I have a E39 525 TDS and its not starting up normally. I can get it to start up after about 90 seconds of cranking the engine. In the mean time it is blowing out grey smoke whilst attempting to start-up. This is probably unburn or partially burnt fuel.
Once the engine is hot, restarting it is no problem. This indicates that the failure is primarily in heating the cylinders to get the engine going.
I tried to diagnose the problem, it appears that there is no current/voltage to the glow plugs. Looking at various web sites, it would appear that the problem may be with the glow plug relay.
Can anyone advise where I may locate this relay on an E39 1998? Pictures would be most helpful. It is most probably in the sealed compartment under the passenger pollen filter (I am in the Uk so thats the left hand side of the car from the drivers view point).
I look forward to hearing from anyone who has experience or knowledge of this type of problem.