Car wont boost over 4psi?

[Shiesty2000]

I dont's understang whats going on. I have a greddy sp2 exhaust and a cold air intake but I had to take it off for waranty shitt so now my car is bone stock and for some reason the boost only went up to 4psi so I just put a joe p mbc in it and the same thing 4psi. Whats this all about?

 

[genius]

How is it that these problems always occur in threes!!! HAHA! If I stay on these forums too much longer I will start to have bad luck.

OK, if you completely disconnect and plug the sensor vac hose running to the wastegate actuator and the car attempts to over boost then you have a broken actuator.

If the car still won't boost past 4 psi then you have major issues with the wastegate itself.

And ofcourse, always check for cracks in the header, and you pipes. Any type of boost leak will cause you to have the same symptoms. Also check your T's! If you are using stock T's, they probably have cracks in them. These cracks won't be seen when you are in vac, they only appear when you are boosting. I can't stress it enough to check your hoses and pipe couplings!

 

[Shiesty2000]

How can I check for any leaks?

 

[genius]

How can I check for any leaks?

That's kind of tricky. I have heard of people using smoke machines or air compressors while plugging the intake track...

Just inspect all your clamps and silicones and check your T's be removing them and possibly just replace them since they are cheap. And make sure to use zip ties on all your T's as well.

 

[FlyinMSP]

If there's a leak in the vac lines under boost, wouldn't the boost go up??

 

[peepsalot]

If there's a leak in the vac lines under boost, wouldn't the boost go up??

depends if the vacuum lines are going to the wastegate or not.

 

[genius]

depends if the vacuum lines are going to the wastegate or not.

Exactly. If the leak is localized away from the wastegate, the whole system won't just depressurize because of it and to be honest, he probably doesn't have a leak in the vac hoses. If I was betting, I would think that if he has a leak at all it is in his actual pipe couplings.

He very well may have a bad actuator. I am interested to see what would happen if he disconnected the actuator altogether.

 

[Shiesty2000]

What is weird is about a week ago it was around 40 degrees and I was driving on the highway doing about 80mph in 5th gear and then punched it and it went up to 6psi with no boost contoller. At any other speed it wouldnt do it, it would only go up to 4psi.

 

[peepsalot]

Sounds like boost spike, if you cruise at a high rpm, and suddenly punch the accelerator, it happens. Did it eventually settle back at 4 if you held the accelerator? I would say it is unrelated to your low boost problem.

 

[Shiesty2000]

Sounds like boost spike, if you cruise at a high rpm, and suddenly punch the accelerator, it happens. Did it eventually settle back at 4 if you held the accelerator? I would say it is unrelated to your low boost problem.

It stayed at 6psi the whole time until I droped my speed below 80. And I also build no boost in 1st gear and I start to build about 2psi in second around 5000rpm's.

 

[Shiesty2000]

Exactly. If the leak is localized away from the wastegate, the whole system won't just depressurize because of it and to be honest, he probably doesn't have a leak in the vac hoses. If I was betting, I would think that if he has a leak at all it is in his actual pipe couplings.

He very well may have a bad actuator. I am interested to see what would happen if he disconnected the actuator altogether.

How do I disconnect the actuator?

 

[krillin]

check the gauge, check the all clamps. also check the plastic nipples where the hoses connect. there would be a hole since it's only held on by glue. also check the stock bpv. it could be leaking under boost.

 

[yashooa]

Hmm my actuator is passa-non-grata but I can still boost to 11-12 PSI it just spools like s*** and only hits boost way up high. Yours sounds way worse than mine but looks like I'll be doing MPI Nicks upgrade sooner rather than later.
Mine seems as if the wastegate is stuck partially open.
It does not seeem to move at all.

 

[jeffmsp]

where is your boost gauge hooked up? Is it alone on the vac line? If it is sharing a vac line it will read incorrectly. There may also be a small creak or leak on the hose/tri-fitting if you used the plastic hose that comes with many boost gauges like my autometer. Does the car feel like it is only boosting 4psi or just reading 4psi? also, 5th gear seems to always offer more boost spike, im pretty sure there is a relation between engine load and boost spike. btw dont boost 5th

 

[Shiesty2000]

where is your boost gauge hooked up? Is it alone on the vac line? If it is sharing a vac line it will read incorrectly. There may also be a small creak or leak on the hose/tri-fitting if you used the plastic hose that comes with many boost gauges like my autometer. Does the car feel like it is only boosting 4psi or just reading 4psi? also, 5th gear seems to always offer more boost spike, im pretty sure there is a relation between engine load and boost spike. btw dont boost 5th

The boost guage is T'd off of a vacuum line coming off of the intake manifold neer the fire wall, I think it goes to the fuel pressure regulator but I could be wrong. Another thing is, is that I thought it could be the boost guage so I keep messing with the mbc to try to raise the boost until I get fuel cut and nothing happens, I mean its hard to tell if im near 10psi if it is the guage.