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Chris Davies

Black smoke under load

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Hi, my 200tdi 90 has recently started to give out black smoke, not loads but can see it through the mirror. Usually notice it going up hills when I open up the throttle. Particularly noticable when towing (guess I'm opening the throttle even more when towing).

What might be causing this, what can I check, adjust etc

Cheers

Chris

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had a similar problem on the missus 300tdi disco, then the head gasket went, hope you dont have that problem

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Black smoke is due to incomplete combustion. Often because the engine is not provided with enough air to burn the amount of fuel injected. But it could also be due to poor atomisation of fuel by faulty injectors, or low compression (not enough heat for combustion to start at the correct time.

Insufficient air could be due to:

  • Restrictions in the inlet before the turbo compressor - e.g. air filter, etc.
  • Restrictions after the turbo compressor - de-lamination inside hoses, etc.
  • Air leaks after the turbo compressor - gaskets, hose connections, etc.
  • Faulty turbo (or waste gate) not producing enough boost/air flow - worn bearings, damaged impellers, stuck waste gate, etc.
  • Blocked intercooler

Measuring boost pressure is a good start to finding your fault.

Do you have any other symptoms, such as harder to start (another indicator of low compression), using water, etc. ?

The governor on the fuel injection pump controls the amount of fuel injected. As you put your foot down to accelerate or on hills or towing, the governor increases the fuel rate for the load increase. The governor was initially calibrated for a correctly operating turbo and induction system and has no way of knowing that there is a problem with air mass flow.

Black smoke is often associated with high exhaust gas temperature, which can cause engine and turbo damage.

If it is due to faulty injectors, it often leads to scored cylinder bores and damaged pistons.

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Thanks for the comprehensive reply Bush65, plenty to check there.

A turbo boost guage is something I have been meaning to get for a while now. Anyone got any recommendations, where to buy or indeed any to avoid.

Cheers

Chris

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Hi when i got my 300 tdi it had the same symptoms I said to myself 'it must be the injectors will change them' My priority at the time was the cambelt since i didn't know when it had last been changed. Anyway when i did get around to the cambelt i discovered the IP was a bit 'out' i reset everything and changed the belt-now it's nowhere near as black smokey as before.It only blows a bit black when i'm a bit heavy footed in fourth or fifth.

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