Reading positive boost at idle. Help

[Simpfe]

Just fully rebuilt my 98 eclipse gst and took it out for a test drive to break it in and its way too fast seems like its running way over 20psi so I decided to install an AEM boost gauge and when I first start the car it reads -2 vacuum at idle and then when I shut the car off and turn it back on it will read +2, +3 boost at idle. The car also idles at about 750 rpm and the timing is spot on. The guy who owned the car before me blew the engine and the #2 cylinder leaned out and the piston completely came apart so I was assuming he was running way to much boost. I get up to about 4.5k rpm and the boost gauge hits 20psi so I'm sure the car is running well over 30psi. There is no boost controller on the car or even a MBC so I dont know why its running so much boost on the stock T-25. Or is there something wrong with the gauge? The turbo is in great shape also. The car only has 90,000miles and has a Greddy BOV, full greddy exhaust, and an Injen intake. Stock internals bored 20 over. And also I didnt hook up the Brown wire(Analog output-) and White wire(Analog Output+) that is coming off the AEM analog boost gauge. Only the 12v power(red), Switched 12v power(pink) and the Instrument lights(Grey) I tapped the Vacuum hose into the hose that runs from the intake mani to the solenoid that controls the fuel pressure regulator. When I was reading online on how to install this gauge, nothing said how to hook up that brown and white wire or if you need to.

 

[snowborder714]

Where is the AEM sensor getting its source of vacuum/boost from?

 

[Simpfe]

I tapped the Vacuum hose into the hose that runs from the intake mani to the solenoid that controls the fuel pressure regulator. Sorry just added that into my paragraph.

 

[spyderdrifter]

How does the car feel performance wise? A stock T25 like you said wouldn't give that much boost. Even my T28 won't give that safely. I too thought about where you may have tapped in the boost gauge.


Hook the boost gauge up on the line going from the fuel pressure regulator to its solenoid.

 

[Simpfe]

The car pulls very hard. This is my first time driving a turbo eclipse so I'm not 100% sure on how fast they are supposed to be on this stock turbo but it will roast the tires on a third gear pull. And I believe I'm tapped into the right spot for vacuum. Again I'm assuming its the stock T-25. Its Garrett and it looks like the stock size, very fast exhaust housing on it also which I believe is stock because our cars catch boost at low rpms correct? 2k - 2.5k rpm? Hardly any boost lag.

 

[spyderdrifter]

My T28 started building pressure around 2800, last eclipse had a T25 and did the same. I can chirp tires while up shifting from 1-2. I think the tires roasting are more on how its being driven and not necessarily the engine power, being that it's lightly modded.

 

[Simpfe]

I'm stumped on why I'm getting positive boost readings at idle and when I start to rev the engine the needle goes up a bit. And also with no boost controller installed what so ever wouldnt that make the wastegate function back to stock? Producing stock boost again? Would the size of the vacuum hose have an effect on the gauge reading? The hole being too small?

 

[spyderdrifter]

Too small of a hose maybe. But usually that has no impact. That would produce stock boost. I don't have a controller on mine, but I don't have gauge issues either. I know the factory boost gauge is quite irrelevant on our cars, but have you paid any attention to how it has been functioning since the AEM one is acting weird?

 

[Simpfe]

Well I can make a lot of cars chirp the tires while shifting gears but WOT at 4k rpms in 3 gear should not roast the tires unless your running serious hp without the handling to put that power to the ground.

The stock boost gauge is kinda all over the place, it will go way up to the + while driving around and at idle it will go up and down a bit. Totally off from the AEM gauge.

 

[2slow4now]

Maybe the wastegate is stuck closed. I would start looking at the wastegate and vac lines that operate it.

 

[curt-s]

If it's reading positive at idle and it's hooked up to a proper pressure source off the intake manifold, then the gauge or the sensor is faulty. Verify with another boost gauge or test this one against a known pressure source (ie. quality regulator on an air compressor)

 

[Simpfe]

I found out what the problem was. This AEM Boost gauge needs to be hooked up to a special Switched 12v where when you turn the key on/run it has power and then when you go to turn the key to start the car, it doesnt lose power and allows the gauge to calibrate. I had it hooked up to the ignition but when I would start the car it would lose power for a split second. I used #25 on the ECU Pinout and it works good now with -20 vacuum at idle, but the car is still running over 20lbs of boost. So that shall be fixed next! Thanks for the input guys!

 

[Dsmkauai]

Ya bro stop doing pulls at 20psi on that poor T25 or you will blow it fast!! Sounds like the wastgate is stuck if you ask me! And be carful roasting the tires and wheel hoping it can kill your trans fast if your not carful!