Manifold Vacuum

[peeeot]

I've tried taking a vac. reading from one of those hoses on top before and it was very low. I think I used the large hose. If I take a reading at the vacuum canister under the fender, I get a steady 18. If I were you I'd try someplace else just to make sure.

 

Also, if you're calibrated for more boost than the factory would have provided, then it makes sense that your turbo could be lowering manifold vacuum by way of boosting air flow into the manifold, perhaps even at idle. I don't know for sure, turbos are out of my realm of experience.

[Guest TurboSedan]

I've tried taking a vac. reading from one of those hoses on top before and it was very low. I think I used the large hose. If I take a reading at the vacuum canister under the fender, I get a steady 18. If I were you I'd try someplace else just to make sure.

 

actually, the line i used was fine, not to mention it's actually the very same line that goes to the vacuum canister under the fender. you got a really low reading because you used the line for the canister purge solenoid (the big line). if you disassemble the throttle body and look inside you'll see there are different passages going to the different ports on top of the TB. i think the ports for CP solenoid & vacuum EGR are right inline with the throttle blade when it's closed, which would result in the low vacuum reading you got. this presumeably lets the CP solenoid and vacuum EGR know when the throttle plate opens.

 

Also, if you're calibrated for more boost than the factory would have provided, then it makes sense that your turbo could be lowering manifold vacuum by way of boosting air flow into the manifold, perhaps even at idle. I don't know for sure, turbos are out of my realm of experience.

 

it wouldn't make a difference at idle at all, regardless of my boost setting. the compressor isn't going to start pushing enough air to start pressurizing the intake manifold until the turbine starts spinning fast enough - IOW enough engine load to spool the turbo.