A customer presented a Renault Laguna (diesel) with 180,000 miles on the clock, reporting a combination of problems
– Engine spluttering on ignition
– A misfire at 2,000 revs
– ‘Service’ light showing on dash before service was due
– Smell of burning oil (at end of journey)
All these pointed to low fuel pressure and causes include
– Worn injectors
– Worn high pressure fuel pump
– Faulty pressure regulator valve
– Worn turbo charger
I initially performed an in situ leak back test of the injectors as this was the quickest and easiest way to ascertain if worn injectors were the cause. This test did not reveal any faults so I then carried out a data run to check the various engine management sensor readings, in particular fuel pressure. This involved holding the revs at 1500 rpm, and while doing so the revs increased uncontrollably and emitted a large volume of black and grey exhaust smoke. The engine would not switch off until I put it into gear and let the clutch up in order to stall the vehicle.
This sudden racing of the engine was caused by the failing turbo charger as the wear in the bearing allowed the oil to be sucked into the engine, and consequently the engine was running on its own oil which is why it wouldn’t switch off. Thankfully, the vehicle was off the road at the time.
The poor starting and misfire the customer had noticed was a result of the turbo charger being worn sufficiently to allow a small amount of oil to pour into the intake pipes.
The ‘service’ light appeared because the engine was low on oil as a result of the above, and the smell of burning was caused by the oil leaking out onto the exhaust.
Photo Turbo charger assembly