VW Passat TDi Turbo cutting out at high speed
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I have a 1996 VW Passat 1.9 TDi Estate (engine type 1Z (european))which loses turbo power at 
the high pressure end -between 2500 and 3000 rpm, usually when accellerating at speed of 70 
Mph in 4th or 5th gear. 
 
Once the power drop off is experinced the power loss (ie lack of turbo) continues through the 
driving range until the car is stopped and restarted. Once restarted the turbo power is restored 
until high revs are reached and the whole cycle of power loss is repeated.  
 
I wondered if it could be the N 75 valve as switching off the ignition and restarting appears to 
reset somthing -perhaps the solenoid?  I have checked hoses for leaks. The BOSCH Man 
reported one fault from the ECU but no detail as to the cause of the problem. Car drives ok as 
long as revs are kept down below 2500. Another thought is too much fuel? Has anyone 
experinced a similar problem ? Any ideas and advice welcomed! Thanks for reading this..... 
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Hi 
There are two main items which can cause this. 
The airflow meter is prone to problems and the other is the turbo pressure control valve. 
Can you check boost pressure ? 
If you have a gauge check boost pressure under load ( while driving) You should get a boost 
reading of 1-1.2 bar. 
Have you had fault codes read? 
What codes were there? 
The only other item which i have had problems with is the turbo. 
Do you get black smoke when you loose power? 
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I have had this fault and it was the charge pressure control valve bolted to the bulkhead a bit dear 
but it sorted it out . If you pull the multiplug off the air massmeter and the power is better allthe 
time then the meter is at fault as it goes into a default mode........hope this helps
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Dave and Phil, 
 
Thanks for your advice.  
 
Dave,  
I'm not getting black smoke, so Turbo should be ok, hopefully. I'll get the boost pressure checked 
under load and get the fault codes read. Although the BOSCH guy did the diagnostics check, he 
did'nt indicate any codes. 
 
Phil, 
I'll experiment with the multiplug on the air massmeter and see. If this is the case I presume i'll 
need to replace the mass meter (ie the MAF made by Pierburg?). 
 
Also can you confirm the charge pressure control valve is the same thing as the N 75 valve - the 
gadget with the blue and red tubes goining into it, located near the ECU near the windscreen wiper 
housing? 
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Hi, Follow the pipes there are two valves that look the same the one you need has a pipe that goes 
to the turbocharger body, this valve when faulty can reset itself when ignition is turned off the on....
...A defective air mass meter does not record any faults in the memory you have to look at 
performance figures using a boost guage.
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It's fixed! Full pwer is restored and car drives like new. I replaced the changeover valve 
(VW part No: 028 906 283 F. ( 37.00 less Vat) also called a N-75 or Pressure boost 
Valve /solenoid......) and cleaned throught he 3 pipes which lead to it using surgical spirit and 
Carburetta cleaner. I fixed the pipes at one end using VW Oetiker clamps and acro ties at the other 
end. 
 
Thaks to every one who helped with this problem. 

 



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