EFI fuel systems normally require two filters: One before the pump (called a "pre-filter") and one after (the "post-filter".) The job of the pre-filter is to remove contaminants that might find their way into the fuel tank before they reach the filter. Modern high-performance EFI fuel pumps have very tight tolerances, particularly on Gerotor pumps which are the most common performance design. A single hard piece of debris can lock the gears on this style of pump and burn out the windings in a matter of seconds. Even if your fuel pump manufacturer provides a warranty, it is an easy matter to inspect the pump, determine the fault was ingestion of debris--and immediately void the warranty.
There are several styles of pre-filter. Besides the inline fuel filters listed on this page, it is also possible to use an in-tank filter if you are running an in-tank fuel pump. These are referred to as "sock filters" and are generally supplied with the fuel pump at the time of purchase. Besides providing adequate filtration to protect the pump, a pre-filter is, to some degree, self washing. As fuel sloshes around in the pump it tends to knock bits of debris loose from the sock filter, keeping it clean.
In addition to a pre-filter, all EFI fuel systems should include a post-filter. Holley offers both 40- and 10-micron post filters. The role of the post-filter is to remove tiny debris that can pass safely through the fuel pump. This small debris will negatively affect the fuel injectors if allowed to continue through the fuel system, plugging the screens and wearing the delicate internal valve components. Each filtration level has its benefits. A 10-Micron filter will obviously provide superior filtration but presents a greater maintenance requirement as it will plug more quickly. The 40-micron filter is a good choice where regular maintenance is not practical or likely.
During the design of a fuel system, it is worth while to consider the installation of one of Holley's new Hydramat fuel reservoir systems. The Hydramat fits inside the fuel cell and provides a 15 micron filtration level. By running a Hydramat in the fuel cell, you eliminate the need for further filtration. The filtration capability of Hydramat is actually a side benefit. It virtually eliminates fuel starvation caused by g-forces and low fuel levels. Though it is not inexpensive, by eliminating the need for two fuel filters and their related fittings, this greatly offsets the cost associated with Hydramat.
