Boost gauge bouncing at full boost.

[DROPthatCLUTCH]

So I was out tuning a little today and noticed once I hit full boost (15 psi) it would bounce down to about 12-13 and go back up to 15.

It did it fast and kept bouncing until I was off the gas.

 

[TsiJohn333]

Sounds like a case of boost creep

 

[razrman8]

I noticed in your profile that you are running an Evo316g. These turbo's are notorious for boost creep. If you are uncertain of what boost creep is, a simple search will tell you all that you need to know. I also noticed your manifold and cat-delete. Is that all on stock exhaust? If not, that would be another reason to lean towards creep.

In a lot of cases 'boost creep' can be tamed or eliminated by doing some porting to your turbo. There are quite a few threads on that as well.

 

[DROPthatCLUTCH]

Hmm.. Weird. Never done it before... Also weird because, doesn't boost usually creep up? Not down?

And, yes. Stock exhaust. I've ported a 14b before. Maybe I'll find some time for a port job soon.

 

[razrman8]

You say it has never done it before, have you changed anything recently? If it is going up to 15psi and then settling down to 12-13, that would be referred to a boost "spike''.

 

[DROPthatCLUTCH]

Just put my 680's in last week. That's why I was tuning.

But I'm not rolling with 12 psi. My boost is set at 15. It's actually dropping a couple psi, THEN, bounces back up to my set boost pressure, then continues to bounce down and up from 13-15 until I'm off the gas.

Almost like the wastgate is opening and closeing.

 

[razrman8]

It is usually suggested that if you are to even incounter a boosting problem, that the first part of your issue diagnosis be a proper boost leak test. Have you done this?

 

[DROPthatCLUTCH]

Yes, that is very true. I had it in my garage yesterday and did blt, and fixed the leak that I found where the uicp connects to the ic. checked every other spot and found nothing, other than the tool leaking boost... But I fixed that also.

But that was yesterday, and something might have happened during one of my pulls, so tomorrow after work = blt time again.

If thats not the issue, could a pre-turbo exhaust leak cause this? Just brain-storming here. Bare with me.

 

[razrman8]

Did you use soapy water to perform your test? From what I am gathering you are saying you have got "jumping boost". Does the car cutout? Sputter?

 

[gusu]

Are you losing power as you loose boost or is it staying the same?

Also I had a problem with this before. It ended up being I needed to use a stiffer line to my boost gauge. My old one would balloon then loose boost and expand again, it would do this after about 14 PSI.

 

[DROPthatCLUTCH]

Lol of course I used soapy water man!

Nope, it just pretty much continues boosting..

Damn, I hate these mystery problems.

How about this, I'll get home from work tomorrow, BLT, then I'll go out, do a couple pulls and see if it's still happening.

I'm pretty sure my IC was heatsoaked today when this was happening too. I started to get random knock in places that I already corrected, and my UICP felt really hot.

Are you losing power as you loose boost or is it staying the same?

Also I had a problem with this before. It ended up being I needed to use a stiffer line to my boost gauge. My old one would balloon then loose boost and expand again, it would do this after about 14 PSI.

Hmm. Well, I happen to have some stiff vacuum line in my garage right now.
The line that I'm using is pretty soft, just that it's never showed a problem before.
I'll change the gauge line, and the MBC lines tomorrow also.

Edit: I just measured, and I have about 4 1/5 ft of vac line. Think it'll reach from the T to the center vent?

 

[ajinvista]

Yes, that is very true. I had it in my garage yesterday and did blt, and fixed the leak that I found where the uicp connects to the ic. checked every other spot and found nothing, other than the tool leaking boost... But I fixed that also.

But that was yesterday, and something might have happened during one of my pulls, so tomorrow after work = blt time again.

If thats not the issue, could a pre-turbo exhaust leak cause this? Just brain-storming here. Bare with me.

Mine usually does that when my exhaust manifold need a tightening, or the turbo mani bolts. My boost guage flutters around 20psi when this happens.

 

[PieEyedPiper]

If you just installed your 680's, it's likely to be that. Or a leak.

 

[DROPthatCLUTCH]

Okay, I'll crank those down when I get the chance. And if the problem still exists, I'll change the gauge vacuum line.

 

[PieEyedPiper]

Okay, I'll crank those down when I get the chance. And if the problem still exists, I'll change the gauge vacuum line.

Well "cranking them down" might not be your issue. However, tuning for them could be. Especially if you're using an SAFC. 680's are pretty much the limit for an SAFC and tuning for them can be more than challenging.

 

[DROPthatCLUTCH]

What are you talking about? I'm talking about this.

Mine usually does that when my exhaust manifold need a tightening, or the turbo mani bolts. My boost guage flutters around 20psi when this happens.

PieEyedPiper, are you saying that the tune is causing the problem?

 

[PieEyedPiper]

What are you talking about? I'm talking about this.



PieEyedPiper, are you saying that the tune is causing the problem?

Yes.

But don't misunderstand, it could very well be a boost leak, a loose connector or even an old vac. line leading to your boost gauge. But it's helpful to look at car problems with a similar attitude to "What has changed from then to now?". In your case, nothing except for your injectors. All of a sudden the injectors look like likely culprits since you're using an SAFC to tune them and SAFC's are notorious for barely being able to tame the 680's.

Just to be clear, what other symptoms are you experiencing? Do you have a logger? Have you inspected your plugs/wires?

 

[ZenkaiRacerDsM]

Ever figure this problem out? Do you have an external wastegate? Mine does the same thing at any boost level higher then my wastegate spring pressure.

I think its because I have an electronic boost controller hooked up to the gate in the same way I would have a manual boost controller hooked to it. So since I dont have a pressure source on top and bottom of the wastegate the valve on the gate is just bouncing up and down.

I just need to find my other wastegate banjo fitting to install it the other way and see if it stops.