I went for a ride today and put abought 150 miles on the truck and when I got home and came to a stop it seemed like the truck was running a little off. I dont know how to describe it other than it sounded funny and idled a little ruff. The truck ran fine down the road at speed and seemed to be getting better than normal milage. The only thing I noticed was it seemed to take a lot longer to build boost a few times taking off from stop lights. The milage for the trip started out normal around 17 at 60 mph. It sat there for abought 60 miles then with in a few miles it droped to around 16 with no change in speed or hills or any thing. On the way home it started dropping into the 15s so I reset the overhead abought 50 miles from home and when I shut it off in the driveway it was reading 18.3, an all time high. Does this sound familiar to anyone? Any ideas what would cause it to run ruff all of a sudden? I stoped to get a soda abought 40 miles from home and it was idleing normal then with the overhead reading arounf 17. It was abought 1/2 way home from there that the overhead went up abought 1 mpg. Any ideas at all?

 

Possible water in the fuel? Did you buy that last load of fuel from somewhere new? May want to do a precautionary drain of the fuel bowl to remove any possible water in there.

Once you start resetting the overhead computer, all bets are off on doing any short term comparisons.

 

Thanks I will drain the water seperator. I did get my last tank of fuel at a new location but it was a large Shell truck stop so I figured it was safe. Abought an hour after I posted this we left again and when I restarted it it ran perfectly smooth again. This 600 is a quirky motor.

 

The overhead mileage is there pretty much for entertainment value. Too many variables that can make it change 1-2 mpg for any diagnostic value.

 

Ya I realize its not always acurate. I just have never seen it that high before. I have checked it many times and for the most part its usaly real close, but it has also been off by a few mpg. I was mostly concerned with the ruff idle as I have never seen it do this before. I have just short of 10000 miles on it now and thats a new quark to add to the list of odd things this truck does. I was wondering if it is a telltale sign of things to come like the white smoke at shift points or something.