We have seen some claims by one or two forum experts, one even suggesting the high pressure Common Rail Pump could run dry. This is complete nonsense. In some instances I agree that an inadequate supply causes problems, e.g. some rotary fuel pumps are very sensitive to restriction (Bosch VP44, Denso ECD-3 & ECD-V4). But in most systems around today, including Common Rail, secondary (final filtration at 2 to 5 micron) is the best thing you could do to increase the life of your fuel system & safeguard against expensive repairs due to fuel contamination.
Some modern vehicles e.g. Toyota, have a restriction indicator to alert the driver if there is a restriction by illuminating a warning light on the dash. A restriction sensor mounted on the factory filter senses any restriction upstream from that point back to the tank, but not a restriction downstream of the sensor, i.e. between the factory filter & the high pressure pump. In the extremely unlikely case of a secondary filter becoming blocked, the restriction sensor would not detect this, however, the worst thing that could happen by having a reduced fuel flow or restricted supply to the high pressure pump is a loss of engine power, or perhaps a surge. These two symptoms are common when a filter becomes blocked, or possibly if a tank puck-up or tank vent is clogged.
We have never seen a fuel restriction lead to the failure of a Common Rail pump. The evidence that a Secondary Filter will not “create more problems than they fix” is with the tens of thousands of Secondary filters currently fitted to vehicles all over Australia. There have been no pump failures, system damage, or any symptoms whatsoever. We have saved hundreds from damage & failure from contamination. We have, however, seen hundreds of Common Rail pumps fail due to fuel contamination where no additional fuel filter has been fitted. Enough said.