98 12v qc 4x4. I am getting 13 mpg. Thats with #2 and 4 oz per 10 gal of power service and marvel mystery oil. It from what I remember from driving other ctds growing up you could pretty much drop the clutch in second. I have to give it throttle to keep from dying. i changed the fuel filter and cleaned the pre-filter/screen. If there something i am missing? i thought this truck would get better mileage than that and the 24v had a lot more power it seems.

 

is it blowing white smoke? Is it making boost, try checking the intercooler boots

 

no smoke that I have ever seen. I think it is making boost because when you get it higher up in the rpm range it seems to want to wake up. I know I need to get gauges, but I can't decide which ones I want.

 

My 97 12 valve had the same problem, mainly attributed to ULSD, I think. I took it to ProMotors in Goshen, In and Byron installed a stage 1 fuel plate. This truck pulls like a locomotive now, and is unstoppable. My mileage also went from 6.5 to 8.6 towing, and from 11.3 to 16.6 when not towing. This might be something to consider. Also consider an HHO generator. I have bought one, but do not have it installed yet. Am having it installed 4/17/08, and will know more after that. Will keep you posted on mpg improvements, if any. I also plan to change my gearing from 4:10 to 3:55, hoping this will help my mileage also.

 

i would recomend checking air or exhaust extriction first. next thought would be with a stock truck, have the timing checked for slippage

 

The stock intake has a new filter and the exhaust is a straight-pipe.

 

You can't make power without boost. You need to measure the boost vs rpm vs load to see if you have boost at the right time. Get a boost gauge. Your high fuel consumption might be a result of low efficiency from lack of boost. Boost should come on strong about 1500 RPM. Adjust your idle to 850 for more idle torque.

 

changed the fuel filter today. It looked fine this time. Last time it was black. I did notice that there is a hiss after sutdown for 10-15 seconds. Is this normal?