Why so much boost - 1.2 bar

[Pants]

Hi all,

Been punting the legnum around for a while now and noticed that the Defi boost gauge (has a peak, up, down and play button on a controller box wired in) is showing up to 1.2 bar.

This has been an issue as I think I have hit the fuel cut (violent loss of power, sort of judders is the best I can describe it) and the car stops going fast. Aside from the gauge leaking somewhere causing the high reading what else can cause that much boostage? There is no boost controller fitted that I can see and it has a hard piping kit and an aftermarket exhaust of some description. Leaking bov? Wastegates?

I have been keeping an eye on the gauge when driving, overtaking etc and as long as it doesnt boost past .9 bar there is no issue and it hauls as expected.

Cheers,

Rob

 

[snickells]

...are you saying that it's "hit" 1.2bar at some stage and the device has logged this as it's peak boost reading? Or, that your hitting 1.2bar all the time?

 

[Pants]

1.2 peak but If I put the foot to the floor it will boost above 1 bar all the time, all gears. Not mashing the pedal I can hold it below 1 bar and it is ok. It would be nice for it to not go above .7 - .9 regardless of how much throttle is applied.

 

[godzilla]

Hmmm, 17.4psi. Hard piping and an exhaust (especially if it is all the way from the turbo) will cause an increase in boost but not likely that much. Some cars came out with anywhere up to 11 or so psi from factory. You start modding from there and you will easy get up to a bar. Factor in load and very cool weather and you will be getting up there.

The shuddering and missing may be boost cut yes but could also be your plugs failing under high boost. Boost cut though is usually like hitting a brick wall, not progressive.

You need to take note of how and when it happens.

Oh and a leaking BOV won't cause boost cut. If it is leaking it will continue to leak and you will lose boost - not gain it.

 

[Guest]

Boost pressure is not reaching the wastegate actuators, or actuator(s) are not working.

 

[TME_Steve]

You may have issues other than hitting the fuel cut if you don't have other supporting mods....

Anyway, given you say "violent" and your gauge is reading 1.2 Bar and it's a defi not some cheap crap I'd say you are over boosting. Your 0.9 bar also correlates with JUST missing a boost cut.

So either you have some sort of boost controller in there, something blocking the lines to the wastegate(s) or broken lines to the watsegates(s) or a dud factory boost controller jammed open.

So a process of elimination, firstly check the pipe work for a boost controller unless you have already done that. Then I would bypass the factory controller and connect the wastegates directly to the manifold by disconnecting the hoses either side of the controller and joining them together. If you see 6 or so psi max you don't have a blockage and the controller is not working for whatever reason. If you still go past more than 6 or so then you have to check that the lines are not blocked or fallen off/split etc. If connecting directly fixes it you have a dud controller or the cables have falllen off it etc.

Hope this helps....

Another example of how fuel cuts are a wonderful safety measure and should be moved not disregarded....

 

[bradc]

Do you have any aftermarket boost control in the car at all?

 

[Pants]

No. I've read through the thread about installing a boost controller and there is nothing connected to the hoses. The boost gauge is connected to the vacuum line at the intake

 

[bradc]

Is the stock boost actuator there and plugged in?

 

[Pants]

where is that located? is there a photo somewhere?

 

[bradc]

Just in front of the throttle body at the same height

 

[Pants]

Looks all conected fine...

 

[TME_Steve]

Now you hve found it, do what I said....

 

[Pants]

Afternoon,

So on Sat and mate and I pulled the intake apart a bit to see if there was anything obviously wrong. All the tubes were connected and there were none that had obvious leaks.

The pic below is what I think happens - does it look right?

The red ended pipe is the one that gets tapped into for a MBC/EBC and it runs to a t-piece. One end goes somewhere (I think its the one to the wastegates?) and the other end goes to what I think is the factory boost controller? It has wires running into it and another tube runs to an intake pipe that is before the turbo (rear turbo?).

Cheers,

Rob

 

[TME_Steve]

That's it.... seized controller? Bleeding continuously???

 

[chrisssss]

wow 1.2 bar on our turbos have to say this is way too much ive pushed the limits on them at 16psi just to see what figures id get but i dumbed it back down to 1bar soo i dont kill them try to get a good bost controller and play with it ive found that differnt ecus hit fuel cut at differnt varients of boost. before my car was an auto i was only at .9 bar but now that it is manual i can stay on one bar all day everday no boost cut or fuel cut

 

[Pants]

Thanks for the reply Steve. So above you were saying bypass the t-piece that goes to the boost controller - how long should I drive around with it like that? I plan on bypassing the controller this Saturday (helping same mate un-defect his bike so two birds ) and if that's the issue chase up a new controller asap. Actually do I need the standard controller? Yes probably?

 

[Pants]

Win! Bypassed the factory controller altogether this afternoon with a $70 autobarn bleed valve. Closed it's holding .6 bar. Much happier now, i can just bury the right foot and not worry about anything Thanks for the help guys

 

[TME_Steve]

Yeah but now you only have wastegate pressure, so you're boost controller solenoid was jammed open.... You should fix that or just wind the bleed up to 10-11psi for factory boost or more if you want.... 14 or 15 will get you close to the boost cut. Glad it worked.

And Chrissss you can run 1.2 bar at lower revs with the correct supporting mods....