ISM Cummins CM875 Power surge

[Nilao]

Unplug the egr valve and road test, if it still acts up then install a mechanical fuel pressure gauge and make sure the pressure is about 120 psi at 1200 rpm. I would also check for aerated fuel, but you need to install a clear test line between the suction line and pump for that.

You could just put a block plate at the mixer pipe and not allow any egr gas into the intake and see if the surge goes away.

I think the ISM 875 suffers the same flaw the ISX 870 had. The EGR actuator motor is on the hot side and burns out yearly. I'm thinking the valve is stuck open and allowing egr flow when it should not be allowing any. The ecm sees the flow and flags the derate. Just my gut feeling here.