CM871 fuel mileage

[superbudy208]

WOW thank you for all the INFO RAWZE this is why I'm here!

When I slow down to 63ish the mpg's get worse, so that's why we try to run 68 to 70 is not to lug the engine end the mileage is not that much worse usually around 4.8 to 5 mpg's , the last tank at 63 was 4.44 mpg's, and 95% of the time the truck is loaded with the most deadhead being around 100 mile if that so far.

When were running the hills it does a lot better at the 1500 rpm range and try to keep it up there in the 1500 rpm range, and yes the balancer was the first thing I replaced and performed a overhead before I ever hit the road

I will get the boost gauge in this week and may have to run the hills in 9th gears about 60 to get the rpms up around the 15 to 1600 rpms range, it will run the hills well at 75 mph in the 15 rpm range, it will shift on hard hills around 1650 rpms but it don't seems very happy about in then jumps the rpms down to the 1300 or so range. and yes the mileage going down with the speed was a shocker we've been trying different speeds an watch the mileage

I will start looking for a better set of rear gears what gears would you recommend??
i do understand the auto use's more fuel, but once your on the highway it stay's in 10th or 9th if we hit a hill and loose speed and the door does stay shut unless its for fuel about every 900 miles or so depending on the price along the route's.

the EGR valve and cooler were replace not long before I got the truck the IMAP was plugged up so replaced that also found the BARO sensor was plugged and the first full tank after replacing the BARO was the best at 5.6 but has gradually got worse each tank, and I made sure all the ports on the exhaust differential pressure were clean and clear, but I have not checked the exhaust back pressure sensor yet. I do have a nexiq code reader and did notice when I pull the data there are some important things missing like intake air temp and intake manifold pressure say not available so I'm kinda leaning towards some tuning issues also on top of some other isssues.

No the truck is not de-mandated but the ECM and the fuel control module has been replaced when the engine got an in-frame 285k ago, and yes this is my first truck and yes its just beginning, and yes after every run I try something new and spend my off time working on it and that is an issue I enjoy it but coming to a loss on the fuel mileage at the moment, i never really thought about the spec's of the truck when I bought it! (stupid me) but I did not know I've been working on the on and off for the 5 years or so mostly service work, never any issues like this, so its been interesting to say the least.

Where are you located i would love to bring my truck to you and go over it! this fuel mileage is making this tough!