Fuel Leak Back Test - Monday 10th November 2014

Leak Back Test Kit

Today was a resumption of the practice Fuel Pressure Task from last Tuesday, on the Citroen C4 1.6 HDi (CI) engine.  We commenced by re-hooking up both the Carman Diagnostics scanner and the Picoscope to double check our results from the previous session.  The issue with the vehicle is one of a slightly "uneven idle".  Using the Carman Diagnostics scanner we re-ran a search for codes which turned up an open circuit fault on Injector Cylinder 1 (which according to Autodata is the cylinder on the right hand side of the block).  This was disproved by subsequently testing each injector for continuity using a multimeter set to Ohms.  All Injectors provided a reading of 0.7 Ohms respectively (Autodata says expect 0.3 Ohms).  With the engine running we then disconnected and reconnected each injector's electrical connector in turn, and noticed that there was a noticeable "indifference" (at idle) to the disconnection of Injector No1.  We then re-ran the engine and re-tested the Amperage consumption of each injector using a Picoscope, but in each case the test returned similar performance patterns to one another, both over time and frequency.

Picoscope Pattern of Injectors

Leak Back Kit Connected

By this stage we were scratching our heads and decided to call Carl Black in to present our findings thus far.  With all our data and results proven, he suggested conducting a Leak Back Test using the equipment pictured top left.  I have never seen this test conducted before so the experience of it's guided demonstration was most beneficial. The equipment is fitted to the fuel return side of the injectors, which is not under the same extreme pressure as the delivery side, and basically collects the excess fuel delivered to each injector (which would otherwise return to the fuel tank), through tubes into small indexed pots.  Once the equipment is fitted the engine is started and the pots then collect the fuel.  If all injectors are performing equally then each pot should collect an equal amount of fuel.  This test proved that there was definitely an issue with the injector on Cylinder No1 and in fact, an uneven delivery over a couple of injectors.

Collection Pots after Test
(Cylinder 1 RHS)

With our findings duly recorded it was time to start clearing away for the end of session.  Unfortunately, after the injector's fuel return re-connection, there was a slight fuel return leakage issue on one of the injectors, which will be rectified first thing tomorrow morning.  A very interesting and enjoyable task indeed.  Thank you muchly!