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So I was wondering if you guys from the forums could help me with a bit of a problem...

I installed a new Boost Controller on my car, it's a manual controller by GReddy. And I installed a Boost Gauge. NOW...

I have the boost at like 10-12 never more than that, and I began to notice something. Every now and again when I full throttle my car, boost goes up and RPM's go up, and then... the car sorta... jumps. Almost as if the car stops and then keeps going... it's jumpy to say the least.

Now it doesn't do that when I build boost evenly, only when I suddenly full throttle. So my question is... What could be doing that?

Nismo came up with the theory that it was the spark plugs, and it makes some sense, seeing as how a raise in boost might lead the engine to need colder plugs wouldn't it?

I also have a bit of a vacuum leak, but I'm not sure that it's the problem. It might be who knows... so can you guys help please?

Keep in mind that I changed my plugs about 4 months ago... so they're not that old.

$20 says it's your clutch telling you it's got a few months left, slipping for a split second. Mine started doing the same damn thing 4 months before it started slipping definitively.

It feels like the car just stops accelerating for a second, and then shoves you back into the seat as boost peaks, right?

Couldn't this be a culprit of boost cut maybe?

This sound like 2 problems in one....

If your revs are jumping, then it is most probably your clutch slipping.....

As for the boost going up, sounds like you have boost creep.... do you have a de-cat or aftermarket exhaust?

Also, could be a badly set up boost controller, or an old wastegate actuator....

Also worth cheking you plugs..... and just to make sure, you are using high octane petrol right?

Nope, it would be a lot more than a split second. That, and 12psi is stock WG pressure, he'd have to boost up to at least 15psi to hit cut.

Revs don't jump at this stage, the drivetrain just stops responding for a split second, which actually causes a very slight drop. You'll have to see major high boost slippage before the clutch'll let go and let the engine free-rev. Trust me, I just went through this.

An MBC is going to lessen boost creep compared to the stock BCS.

Plugs wouldn't be just when he hits full boost, but at any time while he's there.

Its boost cut, when he smashes on it. the mbc causes a boost spike and it hits boost cut. if you roll into it the boost will build slower and its not going spike as bad.

You mean fuel cut?

Cyrus, how high is your boost spiking?

fuel cut/boost cut are one in the same....

The boost actually doesn't spike or doesn't seem to. It's when I full throttle that the car sorta kicks back and then speeds up... it's weird.

I DID contemplate the clutch... since I have no idea when the clutch was changed. It could be that since Nismo had the issue when his was slipping under boost. This one might be valid.

The boost seems to do it maybe 2 or 3 times and them continue boosting, with no problems whatsoever.

When it does it's maybe 2-3 PSI. Any suggestions?

im in the 3000 as of right now, it isnt the clutch, thats for certain, I think its the plugs because when i drove it it still missfires in higher boost weather i slowly accelerate or wot, its just worse and more noticible under wot

So since I changed my plugs my car doesn't go stupid anymore.. but I have a vacuum leak somewhere. I can tell by my gauge. It goes down to 25 vacuum and then creeps up to like 19 ish... is this regular? I doubt it..

We need to find you a smoke machine and we could solve that problem in 5 seconds.

Build a boost leak tester and cover your intake piping and vacuum lines with soapy water. That'll make things dead obvious, too.

And when specifically does the gauge do this, when you clutch in? If so, I should certainly hope it becomes more ambient when switching from engine braking to idle...

This post has been edited by cmspaz on Feb 24 2009, 06:52 PM

No need to thank me

Well it does it when I engine brake.

For example let go of the throttle with it still in gear, or simply throw it into neutral, but when I throw it into neutral it does the same thing but less. Then after about a second it jumps back up before 20...

How do I do it with the soapy water n stuff? Or build a boost leak tester?

that is normal for the vac to drop like that when you engine brake.

Yeah, sounds normal to me, as the engine cycles down the system should naturally become more ambient.

Boost leak tester: http://www.vfaq.com/mods/ICtester.html

It says to listen for leaks, but most people will mix up some soapy water and pour it over all of the intake piping. When you pressurize the intake, the air coming out will cause the soap to create bubbles, make the exact location obvious.

Lol, so thats what he was talking about Of course its normal for the vacuum to drop really low when engine braking

Actually I told him to change the plugs before he even posted as for the car, its running fine, I used it today and it boosts and idles normal this whole vaccum leak thing is just in cyrus' head, he's a weirdo like that.

Ok so I'm the weirdo huh?

So tell me why I hear a "hisssssssssssss" after I turn the car off... hmmmm?! Am I going mad THEN!? Cuz you heard it too!

is it that ball bearing turbo spooling down?

I'm not sure... because it didn't always make that noise...

Does it last for a while? If so, my ex's 1.8T Passat made the same noise. We never figured out what it was.

It does it for like... maybe 10 seconds after the car is turned off.

When the car is on you can STILL hear it... I'm contemplating just taking all the pipes out and tightening em back up..

This is causing issues! I turn up the boost on my boost controller and it's stuck at 6... it won't go past 6... it's good, yes. But it sucks how I can't go higher!

if the boost wont go past 6lbs even if you raise it on the controller its most likely a boost leak. My tester wont work on your car though, try to get your hands on one that does, ill look too.