bb400guy

Okay, so I bought a 2005 FX4 5.4L as in my sig. Only problem is the guy who owned it before me may have screwed up the exhaust. Here is what it has. Airaid intake, some kind of cheap shorty headers (they were crack so I removed them, not fun!) turn off or mil eliminators for O2 sensors (I think that's how u say it), he also hollowed out that cats, then put in true dual 14" Dyno Flow mufflers. He also had the truck tuned, but most likely did the exhaust after it was tuned. Basically, the truck has lost some low end torque and gets bad city gas mileage (10MPG driven very easy). Highway mileage probably is any better but I don't know that as it's so darn loud I can't drive any more than 45 mins without getting a headache. So, hear is what I am planning on doing:
1.) Put back on the stock manifolds as they are in good shape. This should get some low end torque back.
2.) Put on some hi-flow cats, reinstall O2 sensors
3.) Put Y pipe back in
4.) Choose a SI/DO muffler (help here) that has a low deep rumble in the city but is quiet on the highway.
5.) then go get the truck retuned

I am redoing the exhaust with a few things in mind. My truck is city stop and go driven Mon-Fri, then highway driven on the weekends. I only pull an ATV / boat, max 3000 lbs towing and will only be at 70MPH max. so power in the 3500+ rpm band is a non factor for me. As good as MPG as I can get 14-16 city / 17-19 highway (hoping for anyways).

Any thoughts or am I way off base.

JohnD

The numbers youa re hoping for are reasonabdle with those changes. However, if the only time you are on the highway you are towing then do not expect 17-19. For a muffler that sounds good without being obnoxious, go with a magnaflow. Flowmaster has a big following, however, they can create a lot of interior drone. Ive never heard one magnaflow owner ever complain about drone, myself included. Good luck getting the truck back in shape. Unless you got a really good deal on the truck, why would you buy one in that shape?

Siragalos

I have Flowmaster Force II on my truck, and it sounds great, its quite while its running, loud when you floor it.

bb400guy

I'm new to "newer" trucks, the last one I owned was a 1981 Dodge slant six with over 900,000KM! Damn good truck for its day. Could fix it with bubble gum and duct tape. Well the guy who sold it to me went over what he did, and claimed 15MPG city, 19MPG highway and me being new I bought it hook line any sinker. Oh well. The only thing I didn't like about it when I bought it was the noise level, but I figured a simple muffler swap would solve that issue. Then I drove it for 2 months and hand calc'd the mileage and was less than impressed. Paid $16K for the truck and it came with a new box cover. Very nice shape body/interiorwise. Most F150s go for around $18K-$19K and aren't nearly as nice looking. Hopefully I'll get back some MPG.

bb400guy

I put on the stock manifolds and took the truck to the muffler shop. They put on two high flow cats, kept the true dual set up as recommended by them, but they installed an x-pipe right after the cats, then put on two longer Flo Pro Max SS mufflers (basically a Magnaflow copy), and got rid of the stock Ford muffler mounts, and replaced them with hangers. Results, the truck sounds good, give it some gas and a nice deeper tone, reach a level RPM and it's nice a quiet with no drone at all, even at highway speed. Also gained some low end back. A nice surprize (pay attention for anyone having cab/seat vibration issues) was the new hangers. Once warm and at idle around 500 RPM, if the truck was in park or neutral, the truck had quite a bit of interior cab/seat vibration, I could see the passenger seat head rest shaking! The new rubber hangers better isolated the exhaust, and no vibration! Apparently the stock exhaust mounts are garbage.

One last question. I'm going to get the tune adjusted for the O2 sensors and re-checked by the same company that did it to begin with. They want $350! To me that sounds pretty high just to turn on the O2 sensors. The shop said there is a lot more involved then just turing on the O2 sensors. Since no parts are needed this is all labor, even at $75/hr, this shouldn't take 4.5 hours! Am I wrong or is this more or less the going rate?