The innovation of the computer-generated fault diagnosis has led us to lose sight of the basic operating principles of the diesel engine. Unfortunately, the fault codes don't always pinpoint the problem but rather bring up an array of codes that could be either this or that. Being told: "we have tried this and it has not helped" or the best one, "sorry there are no fault codes so we can't find anything", is extremely frustrating and can be costly. Main Dealers, specialists and garages equipped with expensive and sophisticated diagnostic equipment still seem to struggle.

We have put together this guide to assist you with faults regarding diesel fuel injectors and pumps, DPF diesel particulate filter cleaning and other faults relating to diesel vehicles.

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We can generally understand what is wrong with a diesel engine by the colour of smoke emitted from the exhaust. There are three basic colours - black, white and blue.

Black Smoke

This is due to an air to fuel ratio imbalance, either the fuel system is delivering too much fuel into the engine or there is not enough clean air (oxygen ) a few things to look for:

  • Faulty injectors (injectors need attention at about 100.000 to 120 000 miles) check for injector blow-by.

  • Faulty injector pump, this is more relevant to pre common rail systems.

  • A dirty air cleaner or restricted air inlet, check swirl flaps if applicable.

  • Turbocharger or intercooler faulty

  • Problems within the cylinder head, valves clogged up due to faulty EGR (exhaust gas recycling unit)

  • Engine timing problems, check cam to crank timing.

White Smoke

Normally means that the fuel injected into the cylinder is not burning correctly. The smoke will burn your eyes.

  • Engine/pump timing out

  • Fuel starvation to the pump causing the timing of the pump not to operate correctly

  • Low engine compression

  • Water/petrol in the fuel

  • Injectors dribbling.

Blue Smoke

The engine is burning engine oil

  • Worn cylinders or piston rings

  • Faulty valves or valve stem seals

  • Engine over full with engine oil

  • Faulty injector pump/lift pump allowing engine oil to be mixed with the diesel

Should you have an enquiry or wish to place an order with us please email us your enquiry, phone us or complete and submit the enquiry form.


Should you wish to send units in for testing or repair, please box them up well and either send them in or contact us and we will arrange collection. Don't forget to place a note in the package with your contact details.

Telephone: +44 (0)1939 291155


Email: info@uniteddiesel.co.uk



Unit 35, Atcham Business Park



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