Internal Diesel Injector Deposits (IDIDs) have been known for some time. With the latest powertrains becoming ever more sophisticated and reliant on efficient fuel delivery, the necessity for a continued focus on limiting their formation remains. Initial studies probed both carbonaceous based/ashless polymeric and sodium salt based IDIDs. The reported occurrence of the latter variety of IDID has declined in recent years as a result of the removal of certain additives from the diesel distribution system. Conversely, ashless polymeric based deposits remain problematic and a regular occurrence in the field.The body of work presented in this contribution is an extension to that reported in SAE paper 2014-01-1401 which showed how a particular Fuel Borne Catalyst (FBC) additive has the ability to significantly reduce the formation of ashless polymeric deposits formed from the reaction of Poly-isobutylene Succinic Imides (PIBSI) with fatty acid and the ability for the same additive to also be neutral towards the formation of sodium salt based deposits.There has been significant debate regarding the composition of such deposits, particularly for the ashless polymeric type. For this reason, here detailed is a full chemical analysis of the deposit formed in the ashless polymeric deposit programme conducted. The protocol developed can be easily run and provides a clear view of the composition of this type of deposit. The techniques used - Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (SEM/ EDX), X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToFSIMS) amongst others - permitted the identification of the deposit chemistry present on the injector surface. The results were further confirmed comparing injectors which were shown to seize with contaminated diesel and others that remained free as a result of using the FBC additive.