Wierd Boosting issue

[Epixinc]

okay wierd thing. i built my car from the block up with all stock parts, and sometimes when i go driving, i boost all the way to 15psi on my aftermarket boost gauge, other times it will only get to 9 or 10 psi on the gauge. .... what could cause this? the vacuum setup is as follows: it is running from the IC piping off the turbo to the Stock Boost Control Solenoid, then back down to the Wastegate. that is it. so what could cause it to sometimes give me max boost and sometimes not?

 

[RallyEclipse98]

Are you going up in gears as the boost decreases?

 

[Epixinc]

no its not like that... its either i get 10psi when i boost or i get 15psi. its kinda odd. one day i will get full boost through all gears, other days i will only get 10....

 

[Epixinc]

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[matt98eclipse]

I have the same issue your haveing. sometimes i will boost 16 psi and other times only boost 10. I would also like to know what this is!

 

[Epixinc]

wierd ass turbo cars!!!

 

[mndsm1]

Im not sure about dsm's, but I remember when I owned my SRT-4 when the weather was colder it would sho w more boost on the gauge.

 

[Mr Peepers]

Sounds like it's hooked up incorrectly, although it tends to change with the weather and other factors, especially with the stock BCS.

It should be hooked up as follows:

 

[Epixinc]

no no no! okay the pipe running from the turbo to the stock intercooler has a nipple on it. i run from that nipple(pressure source) to the MBC solenoid then to the waste gate. the stock setup has a t in place that runs to the back of the stock airbox which u can see on my photo just behind the K&N filter has a screw in it.

 

[Epixinc]

the yellow i circled is the nipples one on the intake which is capped, one on the pipe running to the intercooler and i put an arrow to the one on the wastegate. the pink is the vac lines i got running.

 

[Mr Peepers]

If you have the nipple just behind the MAS capped off, the BCS is not routed correctly; the air it bleeds off should go back behind the MAS, otherwise it is leaking metered air.

The BCS doesn't go directly between the pressure source and WGA- this is what you seem to be describing.

The stock BCS is NOT hooked up like a ball and spring MBC; it is a bleeder(ish) type setup.

 

[Epixinc]

well why does it work sometimes and not othertimes? so i need a vacuum source on the recieve side of the MBCS? and then the t has to be between the WGA and the IC piping?

 

[Mr Peepers]

Re-read my post above yours, it has been edited.

Rundown of how the BCS operates:
The default position of the solenoid is closed. When the car is ON the solenoid is opened and air can freely pass between the pressure source and nipple on the intake pipe. When you start to hit boost it stays open, bleeding off pressure before it can act upon the WGA. Once stock boost is achieved, the BCS will close; allowing the WGA to be pressurized and open the WG. It will continue to open/close/open/close to maintain a steady boost pressure.

If you have it directly between the pressure source and WGA, it will allow pressure to reach the WGA until a certain point/psi, then the BCS will close. The WGA will not close, but rather stay at that same position since air cannot leak from it(unless the BCS opens once again, controlled by the ECU). Where the boost goes after that point will depend on load, turbo characterisitcs, engine characteristics, weather, how much the flapper tends to blow open, how the ECU decides to control the BCS at that point, and many probably many other factors.

It's no longer a feedback system.

 

[matt98eclipse]

Matt, could a bad boost controller cause this problem to? Cause i have mine hooked pressure source to boost controller-boost controller to wastegate?

 

[architechnik]

If you're having trouble with your setup, Matt, it could be that the MBC ball is getting stuck. Then it won't bleed off when it is supposed to and the actuator will open (no more boost).

Because the MBC is a mechanical device it will get changes in accordance with temperature as well. A hot spring will cause more pressure but be more responsive, while a cold spring will not apply as much initial pressure but is less responsive. Try to keep the MBC away from the exhaust manifold and other hot parts to get more constant response.

 

[Mr Peepers]

Matt, are you using the boost control solenoid(BCS), the stock solenoid with the electrical plug connected to it, or a MBC? I assumed you were using the BCS.

 

[matt98eclipse]

Im not using the bcs. Im running just mbc.

Im using a cheap ebay pos! A nice one is on the list to get.

 

[Mr Peepers]

Ha, I got all sorts of confused. I thought you, Matt98eclipse, were the OP.

Too many Matts.

 

[Epixinc]

no i am the OP i am using the Stock MBCS