This weeks diagnostic dilemma :- This case study actually goes back eight months but i am only posting it now as we have been waiting for a new inlet manifold for all this time .
Originally we were asked to take a look at this vehicle as the customer had an ongoing misfire which a Ford dealer couldn’t get to the route cause of. The vehicle had an array of new parts fitted including new plugs and coil packs but still presented with the same faults . The ecu had recorded misfires on number eight cylinder and random misfires all related to the n\s bank of cylinders . We started by trying to replicate the customers described fault and testing on the rolling road we were able under the correct conditions to produce the misfire and a flashing engine management light and the same faults were recorded. The conditions were quite specific , the engine need to be hot and covered 5-10 miles then after a short burst of acceleration and cruising on a light throttle it would misfire.
We started with testing the ignition system on an ossciioscope this was perfect so we moved onto the injection system , removing all eight injectors we tested these in house in our Asnu testing bench again these tested perfectly. At this stage we re-evaluated the issue with regards to any common components that only related to the one bank where the misfires occurred. The only other components we hadn’t evaluated where the inlet manifold flaps . We were able to carry out a live test operating the vacuum controlled solenoids and watch the control arms move they appeared to operate normally but we couldn’t actually see the flaps move being enclosed inside the plastic manifold . We came up with a solution to be able to see the flaps move whilst actuating the solenoids , this could only be carried out with the engine not running because we needed to see the flaps we had to remove the injector rail and injectors and use a endoscope to see back up to the flaps . The solenoids can be switched via a diagnostic tool but as the engine is not running we had to generate a vacuum supply to both actuators so they could move. This is where we found the issue even though both actuator arms were moving the n\s swirl flaps didn’t move this was disrupting air flow under certain conditions and causing the misfire .
With the manifold removed it was very clear that the diagnoses was correct and a new complete manifold resolved this issue pity it took eight months to arrive .
