OK guys the 99 fuel economy dropped from 20 to 12-14mpg. engine runs normal i cleaned IATS and map no diff . i can hooked an ohms meter to the IATS and blow hot air on it and it changes the ohms reading (lower) no codes good fuel pressure any ideas?

 

You may have gotten a real load of winter mix with #1 diesel or kerosene mixture. Try a different fuel supplier on next fillup.

 

no winter fuel hear + all the other truck get fuel from the same supplier and havent lost MPGs.next

 

mine started that then the cps went out simple replacement and the milage is back up there

 

cps? is that the crank shaft sensor

 

yes, cps stands for crank position sensor. it could be malfunctioning enough to affect the mileage but not enough to throw a code out. Also note that there is a position sensor in the VP 44 pump, usually with the VP series pumps the cps can die and the engine will run but take more cranking to start because the sensor in the pump is spinning half the speed if the crank (same as cam). But if this sensor goes...caput your dead in water.

 

well it barely turn over and it starts so i have a hard time thinking its the cps but could be. hate to have to change it with the vp on any thing else do it?

 

Is the torque converter clutch engaging and staying engaged?

 

rebal, let us know how and what you find out, It looks like I have the same problem.

 

me too, no other indication.

 

With fuel past $4/gal. we might need to look at locking fuel tank caps.

 

Just saw a story on the local news about fuel theft becoming a real problem. They said though that most commonly the crooks don't siphon, they poke a hole in the bottom of the tank and drain from there. Just something else to worry about!

 

My fuel mileage dropped way down and then I started getting fault codes for over boost. I replaced the waste gate actuator and found that the seal had totally blown out and was losing boost constantly. The only time it would pop the over boost code was when I really got on it to pass someone. You might look at your waste gate actuator also.

 

If I catch anybody poking a hole in my tank... I'll poke a hole in them! My mileage dropped off considerably this winter. Between ulsd and winter blend I'm only pulling 17 on the highway at 70mph.

 

Mine doesn't get very good milage at 70mph...60mph or slower gets mine in good shape.