Excessively high boost or broken gauge?

[97gsxturbo97]

I dont know how long my car has been doing this or if it always has been doing this since Ive only had it for 3 months and just started driving it. The car has a stock t25, and stock BCS. The only modification are hard upper and lower intercooler pipes, k&n filter, and massive 3 inch downpipe with 3 inch exhaust out the back. I noticed at the track that the boost gauge was maxing out. It goes up to 20 psi. That cant be right. I know 3 inch exhaust will cause boost creep but massive boost spike? WOuldnt I blow something up. Also at times when the gauge is maxing out I can hear something like air or buzzing coming from the boost gauge itself. The only thing that I recently touched was the intake assembly but made sure everything is plugged in and tight as it can be 10 times. I also checked all the intercooler pipes and its all tight. This wouldnt be a boost leak right?

To compare I did a log with dsm link and there is no knock during a pull. I would imagine at 20+ psi on stock fuel that I would be knocking significantly and running out of fuel. Dsm link also has a boost est that climbs up to 17 by 5500 rpm and then decreases down to less than 10 by 7000 rpm.

The boost gauge is hooked up to the FPS at the intake source not on the line that the regulator uses. I recently pulled the vacuum line off the FPS to check the fuel pressure. I noticed when I took the line off there was air coming out of the FPS. That is suppose to happen I assume? It also takes a few seconds longer than normal to crank the engine over at times? Do you think this all could be related? Thanks for your help guys. Sorry for making this so long but I want to make sure I check all the variables.

 

[snowborder714]

What does your boost gauge read with the car turned off?
You can always take an air compressor and set it at 10 psi (or whatever you choose) and see how the gauge reacts to that pressure.
Did you put teflon tape on the threads of the nipple (that the vacuum line connects to)? If not, I'd recommend doing so.

And since you have DSMlink, you don't ever need to remove that vacuum line again. You can just turn the car to ON (don't start it), fire up DSMlink, and turn on the fuel pump via ECU > Miscellaneous.

 

[97gsxturbo97]

The gauge reads zero with the car off. At idle it reads -18 to -20 vacuum. Im going to recheck all the connections again. I dont even know the brand of the gauge it looks like a cheapo. My main concern is that the car is not really boosting 20+psi.

 

[snowborder714]

I'd say your boost gauge works fine.

Try running a vacuum hose from the nipple on the compressor housing to the nipple on the wastegate. This will cause you to run just off the wastegate's pressure, which will be around 11 psi (give or take a few).

 

[Auto RS T]

Let's start where Brian suggested and check the boost gauge first. Do it his way by checking the pressure side of things with an air compressor, or hook up a handheld vacuum pump with a gauge to your boost gauge and try to pull some vacuum. The gauges should match.

You can also check the FPR Solenoid with a vacuum pump.

Disconnect the vacuum line from the intake and hook the vacuum pump up to the other nipple under the electrical harness.

Unplug the electrical harness.

With the intake nipple open it should leak

If you plug the nipple and try to pull vacuum, it should hold

Now, If you apply battery voltage to the solenoid (positive to one side, negative to the other) and leave the nipple to the intake open, it should hold vacuum, otherwise replace.

 

[GofaST4life]

i had this same problem with my car...i could never figure out why it was over boosting...so i got a MBC and that fixed the problem. Still dont know why it was doing that though.

 

[97gsxturbo97]

Ok I just went over everything again. I took apart the intake and made sure every hose/clamp was perfect. No problems there. So then I move onto the boost gauge. I checked all the hose at the fuel pressure solenoid and everythings tight. I checked all the hoses at the boost gauge connection and everything is good. So then I took apart the boost gauge and everything is tight. I did however notice that the gauge does not sit at zero when off. It is on one tickmark lower than zero. So I take the car for a test drive. 2nd gear I punched it, gauge maxes out instantly. I put it in third and goose it to half or slightly over half throttle at low rpm. The gauge instantly hits 17 psi. There is now way a t25 can do this. Im betting the gauge is broken cause I swear it use to stop at 10-12 psi.

 

[97gsxturbo97]

The only other thing that I can think of was that I was playing around with DSM link when you can activate various solenoids such as FPS and BCS. Is it possible that something may have happened? Also can I use dsm link to test these solenoids. I do not have acces to an air compressor that I can adjust nor do I have a vacuum pump.

 

[Auto RS T]

You can bypass the BCS by doing what Brain suggested in post #4. It's not a test, but you can eliminate it as a probelm.

Its sounds like link just supplies the voltage to power the FPR solenoid. You can verify that with a test light or voltmeter. You will still need a vacuum pump to see if it will hold.

 

[97gsxturbo97]

If I do this and boost returns to normal then the BCS is the problem correct?

 

[snowborder714]

If you do as I said in post #4, and you boost to 11 psi or so, then yes, I'd say your BSC is the problem. You could either leave it like this or get an MBC and install it.

 

[97gsxturbo97]

It ended up being the gauge. I put another one on and everything was normal. There was definately something moving around in the old gauge so something broke. This is such a relief. I feared that I damaged something running over 20+ psi at the track. Luckily that wasnt the case. Thanks guys for your help.

 

[snowborder714]

No problem! Glad to hear it was just the gauge.

Go and mark this thread resolved

 

[KevinBoosted]

my t-25 was doing the same thing to me for months. i would always spike at 20/21 psi. it wasnt right. i finally put a hallman mbc on and now im boosting 14psi just fine

 

[97gsxturbo97]

Ok so I was so happy that I thought I found the problem. When I installed the new gauge I just tightened the fittings by hand. I went out and punched it and it stopped at 15 psi. I thought it was all good but I also noticed that now the vacuum never read below -10. Anyways the wires for the light broke and I returned it and got another one. I installed another gauge and now the vac is at -18 where its suppose to be. So a day later Im on the highway and I decide to punch it. I instantly hit 22 psi, I now know that since this gauge goes up to 30 unlike the old one which only went up to 20 psi. So I took off the vac lines running to the turbo and ran a line directly from the turbo to the wastegate. The bcs is no longer connected. Thats what Im suppose to do right? Now the boost never goes above 15 psi. It hits about 15 then tapers down a few psi. I have 3 inch exhaust on a t25 so I assume that normal. How can a BCS go bad? What is the point of having one if the wastegate will maintain control? Also can I leave this connected like this or will I damage something? Why wasnt I knocking at 22 PSI with a stock fuel system? What kind of damage could I have caused? I cant believe I ran it at the track like this. Thanks for your input guys.

 

[snowborder714]

That sounds about right for the boost level. You will not have any problems if you leave the setup like this. Then once you get an MBC, you can install it inline there. I'm not sure what would cause one to go bad, nor why you didn't hit fuel cut or experience knock at that boost level.

Here's what wikipedia says about a BCS:

In effect, a boost-control solenoid valve lies to the wastegate under ECU (engine control unit) control. The boost control solenoid contains a needle valve that can open and close very fast. By varying the digital control frequency to the solenoid, the solenoid valve can be commanded to be open a certain percentage of the time. This affectively alters the flow rate of air pressure through the valve, changing the rate at which air bleeds out of the T in the manifoldpressure reference line to the wastegate. This effectively changes the air pressure as seen by the wastegate actuator diaphragm.

 

[97gsxturbo97]

well boost cut is disabled by dsmlink by default. Not sure why it wasnt knocking though.

 

[97gsxturbo97]

I was told that the t25 doesnt really push any more air at 22 psi than it does at 15 psi so its unlikely that any damage did occur. Is this true?

 

[97gsxturbo97]

Sorry about all the questions but I would rather not open up a new thread. Ive been reading and reading and found out that the wastegate should only allow around 8-10 psi. So why is my car running at 15 psi off the wastegate. Is the 3 inch downpipe and no cat causing this? Im trying to figure this out so I dont blow up my daily driver thinking its fine.

 

[knochgoon24]

Sorry about all the questions but I would rather not open up a new thread. Ive been reading and reading and found out that the wastegate should only allow around 8-10 psi. So why is my car running at 15 psi off the wastegate. Is the 3 inch downpipe and no cat causing this? Im trying to figure this out so I dont blow up my daily driver thinking its fine.

Basically, your exhaust flows so well that most of the exhaust can go through the turbo just as easily as it can go through the wastegate passage. If you run a nice 15psi I wouldn't worry about porting or anything.