QuestionQUESTION: Hi Rob
I have a 2000 Golf 4 2.0 with a persistent overfueling problem. I have had the car on diagnostics and there are no fault codes coming up. When I drive in heavy traffic for longer than 20-30 minutes the car begins to smoke and smell of unburnt fuel. The onboard guage also indicates high consumption. Once on the open road the car seems to "sort" itself out and after about 30kms the fuel consumption normalises. I have had the vehicle at the agents and elsewhere however no-one seems to be able to pinpoint the problem. They initially suspected a dry joint or a circuit related problem and I was also rushed for a new throttle body, an air-mass meter and temperature sender unit with no results. It seems to me logical that this points to a temperature related problem. Does it warrant replacing the oxygen sensors on the exhaust? As you can understand I don't want to go through a costly exersise with no positive results.
I hope you can advise.
Regards,
Mark Burton
ANSWER: Are you sure it is fuel you smell and not oil? Oil is vaporized in the crankcase and the fumes are supposed to vent into the intake but don't always do. The smell is very similar to fuel but different. You'll also get a similar smell if oil is dripping on the exhaust. At the end of a moderate drive, open the oil fill cap and give it a whiff. Is the smell in the cabin like that or like the smell when you are at the fuel pump? When you say you are getting poor mileage in heavy traffic, how bad is it (traffic and mileage)? Is it distinctly different than what you've seen in the past?
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QUESTION: Hi Rob,
No it is definitely fuel and not blow-by. The overall consumption is noticeably higher and the range per tank is less. I should have mentioned that the idling becomes a bit rough to a point where it almost wants to cut out whilst the vehicle smokes and the onboard indicator shows a considerable jump in consumption (40-50lt/100km). This is in bumper-to-bumper traffic for 30-45 mins over 15-20kms. The vehicle doesn't use excessive oil.
ANSWER: I'm not familiar with UK emissions, but if it's based on a similar engine control unit, an ultra rich condition should have triggered the ECU to store diagnostic trouble codes. Is your check engine light on? The mixture control is based on lots of inputs, so to pin it down exactly will most likely need real time diagnostics. I could give a list of likely suspects, but randomly changing expensive parts is not a good way to fix this. Do you have a trustworthy independant mechanic who is familiar with VWs?
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QUESTION: When the vehicle initially had the problem I had the car on the diagnostics and a whole list of fault codes came up. The mechanic then suggested that the likelihood of all of these components being faulty was unlikely and that most of the sensors are reflective of the problem and are not able to work within the fueling parameters and thus the ECU is registering an error. He then suggested that we reset all the errors and see which one came up first as this could possibly be the culprit. However thereafter there were no codes coming up hence his suspicion that it was circuit related. I haven't had the car on diagnostics recently and I suspect it will once again give that whole list of errors.
AnswerIt sounds like you are in good hands with your mechanic. I would have suggested the same thing. Sometimes there are so many codes it's hard to sort them all out. However, I'm going to make a prediction that it is the MAF. Let me know what you find out.
