Discovery TDI smoke and power loss

Keith · 2009-08-17T15:13:59+00:00

I have a 1997 Discovery 300 TDI that I've had from almost new. I'm in London, UK. The Disco is not used a lot these days but is NOT used for short stop/start around town journeys; it's mainly for longer trips. It has only 78K miles on the clock, has been serviced regularly from new and has done about 2000 miles since the last service in April.The other day, the day after a trip to Norfolk from London, I noticed some black smoke when pressing the throttle fairly hard at slow speed. Power also seemed a little down when accelerating at higher speed. The smoke seemed to get more frequent as the day went on but otherwise the car seemed OK.Next day I set off back to London, about 130 miles away. I kept the revs low at 2200-2500, and speed lowish at 40-50 mph in 4th. Everything seemed OK at first but after maybe 30 miles power was seriously reduced and there was black smoke when only slight extra throttle was applied. After a while I had to increase the revs to 3000 plus and drop down to 3rd or 2nd when going up even a slight hill. If I dropped the revs the engine laboured.This went on for maybe another 40 miles with speed between 25 and 45 mph. If I gave the engine any extra throttle I got black smoke. Performance seemed to get better when I got to continuous dual carriageway and did not heve to keep slowing for roundabouts and junctions and I was able to use 4th gear at 2800-3000 rpm. By the time I hit the M11 motorway I was up to 60 mph and down the M11 I could even use 5th and go over 75 mph. After I left the M11 the car seemed more normal but still seemed down on power with a little black smoke when the throttle was pressed hard. I got the few miles home from the motorway without difficulty.Before I take the Disco in to my local independent LandRover garage has anyone any ideas what might be the cause of this?