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Discussion Starter · #1 ·
Right, I've done a quick search on this but can't find anything particularly definitive.

Symptoms:

The boost levels surge and drop whilst using heavy throttle between 2500 - 4000 rpm.

If I floor it from relatively low revs, the boost never comes on to full (19psi). It always levels out at around 12psi, yet if I apply the throttle gradually whilst accelarating the boost peaks at 19psi when the throttle is wide open and the engine is above 4000rpm as it should.

Am I going to have to bite the bullet and get a forge actuator (mine is the standard unit with a slave spring) or is it a question of ditching the APC and going for an MBC? Or both maybe?

Driving me mad it is!

Oh, new plugs a short time ago (about 2000 miles) and I only use Optimax.

Ta. :D
 

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That sounds pretty similar to my symptoms, so I'll be watching with interest ;) I also find that when I get peak boost, say in 5th gear if I build gradually to WOT, it does pulse a little, by about a couple of PSI, with about a 1Hz frequency. Does yours?
 

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that is how it works - boost floats at peak. it goes up then gets kicked back at the limit and then tries to reach it again.

if you want your boost to be steady, get yourself a electronic boost management system with their APC valve which can be configured from the car. Various settings there and boost goes up faster as well.
 

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There is always a certain amount of float in boost levels, especially as you described at mid-range rpms w/ WOT. Issue of whether it is excessive is difficult, if wildly fluctuating and gas/plugs/DI can be ruled out a weak actuator is the likely suspect. I get the same symptoms as well.


Actual raw level of boost is not as important, as temp and many other variables have an impact. Key is the torque and HP it puts out.
 
G

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Discussion Starter · #7 ·
Thanks guys.

Diverter valve? Not familiar with this, however I think the actuator has to go as it is an assisted stock one.

I'll do that first since it's only 100 notes.

I will report my findings back. Thanks again.

:D
 

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imo it will be floating no matter what you do at the max boost unless you have an electronically managable APC valve.
 

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what car do you drive ? isn,t 19psi rather high i thought the cut off would have occurred by then.

i just read elsewhere on here that fuel cut off occurs at about 15 psi on a full pressure turbo. it is a question i,ve wanted answered ie how high can i safely set the boost on a 2.3 fpt ???

:roll:
 
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