February 2020

FEBRUARY 2020 AFTERMARKET 31 EYEBROW www.aftermarketonline.net good so the engine should start but why wouldn’t it? This is where it pays to step back for a moment and evaluate what you know already and what you should do next. Smoke/air pressure An engine in its simplest form is an air pump. We know it needs compression, fuel and air to run. With what seemed to be good compression, and from what I had heard, also good data from the scan tool, with limited resources, I decided the next test would be to see if any smoke was being emitted from the tail pipes. This would show if there was any sign of fuel delivery to the engine. With good RPM and fuel pressure, if the ECU is happy, it should be firing the injectors. There was no smoke, however when I felt the tail pipes there was no air pressure whatsoever from either tail pipe. Was this a clue to where the issue may lie? My first thought was we have a restriction and the engine cannot breathe, so we are missing the air section of the triangle for the engine to run. I then had a good visual inspection of the engine. Knowing the design well, I decided to open the inlet up to atmosphere by removing the map sensor to see if there was any change. If there was a blockage, this test would prove it and allow the engine to run. In this vehicle, the engine is a V6, so it uses a conventional V configuration. To allow air to flow into both intakes of each bank there is what Land Rover call an intake throttle manifold which also houses the MAP sensor, the EGR inlet pipework and a throttle butterfly flap with a rubber hose to direct air from the intercooler into the manifold (fig1). Removing the MAP sensor would allow air to be released if there was an issue from either EGR valve or upstream from the intake i.e. throttle butterfly, failed turbo just to name a few. On removing the sensor and cranking the engine it now fired into life and idled fairly well, this confirmed we had a blockage somewhere manifold side starving the engine of air. Throttle butterfly flap Checking the clock, we still had some time left allotted for the call out. I decided as it was easy to remove the intake hose to the intake throttle manifold just to see as a quick test if the issue was before or after. Upon removing the pipework and refitting the map, the engine no would not start, again proving the issue was on the engine side of the pipework. Removing the air intake plenum to the throttle manifold then revealed the issue. The throttle butterfly flap used to strangle the engine of air on shutdown had jammed shut and never reopened as the housing was heavily covered in carbon. This butterfly, when working correctly, should spring back open ready for the next engine start. Questioning the customer and his driving style revealed he mostly done slow speed and town driving and used supermarket fuel, all of which were a contributing factor to the issue as the valve sits closely to the flow of EGR gas from both valves. Forcing the valve open and refitting the components allowed the vehicle to be driven back to the workshop for a repair to be carried out. Upon the removal of the entire assembly (fig2), it was found the unit would be better to be replaced as cleaning would not remove all of the carbon deposits and could cause the issue to re-occur. The EGR pipework was also removed and cleaned as a preventive measure along with an oil and filter change and the vehicle was returned to the customer. Further learning Why were there no fault codes stored you ask? Well on this engine the position off the butterfly flap is monitored and it should have stored a stuck closed fault but this may not be part of the software’s strategy so I am unable to answer why. However, this article shows that if you have an issue and no faults are stored, there are tests you can do to find the issue. So next time you have a scan tool connected, grab for example 10 good live data PIDs and store them then learn them off by heart. Once you have mastered that section move onto some more and soon you will build up a good mental library of what good data should be, which helps massively to fix cars! Below: Fig 2