Are you reinstalling your FF640 injectors after having them installed for 6 months or more? We recommend a reinstall kit. The older or more unknown the provenance, the higher kit type we recommend. We only recommend the Lite kit if you are reinstalling your own injectors, rather than injectors you bought used. Also, these products are reserved for those with Flow Force branded injectors, either purchased new or used.
Lite: Bottom cushions, fuel rail adapter o-rings, and dielectric grease
Standard: All lite components, plus injector top o-rings, new connectors, and filters
V3 Upgrade: All standard components plus the new-style fuel rail adapter with filters
V2+3 Upgrade: V3 upgrade plus fuel rail spacers