I'm by no means a Cummins expert but on my Duramax I was getting terrible mileage and it was smoking a lot. The problem ended up being a stuck open EGR valve, an idea worth investigating at least. Even with the issues you have had with the truck I think you will like it in the end.
JB
JB, thanks for the feedback. Fortunately I have no ERG valve because it’s the 5.9L before Chrysler and Cummins made the 6.7L with emissions ERG valves and DEF.
But I learned a few things tonight while talking with the guy who wrote the tune. And I’m not getting as bad of fuel economy as I had figured. Don’t get me wrong, I’m still leaking fuel but here is how he broke it down...
The estimated 25 mpg was at 55mph with a manual and stock truck with highway tires. I have 33” BFG KO2 ATs which will have a negative effect on my mpg by about 12-15%. I’m running a 48RE automatic trans. Also, I’m running King Ranch front bumper which will have a negative airflow dynamic and I was driving 75 mph. All things considered, I should be getting about 17-20 mpg based on these items (15-17 if going 70-ish and closer to 20 if going 55). Add in a small leak and I’m down to 12-ish.
He was telling me the devil is in the details. These were items we didn’t discuss before I installed the fuel economy tune. So he’s going to look at the data logs and see if he can figure out the gap. And I think I still have a high pressure leak only under fuel rail psi over 6000. Why that number, cause at idle less than 6000psi I can’t find a leak but if I drive it and then park over dry pavement like I did today, I drip drip drip fuel.
So I’m chasing that still but at least it isn’t as bad as I originally thought. The delta is between 12 and 15 mpg based on what and how I was driving Monday. That’s 3 miles per gallon difference or 1/4 of the amount I thought I was leaking. I thought I was leaking 5oz per mile but its probably more like 1oz or less per mile. That means over 132 miles I’d lost a gallon to dripping fuel. Much more manageable but still needs to be solved.
On a separate note, my radio broke and the aftermarket head unit I installed didn’t work... there is something wrong with it. Sheesh!
Sent from my iPhone using a facsimile machine.
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