Upon the suggestion of many here a little while ago I did my first 'tune-up'. My truck was over 105,000miles and I was still sporting the original facotry plugs, wires, fuel filter, etc. After my tuneup everything seemed about the same, might idle a little smoother, but my first full tank of gas has revealed the worse mpg I think I have ever got. My dialy grind in the city is about 40/60 city/hwy and I typically have been getting mid-14's. After tuneup I got 13.2mpg. About a 1mpg drop, not extreme but enough that I wanted to vent I guess. I'll have to see how the next couple tanks average out.

Here is what I did. First I went to valvoline instant oil change because I dislike doing that myself in the winter and they were running a special. Got the 4x4 service done, both axles, transmission, tcase, and motor oil. I then swapped the plugs and wires with new motorcraft ones. The original plugs had no platinum left on em and were averaging .07-.08 gap. I gapped the new ones at about .052 and I used bulb grease on the plug wires. Also swapped fuel filter. Air filter is a k&n and was fine.

I was really looking forward to maybe an increase in mpg but instead I got a decrease. I havent yet got a chance to take it on a highway trip.

 

it is probably just the ambient temp that has effected the milage, but the wieght of the oil can effect drag between the gears and bearings. should be 5w20 or 30 in the motor. axles should be synthetic in the back, and dont hurt in the front. assume the transmission is MERCON V-- they cant hardly screw that up. measure a couple more tanks to get a good average.

 

Maybe unhook the battery to reset the computer so it can adapt to the new parts? Or it will eventually do it itself over time. This time of year is hard on gas mileage since most of us warm up our vehicles and such.

 

Well hopefulyy it will improve some, but the temp this past tank of gas hasnt been much different than the last 2 months. It even was near record high a little bit ago so if anything I should have got better milleage. I put synthetic in both axles, cant remember what the xfer case was, and its a stick so I am guessing when they said tranny they were talking about clutch fluid. I usually always use the same oil, 5w30. I wasnt thinking that those things would require a computer reset or anything? Anyhow, I'll give it another tank or two but I can already tell this tank is going by quicker too. arghhh! lol

 

DId they list the fluids, by type that they put in? Just curious. I know the Manual trans in my 97 calls for ATF.