Ok so it warmed up into the 20's today so I was able to take a look at my truck. I was able to locate the MAP sensor between the intake manifold and the distributed. It looks like an easy fix. I'm gonna change the o2 sensor and that MAP sensor this week and see what happens. Also I bought those fancy Bosch platinum spark plugs with a lifetime warranty so I'm gonna swap those out cause they are covered with grime. I just changed the thermostat about a month ago but the housing is cracked so I need to get a new one of those... There are 2 vaccume lines coming out of the front of the intake manifold that are plugged with screws, I don't know where they go though... I also need to buy that oval to round rubber thing that goes from the air filter to the left side of the engine compartment but I don't know what its called... I also bought a performance chip on e bay for 10 bucks hopefully that will help my fuel economy... I'm not sure what a cataletic converter even looks like but I know when I got my truck smogged he put n/a next to cataletic converter, but I did pay him to pass it so I don't know if I do have one or not. Are there any other sensors I should change that I don't know about? I changed the temp sensor but that's about it...
Ok when you plan to change the thermosat make sure you get one that rated for 192-195 degress F verison this is the only way you can get it back in line with computer controller.
For the performace chip that is kinda like touch and go item some case it can improve the fuel ecomeny or increase power but few case it will do both at once ( by altering the fuel curve and timming curve )
For the catyatic converter that useally located before the main muffer useally about a meter ( 3 feet ) behind the engine. most 454 useally use large single catyatic converter but there are few case it may have dual CC's most the 5.7's useally have single CC's you can tell where it was by a short peice of pipe which it was filled in by the pipe clamp or welded marks either way and btw the length useally half meter long ( about 18 inches ) for standard size but for 7.4's it will be 3/4 meter long unless it was plummed for dual exhaust.
There should be one vaccum line that go to the fuel canster which it will be located left front area I think below the head light if my memory serve me right ( My diesel verison do not have the fuel canster at all ) the other one I don't really recall without looking up the service manual book otherwise follow the hood sticker it will show the diagram I know the diagram will show for 7.4 L verison but the 5.7 L verison it should be simauair. so hook it up like that.
I am pretty sure the MAP and O2 sensor is out of wack that why you are using more fuel it should be for your engine.
Check your engine oil and smell for gaz if alot of gaz in there change the engine lube oil ( they can ruin the bearings )
What kind of fuel milage you are getting a rough estame ? I know the 7.4L never get over 10 MPG hiway the 5.7 should hit about 12 to 14 MPG range. but if you are useing " winter " gas the milage will drop some.
You may have to buy a OB scanner to read the computer to see what is going on on tempture and O2 reading and MAP reading and cross refered to the service manual for correct setting for each model ( both 5.7 et 7.4's )