Fuel Managment.. NEED HELP!!!!!

[Hbear1027]

I have had my Truck for about 4 yrs.. the first 2 yrs i had it i got like 400 miles to a tank.. now i get 260 mile to a tank.. i would like a good run down list of everything that could be wrong with it.. i have replaced so many parts and done so much and i cant figure it out..If anyone has had this problem or knows what to do let me know...

[OverBoardProject]

Have you done a compression test? If it's good then a good tune up, new air filter, plugs, and what not. Check the plug gap... it's so often over looked.

I saw an article in Hot Rod mag a few years ago, about spark plug gap, vs fuel milage, vs power that would probably intrest everyone. I'll try and find it, and post it here soon.

[Hbear1027]

have done a turn up on it.. um i pretty much change the Air filter, plugs and wires every 3,000 miles when i do my oil.. i had to change the cat and a week later the problem started do you think the cat might be the problems..

[busa_4]

if you changed your cats you are going to want to reset the ecm memory. pull the ecm fuse/relay for ~5-10 minutes. that will clear all the memory in the computer. your vehicle will run crappy for a few minutes until it can relearn all the sensor values. i would recommend changing all the o2 sensors. over time there not as efficient causing fuel mileage loss. a compression test will tell you if your engine is mechanically sound. low compression will cause poor fuel economy. i would check the fuel system. i am assuming this vehicle has the vortex motor with the spider injection system. check the valve for leakage. if it is leaking, it will cause a rich condition. check all that and get back to us.

[Mikado14]

You change plugs and wires every 3,000mi.???????