using graduated vials (or syringes) is the standard diagnostic to identify a failing injector. Internal Pump Failure
If you own a Renault Clio equipped with the famously efficient (yet notoriously finicky) 1.5 dCi engine (K9K), you have likely encountered a moment of dread: the illumination of the service light, a drop in performance, and a cryptic code staring back at you from an OBD2 scanner—. df137 renault clio 15 dci link
Late DF137s (2009–2012) with a DPF suffer from clogging if used only for short urban trips. The required regeneration cycle (post-injection of fuel) never completes, leading to oil dilution and eventual turbo failure. using graduated vials (or syringes) is the standard