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Issues With Boost Sometimes Hitting Different Boost Levels

dori34

By dori34,
in Engines & Forced Induction

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dori34 Grand Master

dori34

Posted
Posted

got a bit of a weird problem, at first i thought it was coilpacks going on me due to misfire but it seems to be flat spot rather than misfire as i checked coilpacks (splitfires) and changes to new bcpr8e plugs

randomly when i give it, it would hit 9/10psi and in next gear it would only hit 5 or so psi.

using a turbosmart bleed valve with factory turbo.

can anyone suggest what may be the issue? i've been away from turbo cars for too long so i've checked the most basic things but then its beyond knowledge to further diagnose.

photo below of how the boost tee is setup, is this correct? it came with the car this way, i've only turned the boost turn as it was running 15psi before.

i've read the DIY thread but it seems the guys are getting the pressure source from the cooler pipe after the throttle body with the factory piping, mine doesn't have that

Note: the other line (that doesn't go to wastegate) is connected to the pressure source from the plenum, not throttle body. bottom hose of factory solonoid has been removed,

its probably something simple/silly that i just can't see

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2wqc0vd.png

GTSBoy Grand Master

GTSBoy

Posted
Posted

Bleed valve could have AIDS. Inconsistent boost is one of their trademarks anyway, but it shouldn't be that bad. Would tend to suggest that it's got something in it (a flake of paint or rubber or something) that is part of your boost control now, and sometimes opens up the flow path enough to stop working as a boost raiser.

GTSBoy Grand Master

GTSBoy

Posted
Posted

OK, for some reason half your initial post wasn't there when I first answered, and there's no sign that you edited it either. Weird. Anyway, having now seen more text and your photos (not that the photos are that helpful, but they do raise some questions)...I think you might have a problem because of the way it is set up.

The boost source for the actuator itself, which in this case is the only boost source connected to your boost controller*, MUST come from the turbo outlet. Either right on the compressor housing (like it is on R32s) or off the hot side intercooler pipe, as close as possible to the turbo outlet itself (like it is on later Skylines). Sure, it can actually come from anywhere upstream of the throttlebody, but let's ignore that and agree that the turbo outlet is the correct place.

IF the boost source for your bleeder is taken from the plenum, you can get really weird results. This is because the plenum's pressure is more or less controlled by your right foot. If that signal is then being fed to the boost controller and then the wastegate, then the wastegate will do lots of opening and closing that it doesn't necessarily need to.

In your photo, those hard lines that run along next to the crossover pipe are not intended to be used for supplying boost signals to anything. They are originally for the charcoal canister. Don't use them for boost control. Especially don't use them for a bleeder.

*You may hear of people correctly taking a boost signal for a boost controller from the plenum. This is necessary for an electronic boost controller that measures the plenum pressure to display on the front panel. It's not directly used for control in most such EBCs. it's really just for information and for setting up the controller. The actual boost signal that is fed to the wastegate is STILL taken from the compressor outlet on EBCs, just like a bleeder.

dori34 Grand Master

dori34

Posted
  • Author
Posted

So I replaced the turbosmart bleeder with a turbo xs one, 7psi sweet, 9psi sweet. Will try 10psi like how turbosmart was and go from there.

So far so good. Same issue as this chap on r31 forums

http://forum.r31skylineclub.com/?topic=31879.0

scotty nm35 Grand Master

scotty nm35

Posted
Posted

The turbosmart T's have a smaller hole than most others, for the VQ25 I prefer the Turbosmart, but many have had issues using them on RB's.

The best option is a stiffer spring in the actuator, as close to your desired boost as possible, then bump it up a little from there if required.

dori34 Grand Master

dori34

Posted
  • Author
Posted

i am writing off the turbosmart bleeder as crap, no issues with the turboXS.

I even tried with my mates spare turbosmart bleeder with exact same issues.

However i will tap a nipple into the cold pipe as that is best place to get the pressure source from.

7psi never felt so fun. :D

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