MissFire then loss of Power.

BARRIE

Member
I regularly commute 50miles on what is probably the worst main road in the UK-- the A147 Ipswich to Norwich. There is a 50mph limit over 90% of the journey and only one four mile stretch of dual carriageway where one can overtake the heavy lorries. A problem that has developed over the last three weeks is that at about 80mph and accelerating there is a slight hiccup followed by a loss of power and slowing down to about 50mph. I have tried slowing to 30ish then accelerating again but my 1.4tdi wont struggle past about 50mph. After stopping and resting for a few minutes then restarting everything is back to normal except that the hiccup and power loss re-occur at about 80mph.
I thought maybe it needs a squirt of carb cleaner in the maf senser but as far as I can see it needs a major stripdown to get anywhere near the maf senser- assuming I am searching in the right place (bottom left hand corner under the headlight when facing the engine?).
I will be eternally grateful if anyone can suggest what the problem might be and how to cure it.
 
Hi Barrie

You really need a scan even if the engine light isn't illuminated - even then you may not know exactly what is wrong. I have almost exactly the same problem on our A6 and the scan shows an N75 valve fault. which is the diverter valve (dump valve by any other name only it doesn't dump it recirclulates excess turbo pressure). Only it isn't as i've changed it with others known to be working twice!! I'm currently going through all the vacuum hoses and the the high pressure hoses feeding the inlet in a systematic way. Then it will be inline valves. Like Spike says, i'm hoping mine is just a split/loose hose but it could be damned difficult to spot.

Cheers

Jonathan
 
Thanks for the advice, Spike and Jonathon. I will have a poke around at the hoses and then get a scan if I cant find anything. My 1.4Tdi is still under warranty ( an Insurance type warranty issued by the Dealer) and I very much expect that the diagnosis of the problem will not be covered.
Thanks, Barrie
 
Further to previous comment, I had a look and feel of the turbo pipework but could not see any problems. I therefore commissioned a scan with Ipswich Audi main dealer under warranty and they promptly dealt with the problem.
The mechanics written comments are as follows:
' Fault with Turbo Charge Pressure Control Solenoid N75--carry out test plans and check Turbo Boost Pressure using measure value Bucks on VAS5051B. On Road Test over boosting causing car to shut turbo down--return to workshop and using vacuum pump test charge pressuere control solenoid--solenoid ok-- check turbo actuator ok--check vacuum pipe to back of turbo--no vacuum-- trace vacuum pipe and found to be broken--repair and retest-ok'.
Hence your diagnosis re possible faults in pipework around turbo was on the nail. The car now goes as it should do but I expect that fuel consumption will suffer now that I have got a turbo again!
PS This work was carried out under insurance warranty and Audi charged £167 inc VAT.
Thanks very much for your help.
 
Glad you got it sorted eventually and reasonably cheaply (compared to what the cost could have been).

Thanks for letting us know too - all adds to the collective knowledge.

Cheers,

Mike
 
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