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1.6 tdci 2010 overboost vacuum

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hi all i have a boost problem p0234 what i could do with finding out is ,does anyone know what vacuum should be., At tick over i have 0.8 showing ,if i rev to 3000 it drops to 0.4  and 0.2 at 4000,, should it drop to nothing to void overboost ,i have a boost pressure regulator to fit if required ,the vac gauge holds 0.8 when engine stops and ignition is switched off it does however drop to zero when i hear something click ,i can drive around for days and no red light but when the missus gets in and drives its showing within a couple of miles ,guessing she has bigger foot than me if you know what i mean

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3 hours ago, hotboxcharlie said:

At tick over i have 0.8 showing ,if i rev to 3000 it drops to 0.4  and 0.2 at 4000,,

Where were these vacuum pressures read?

The vacuum on a diesel is generated by a pump, and is used by the brake servo and turbo actuator. The vacuum at the pump inlet should be good (probably <0.2 bar abs) at all times with the engine running. The vacuum at the actuator will vary with power demand, as the Turbo is brought in. Though the turbo is not used much when revving in neutral, only when the engine is working hard.

I think the 1.6TDCI turbo actuator is normally in full boost state (engine off), and vacuum is applied to the actuator to put it into minimum boost state as soon as the engine starts. Then as engine load increases the solenoid valve (or pressure regulator) is used to reduce the vacuum (increase pressure) to ramp the turbo up.

So poor vacuum (0.8 bar abs) at idle might indicate a problem with the vacuum pump or system. Checking vacuum at the pump or brake servo could check this.

The other problem is that if your gauge is reading in negative bar gauge, rather than positive bar absolute, then your measurements effectively reverse, with 0.8 being a good vacuum (0.2 bar abs), and 0.2 being poor vacuum (0.8 bar abs). Units are rather important!

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thanks for your reply Peter the vacuum reading is indeed in a minus value as taken at the actuator on the turbo ,so the reading at tickover is -0.8 then reving to 3000 at standstill it drops to -0.4 then 4000 is -0.2 i wasnt sure if the boost pressure valve should stop all vacuum ,im new to turbo although ive been a ford man for 50 years and worked on many ,my main concern is stopping the overboost my next job will be to clean and check the pressure regulator  when my body lets me get underneath the car,  if anyone else has any input that may help i would be grateful

Edited by hotboxcharlie
miss spelling
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