i just replaced injectors and cross over tubes in my 2004 CR 5.9 Cummins with new ones. I torqued them to specs. i still have a slight puff of black smoke when slight acceleration from of idle. It disappears when put under power, but wether warm or cold still puffs slightly when accelerating from idle. According to my over head display mpg's went from 18-21 before injector replacement to 10-13 mpg after. i am not showing any white smoke, nor is there any miss or shutter in idle. i understand that new injectors have a break in period so my mpg's will get better with operation.

What concerns me is when its at idle I can watch the mpg drop at a constant decreasing rate below 6.0 mpg. Should the mpg not increase while idling and drop when under acceleration?

I have checked my oil. There does not appear to be any significant difference in the level. Could this be a faulty injector, leaking coss over tube, sensor, turbo, or am i just looking for issues that are not there?

 

First thing....DO NOT TRUST THAT "LIE O METER" ON THE OVERHEAD. That useless piece of junk is worthless. You NEED to hand calculate your mileage.

Now, mpg means what? MILES per gallon. If you aren't going anywhere and you let your engine idle until you run out of fuel, how many MILES did you go? Well you went 0. So, no your reading on the lie o meter is going to drop as you sit there and idle and not go anywhere.

 

yeah, my lie-o-meter says I'm getting 20mpg while black coal is rolling out of the tailpipe...

pay no attention to that thing.

 

Thanks guys. I didn't know my "lie o meter" was designed to drop when standing still. I thought before I had changed my injectors my overhead mpg display went up when sitting idling. Maybe I am wrong.
Can anyone tell me where the sensor is located that distributes the mpg read out and how it works Wrapping my views after some thought you are right at a lower speed you are travelling less miles per hour therefore less miles per tank gallon until an average speed is attained, but Why does my litres per 100kms not drop as my mpg when static as well?

Can some pleae explain where the sensor is is located for this lie om meter and how it works

 

its actually all controlled by the ECM. theres no single sensor per say for it...its doing calculations based off vehicle speed, fuel level sender, throttle position, engine rpm, and engine load.

any kind of aftermarket modification to the engine will throw it off.

mine says my average fuel economy is like 18.5-19.5 when in reality its 13-14mpg

 

Oh I got it. Took me a while! So I don't have anything to worry about? All systems normal with the drop in mpg with new injectors? I am told the slight puff of black at acceleration when idling in park is normal This does go away under power!

 

nothing to worry about. and your mpg's should go down while sitting still, because you are burning fuel still, but you aren't moving. if you sat still idling for long enough it might change to gallons per mile! lol

Just hand calculate your mpg and keep track of it that way. (miles traveled since last fillup divided by # of gallons it took to fill it up again.) make sure you top it off every time the same way to do hand calculations. diesel fuel is foamy when you fill up and might be more foamy on some days than others which will cause the fuel nozzle to click off too early. also reset your trip odometer every fillup and that will give you an accurate avg mpg...

example if you went 700miles from last fillup and took on 30 gallons at fillup, you got roughly 23MPG

 

thanks again

 

The black puff from stop to go is normal. It from more fuel being introduced to accelerate and the delay from the turbo to provide more air. Black smoke is ok, white means you have issues.