HORRIBLE fuel mileage

[Redland1]

My mpg is down to 4mpg and the last fill up was 4.33mpg.Engine is an 04’ ISX 15 535 hp in an 03’ international 9900i.
3.90 gear ratio and 13 speed.Driving habits have not changed and I’m still hauling the same commodities with the same trailer only difference is that I’m loading 6k lighter bringing my gross to 96k.The only thing that has changed or been done to the truck is a demandate,EGR block plate,and the plate that goes where the EGR entered the intake.I did have an exhaust leak that I could feel around the EGR block off plate when I first installed it and I tightened it down even further and I can no longer feel it at idle but don’t know what it’s doing going down the road.What do I need to check so that I can get my fuel mileage back in check.Prior to the demandate I was getting 5.5-6mpg at 102,000lbs gross.Demandate was done with stock 535/1850 torque..

[Redland1]

Want to mention that the turbo goes up to 40psi now and saw it go a hair over that yesterday.

[Mr Hagg]

Check your exhaust back pressure sensor reading.

[marek4792]

Check the silcone hose on the back side of the egr cooler it's a PITA to get to, but could be causing issues too.

[Redland1]

(01-26-2023 )marek4792 Wrote:  Check the silcone hose on the back side of the egr cooler it's a PITA to get to, but could be causing issues too.

With it demandated what will I be checking for in the hose?

[Redland1]

(01-26-2023 )marek4792 Wrote:  Check the silcone hose on the back side of the egr cooler it's a PITA to get to, but could be causing issues too.

I removed the pipe that went from the EGR to the intake manifold and put a blocker plate at the manifold.

[tree98]

Boost leaks, leaking fuel somewhere, bad injectors are a few that come to mind. Is it smoking more than usual?

[Rawze]

(01-26-2023 )Redland1 Wrote:  Want to mention that the turbo goes up to 40psi now and saw it go a hair over that yesterday.

40 psi will eventually kill than engine. Your turbo is choking the engine at that boost level. CM870 ISX cannot take that boost level.. in fact.. NO ISX can take boost that high. It should not be more than about 37~ish max psi on it in a hard pull.

just for reference.. With no egr ... it only takes about 38~ish psi to make 900+ Horsepower with an 870 or 871. ref: http://rawze.com/forums/showthread.php?t...03#pid6803

I have seen people blow holes thru pistons at 41+ psi on the isx, so a person is dancing with razor-blades of they are letting their engine get to 40+.

If that turbo was set too aggressive then it will kill the fuel mileage across the board + eventually harm the engine.

If it was someone who made the program recommended by the forum here, then you should get with them to have that boost lowered back to normal levels, and to remove any aggressive numbers in the lower fueling ranges. -= It is not "snappy" that you want from a CM870 and its turbo settings, the air operated turbo is just too clunky for that. It needs to be a bit "lazy" .. and this will make the fuel mileage better.

Also... if it was not by someone recommended from here.. the you should know that bad delete programming is a plague.. so depending on who did it.. that might be a big part of the problem. Am curious who did the programming (pm me if you don't want to state it publicly) and/or send me a copy of the program for review.

[RollinCoal]

Ole 870's are a bit lazy but very reliable (if the tune is right)