Thread: Strange humming noise off idle

This is a long shot but perhaps someone else has had this problem.

My Disco (1999 TD5, 240K) has just had the head off and serviced (new gaskets, steel dowels, head bolts etc all genuine, skim), had the fuel pressure regulator replaced while it was off (old one just starting to leak - I've kept so I can rebuild as a spare) and a new thermostat. I had it done at a local garage. Car is all back togther - motors runs better than ever, and it runs much cooler - so the problems I was having - overpressurising and losing coolant were probably the start of more serious issues. Plastic dowells were quite sheered.

But......there is a very strange noise that often occurs - a sort of humming sound - just off idle - at about 700-900 RPM. Can best hear it from the drivers seat as it is hard to hear over the rest of the diesel clatter if you have your head under the bonnet.

Doesn't always do it but if i am patient enough I can gently press the accelerateor and, every 2 or 3 goes, trigger the noise - and keep it going for a while - it eventually sort of cycles a bit like a pump coming under and out of load. Gradually the motor will start to run roughly like it is missing on a cylinder. If you just push and release the accelerator quickly it doesn't do it except occasionally as the revs drop through that rev range. Doesn't seem to affect the cars drivability - it's going fantastically - i would just like to make sure it's not something that will cause a problem down the track.

My mechanic has checked for fault codes - none triggered and also monitored the live info while the car is making the noise and none of the readings are out of the ordinary.

Any suggestions? Could it be an injector needs resetting on one cylinder? OR a blockage in the pressure regulator? What ever it is causes a low humming, is intermittent, only happens at low RPM and eventually the car runs roughly.

Suggestions gratefully accepted

Willis

Fluids, Strangy or Randlover or anyone else that knows (!) - I've ordered an EGR bypass kit. In the meantime if I unplug the EGR valve modulator will that trigger a fault?

Willis