in 4th gear by 28 mph, and on the highway it is constantly kicking down into passing gear on the smallest hills. I disconnected the battery to reset the system hoping this would help but it hasnt. Any tech help or advise would be greatly appreciated.

P.S. I still have the cats, should I weld them back on and if so does anyone have a picture so I can weld them together correctly since all 4 were cut off seperatly

 

Isn't it federally mandated that you have to have cats? Now you got a loud attention grabbing truck that a trooper is gonna notice - not cool. weld them back on to stock and buy a cat - back.

 

Yes it is mandated, but it helps to live where I dont have to do any kind of emissions checks and its also a plus when you are in law enforcement and know loop holes

 

ur loosing alot of back pressure with equals back pressure which exquals compression.. so yes ur truck will run bad without cats on it

 

I have a simular setup but i have a x pipe installed. After removing the cats if you did'nt get a tune or mil for it will run real rich = bad gas mileage. after doing my exhaust and tune i picked up a little bottom end and alot of mid range

SVTWIZARD (Ray)

((((YGROWUP)))
If it has Tit's or tires it will cause problems!

 

There are no loopholes for breaking the law.
Back pressure BS again eh Faster? Some restriction is needed for proper scavenging but you would be surprised how little you can get away with. Sam Memolo on 2 guys garage actually connected a pressure meter to an F150 and showed that the stock exhaust has very little back pressure. Mike Troyer also stated that the factory cats have very good flow unlike the cats of the old days.
Did you put your O2 sensors back on? The two closest to the exhaust manifold are need to control Air:Fuel ratio. The outer 2 are just for the CEL and can be replaced with a resistor.

 

Yes I did put the O2 sensors back in but with sims attached. The other 2 are not present on my truck from the factory. As far as backpressure goes I did lose alot of low end but my mid-range is killer. But whay the extreme shifting problems?

 

Take off the sims and see if your A:F ratio gets better. I have a 2001 with a 5.4L and there are 4 O2 sensors, are you sure you only had 2? What engine? The rear 2 can be sim'ed out as they are only for emmisions and check engine light but the front 2 are needed for correct engine performance.

 

I have th 4.6L engine.

 

Can't you just tap the pipes and reinstall all of the O2s?

 

That is what we had to do since Ford sims have to be put between the O2 and the wiring harness where the 2 connect

 

Take the sims out and see how it runs.

 

ford cats usually have about 1-2PSI of back pressure any more and ur cats are clogged any less and u will likely throw a CEL

 

I'm sorry if some one take me for a smart *** but do you all know what complexity you entered into by removing the OX sensors?
It is really deep and may not be worth while to do much explaining unless you want to know..
Just a few tidbits.
1. No Ox sensors makes the PCM go to fixed internal fuel tables that are very rich to protect the engine. That translates to really poor fuel milage.
2. The PCM looks at the rear sensors and does a compare to the front sensors as a way to access the condition of the cats. No cats equals total failure of that function and a cel/code report THAT YOU CANNOT get away from with any simple bypass method.
3. The stock system is tuned for the best overall average torque for the averge owner so it's not at all surprising low end is lost when other systems are installed..
And theres a lot more to it folks.
Your playing with a complex total system and thinking it's too simple.

 

How did your truck only come with 2 O2 sensors? There should be 4...

Maybe you could put some high flow cats in there rather than no cats.