TLC Keeps Bimmer Diesels on Top

October 23, 2015 | By | Reply More

Since they were introduced in 1983, BMW diesels have shown themselves to be very durable and dependable. That is, if they receive proper maintenance. No? Then you’ll need to do some diagnosis before you fix anything.

Tens of thousands of loyal, enthusiastic BMW diesel owners and drivers enjoy tens of thousands of miles of spirited, trouble-free economical driving year after year. Now and again, however, driving is not so trouble-free and problems intrude on the pleasures of driving a BMW.  Here are a few issues – some major, some not — that bear reporting, basically falling into three broad areas:

  • loss of power
  • fuel delivery
  • engine damage

Turbochargers are a probable cause of power loss

Diminished power is perhaps the most common diesel ailment, and – almost   universally — falls on turbocharger-related issues. BMW diesels rely on turbochargers to give them the punch needed for superior performance, but can fail to operate normally causing significant power drop, or fail and require significant repair.  Things that can have a dramatic effect on a turbo’s life include:

  • Loose or split vacuum hose
  • Insufficient or incorrect oil
  • Ignoring normal service intervals
  • Clogged crankcase breather
  • Oil feed line blockage

If turbo failure is suspected, but no definitive symptoms are apparent, a quick check of vacuum pipe connections and the condition of the vacuum reservoir is in order — the problem could be simply a disconnected or cracked vacuum hose. If these are okay, a diagnostic scan can show DTCs (Diagnostic Trouble Codes) specific to turbo operation. Some diesel turbo-related codes, symptoms, and causes include:

  • 3F01 Boost Pressure sensor inactive. There is one pressure sensor located above the turbo and another one under the inlet manifold that control the EGR valve. Removal and cleaning of this valve may clear it, but replacement may be required.
  • 4521 Boost pressure control pressure may be too high.
  • 4530 Boost pressure control pressure may be too low. This can indicate clogged variable vanes in the turbo, and it may be necessary to check vane operation manually.
  • Turbo Whistle.  Wear and tear over thousands of miles of spirited driving may cause some turbos to whistle more than others, but if the whistle is more of a scream that sounds like a police siren and the engine has no power over 1,000-2,000 rpm, check the play on the turbo’s shaft ASAP.

Remove the air pipe to the turbo’s inlet after the engine is cool and grip the turbo’s shaft between thumb and forefinger to check side to side (radial play) and end to end  ‘float’ (axial play) on the bearings. Axial float should be 0.025mm to 0.1mm which can hardly be felt, while radial float is normally 0.3mm to 0.6mm, felt as a definite rocking. A dial gauge is required to accurately measure float, but if either axial or radial float feels excessive the unit may need immediate attention.

Unusually high oil consumption with blue exhaust smoke can indicate worn turbo seals, and in very rare instances the engine can begin


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Category: Engine Mechanical, the bimmer pub

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