Hopefully they can isolate the cause. Engine problems at throttle back can point to super-absorbent polymer (SAP) contamination. The reduced fuel flow causes the fuel temperature in the HMU to increase, dessicating the globules of SAP creating small spheres in the 10-15 micron range that can jam the main metering valves. That was what happened with CX780. Most fuel hydrant trucks have SAP laden filter monitor elements, so the lesson with CX780 will be repeated until the industry learns.