I've never had the opportunity to ride or run one of the EMD Tier-IV units, but I do have a story that seems relevant to this conversation.
CN had been testing a pair of EMD demonstrators (EMDX 1605 and 1606) through 2017. They got good reviews from crews but the test period abruptly ended after both units (on different trains) failed out on the road in a -40 Saskatchewan winter's night. Less than a week later CN placed an order with GE for 200 new units, this order was later increased to 260.
A short time later our head ESO (Engine Service Officer, that's Canadianese for Road Foreman) went for a ride on my train, and we took the opportunity to quiz him about the new locomotive purchases. He said that the EMD Tier-IV units used too much fuel and replacement parts were more expensive than GE stuff, and the enroute failures were just the icing on CN's decision to continue buying GEs.
I should note that early production ET44ACs and everything built at the Fort Worth plant during its first year or two seemed to have A LOT of problems, far more than just the higher fuel consumption of EGR engines. The computers would crash all the time, air lines and wires would break off, and plenty of little stuff like light switches would snap if you so much as brushed it. Just poor build quality all around.
But I have to admit our GEVO fleet seems to have been pretty reliable over the last couple years, either they or our mechanical department must have done a pretty good job at tracking down and fixing the problems.
