CAT C9 Fuel Injector Intermittent Electrical Connection in Engines Posted May 22, 2017 · Report reply Hi. I thought I replied, but for some reason, the answer did not "take". I believe that Mustang's thinking was that the injection system would be prone to tripping a code on the weakest-performing cylinder if the system pressure was low. They had found pressure regulator problems on other CAT engines, and mine showed some indications (pressure was in the mid-60 psi range, when it should be in the low 70s). The same reasoning applies to the filters.....common problem if you get a load of bad fuel, lowers the system pressure, etc. In retrospect, they were barking up the wrong tree.....all the indications were electrical on cylinder #2. But since they couldn't find an electrical problem, they looked in other areas. The injector harness itself was not that expensive ($121)......it was the labor that ran up the total bill (just shy of $1500).