Hi Glen,

I will try to help if I can. We first need some live data to go on, the fault code needs pining down to which way the fuel pressure is deviating. Then we can look at what could cause the deviation.

Can you run the vehicle and look at live data for nominal or desired rail pressure along with actual rail pressure.
Graph the results.
Run the vehicle over the full speed and load range, this should tell us which way the fueling is going.

Next record the IMV duty cycle at the high pressure pump at the same time as the other two and we can look at the relationship of the data.

Regards Mark