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volkswagen golf estate: what would cause a black sooty discharge

 
350matt's Avatar
  • Answered by:350matt
  • Engineer - BEng Hons
  • Positive Feedback: 94.0 %
  • Accepted Answers: 469
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Customer Question

what would cause a black sooty discharge from the exhaust and an acrid smell. The car is otherwise driving well and is not showing any problems on the dashboard display. The car is a golf estate.

 

Country: United Kingdom
Make: volkswagen
Model: golf estate

Already Tried:
an annual service with my local garage which found the emissions were higher than they should be

Submitted: 264 days and 19 hours ago.
Category: VW
Value: £21
Status: CLOSED
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Expert:  Cardoctor74 replied 264 days and 19 hours ago.

Is the engine light on?

Customer replied 264 days and 19 hours ago.

no no warning lights on dashboard

Customer replied 264 days and 19 hours ago.

Relist: Other.
i have not received any help at all yet. i have paid 20 pounds for nothing so far

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Expert:  Cardoctor74 replied 264 days and 16 hours ago.

I'm am so sorry for the delays there were site issues and internet issues . The most common issues are dirty fuel injectors or a faulty mass air flow sensor were these checked ?

Customer replied 263 days and 4 hours ago.

Relist: Other
We still need help and are being asked for extra info please be very precise as to what info is needed - there really is nothing showing. Engine runs smoothly, however there is an acrid smell when car has been driven which increases in intensity if fans are used in car (obvious I suspect) gas emmissions were high at MOT but were reduced by garage to pass MOT. Smell has returned suggesting emmissions higher again and sooty deposits are left on drive after car is used. No engine management lights showing and we are now using the cleanest unleaded fuel. If you need anymore info please detail.

Accepted Answer

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Expert:  350matt replied 263 days ago.

Hello

Ok if the engine is running rich to extent of leaving soot marks on the drive then I'd 1st suggest getting the fuel pressure checked as if this is high due to a faulty regulator this can result in over fuelling

I'd also check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

Also replace the spark plugs if any of them fail this checklist:

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Expert TypeEngineer - BEng Hons
Category: VW
Pos. Feedback: 94.0 %
Accepts: 469
Answered: 7/21/2012

Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing

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Customer replied 263 days ago.

thank you for getting back to me. when the car was serviced they found a small crack in the exhaust pipe which they fixed so will check the fuel pressure and the spark plugs and go from there.

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Expert:  350matt replied 263 days ago.

Hello

if the crack in the exhaust was before the oxygen / lambda sensor then its quite possible that this was the issue

let me know if I can help further

 
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