X15 noise and lack of power on a hard pull.

[marek4792]

It can run that low, the problem is that the liner and block design cannot handle low rpm high torque operation. The ISX and possibly X15 is known to sink liners because the way the piston and rod is moving in the cylinder, it is actually pushing the liner towards the exhaust side where most failures become obvious. Lugging the engine causes most of the liner vibrations making it eventually sink on the exhaust side. Also poor deck height plays a role amplifying the issue as well.

Sounds like your gearing is right for direct drive sucks it's a 10 speed, 13 or 18 would greatly benefit the truck especially if you get it reprogrammed or put a manual in it. Another thing, cummins could give a less of a poop about the initial sales because they make their bank on aftermarket parts! Design it to last long enough for it to fail conveniently outside the warranty period so they can screw you dry on a $25-30k overhaul at 500k miles. My buddy went through this very scenario at 450k miles sunk a liner causing head gasket failure, decided after the overhaul and having to start replacing parts he'd be more financially viable trading it for a brand new one (Cali based) and starting fresh again.