Discussions with a diesel mechanic yesterday (Re EGR removal) indicated that
on the 2002 model the boost is unable to be adjusted. After reading several posts here I am more than a little confused. Did I misunderstand or is he right?
Mine is a 2000 model so not a big difference between your zd30 and mine. To put it very simply, if you block the the EGR the spool up rate of the turbo may quicken, this can result in boost spiking higher than normal (and on some trucks, limp mode).
The boost is adjustable in a couple of ways,
1 being the fitment of a Dawes valve system where adjustment of the spring that seats the ball causes boost to be bled back into the vacuum line reducing vac to the VNT.
2 being fitting a needle valve in the vacuum side of the Dawes valve, this allows normal atmospheric air pressure to bleed into the vac line and again can reduce spikes and boost.
3 being directly at the adjustment thread below the VNT actuator.
He is quite possibly referring to a waste gate type system which is not on our vehicles.
