Confusing Boost Gauge Readings

[Guest]

Looking for some guidance here, have installed a boost gauge and it is reading vacuum the majority of the time, even under boost. I'll be honest my experience is limited but this doesn't seem right. Car is currently running stock boost. So a bit more info on approx gauge readings:

Ignition Off: zero
Idle: -20 inHg
Driving Off Boost: -10 inHg
Normal driving (changes at 4000 - 5000 rpm ie under boost): up to zero or 1 psi
Hard accelaration in higher gear (peak boost): 7-8psi

Gauge is an Autometer and in gwc (confirmed by previous owner). I have had another gauge previously installed that showed similar readings, though it was the gauge at fault.

Line is plumbed in to line at front of plenum, teed off between plenum and FPR as recommended in other posts http://i98.photobucket.com/albums/l275/ussapper_00/absolute_plenum_pressure_line.jpg

I have also tried teeing off from line to rear of plenum http://ozvr4.com/forums/attachment.php?attachmentid=3325&d=1247046890 as others have recommended with the same results.

Stock BOV has been replaced with Sard R2D2 and whilst holding boost a lot better has made little other difference to gauge reading behaviour. It does however make it easy to tell when boost has built up!

Car appears to be behaving normally and goes well enough, but the fact that two different gauges each plumbed in two different locations are showing the same readings is concerning me that something is wrong? Have checked all hoses etc for leaks and nothing is apparent.

Any ideas greatly appreciated....

 

[OVR444]

Sent you a PM about this mate;

Also make sure there is no kinks in the vacuum line.

Basically a boost gauge will show neg boost pressure when the car is idle or cruising along. When you put your foot down the turbo spools up to 0psi (which is then "boosting"). Anything past 0psi is boost pressure; and when you back off the accelerator it will open the BOV which will vent your boost pressure sending you back to a negative value again, until you put your foot down to begin the cycle over. Mine sits on -10 to -14 normally depending on gear and load; its only when I lightly touch the accelerator the turbo's will start spooling back to 0psi or boosting over again.

I hope that made some sense...


This sounds normal for a turbo car; would you say its similar to this video?

(notice when he rev's the engine it will only spike up to 0 psi as a bleep of the throttle won't be enough to make boost.)

Note: You would certainly know if you weren't holding boost; as it would feel like a regular N/A car with no BOV venting on back-off.

 

[Guest]

Brett, from what you have posted here looks like normal behaviour then, just me being a bit green and cautious before I start winding things up! Thanks for the info

 

[snickells]

Thats all normal.

 

[Guest]

Cheers Steve - maybe we should change the thread to normal boost gauge readings!

 

[happymatch]

well, got one question to ask, when i accelerate, my boost gauge goes up to about 12psi ( i have set to that). the boost goes up then it bounces down and up a lot. i.e, paddle to the floor, boost goes up to 12psi, then down to 8 psi. does it mean boost leak? or normal?

 

[OVR444]

well, got one question to ask, when i accelerate, my boost gauge goes up to about 12psi ( i have set to that). the boost goes up then it bounces down and up a lot. i.e, paddle to the floor, boost goes up to 12psi, then down to 8 psi. does it mean boost leak? or normal?

Sounds like a boost leak to me my friend. Do you have a MBC or EBC? If its happening towards redline; like a tapering off kind of thing that could be normal for a manual controller.

But if you say its violently spiking up and down then you have a leak somewhere. So I would check bov, vacuum lines, vacuum lines to gauge etc.

Perhaps lower your boost back to the 8-9 and see if the same thing happens; if not, then you know you might have a leaky bov.

Are you seeing something similar to this under WOT

http://www.youtube.com/watch?v=mpHKd66Xr-4