I've got a 01 supercrew with the 5.4 and about 150'000 miles. Last year the truck started misfiring and shacking at times so I replaced the plugs and coil packs. Now the truck is just weak and the gas milage is averaging around 11 mpg. I'm running the k&n filter stock type but no other upgrades. Could someone give me some ideas why the power loss and mpg loss.

Thanks
Hypergt

 

What kind of plugs did you get?

 

well with the mileage i would start by upgrading your exhaust system cause i can about gaurantee that your catalytic converters are more than likely shot. than can really kill your power output and destroy your gas mileage. just do your baiscs first. since you've replaced your plugs:- clean your K&N filter, replace your fuel filter, you may wanna try to decarb the engine as well with either seafoam or a good water/auto tranny fluid mix. you'd be surprised how much it can help. you probably wanna to clean the throttle body of all the carbon as well. try this first and see what happens

(if you have never decarb'ed your engine before talk to someone that has or take it to a shop that will do it. you can easily overload the engine and end up hydrolocking it, then you'll be in the market for a new engine)

 

Don't overlook the 02 sensors especially for better mpg

 

^ what he said

 

you need to do a few things. clean the filter on your intake and re oil it. flush your differential fluid and tranny fluid. if you have a little money to spend on the truck put a new muffler on (i recommend magnaflow) and get 3" piping. you have a lot of miles on your original cats so get new ones put on. you might as well spend the extra 20 bucks and get high flows on the 2 rear.

 

where's do you buy the new CATS at ?

 

the exhaust will have them and if not you can go to your local dealership and have a set ordered.. since your truck is common now they'll more than likely have them..the 3" exhaust in my opinion is a little overkill 2 1/2 should be enough.. just my .02

 

if ur doing a SI SO muffler u should do 3". better flow. if your doing SI DO you do 3" in 2.25" out. true duals 2.25". if u dont live in a state where smog is in issue...u should do high flow cats..little more expensive but welllll worth it. if u live in a state like i do in cali where u need smog every 2 years ull need cats that are DOT approved, or say CARB on them. u can order cats on ebay..muuuch cheaper than through the dealerships.

 

i put ams-oil in my truck and noticed the power difference right away, and gained nice boost in gas mileage.