On a 96 A4 1.8t, what reads/measures the boost pressure ? I understand that the n75 valve regulates the pressure to the wastegate via the ecu/electrontic plug, but what sends the boost pressure reading to the ECU? I don't believe that there is a manifold absolute pressure sensor on this year of car. where does the ecu get its actual vs requested boost reading from ?

 

It might be the diverter valve. The ECU also uses the MAF sensor
to determine the amount of air in the intake.

 

i believe it would also be the n75.

 

The map sends the actual to the ecu. Since the AEB doesnt have one, its all dependent on the g/s value of the maf

 

^^ there you go

 

Sorry, what is the 'g/s' value ?

 

does th n75 'read' boost pressure ?

 

grams/sec (wrote the wrong thing in PM)

n75 bleeds off boost pressure, not read it. Its just a dump boost controller

 

Thats what I thought as regards the N75. So there is nothing that reads actual boost pressure on a AEB engine ?

 

no, thats why you need to run a maf and a boost gauge. Not sure why this is such a big deal for you, the maf and o2 sensor do a good job at regulating a/f. Its not as good as the newer ecu's that have a wideband o2 and map, but there are still A4's running around with 1000cc tunes from Tapp/eurodyne on a gt35r and making great power.