hi i have a b5.5 wax with 200k on and i was getting an over boost fault and couldn't find the fault and put it down to the vnt in the turbo then it suddenly started using loads of oil so i got a reconditioned turbo from midland turbos and it is spot on now and not using any oil and drives better than ever apart from one thing with the cruse control set at 70ish on the motorway i keep getting limp mode and a fault code boost pressure negative deviation (so under boost)
it only seems to do it under very gentle acceleration on a very slight prolonged incline at around 70 mph
on idle the actual and requested boost is 14psi
under very hard acceleration and flat out in 5th gear the the requested is 35pst and the actual goes up to 37psi and settles at about 35-36 psi as the speed increases
at 70 under light acceleration the requested is about 28 psi and the actual is 25-26psi but if you press the throttle slightly the actual; ors up to about the same value as the requested boost
iv fitted a new Bosch air max meter and can't see any boost leaks so what could the cause be (boost pressure sensor many)
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help b5.5 awx under-boost
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