Boost Issues. Very erratic control.

[David15151]

Ok basically, the problem is that there is something going on with the boost control. I have my MBC backed out all the way. Now, the boost should only be able to go to about 9psi and thats it. It does that.. SOMETIMES.. other times i get no control at all and the boost just keeps climbing. I can sometimes take it all the way to redline and it stays at 9psi other times ill hit 4k rpm and its climbing way above 15psi and i have to let off. Now.. the possible problems in my head right now are... Broken boost controler? sounds far fetched to me. Wastegate is going out? Dunno if those are signs or how to test it. Or the door itself is getting caught or stuck.. I did mess with the door to see if it gets stuck at all and it seems to open and close without a problem. So my guess would have to be the wastegate it self.... Where would i start as far as finding the problem.

 

[ddavisaf]

Wastegate itself could definately be the problem. You also could have a torn vacuum line going to the wastegate.
You are however using a 16G with aftermarket exhaust. So you could be creeping.

 

[David15151]

na its not creep, i had creep before.. replaced the turbine housing. It will hold at 9psi all the way to redline sometimes so it cant be creep. I just cant figure out why sometimes it holds and sometimes it doesnt.

 

[ddavisaf]

I didn't pay attention to what I read. Creep isn't it for sure.
So it's either your wastegate isn't triggering your flapper open due to a torn or damaged vacuum source. It's possible that you're wastegate is bent inward some causing it to not be able to open all the way.
2nd gear has more of a load than 1st, 3rd more than 2nd. So your boost is harder to control than the previous gear. So lets say you're not having a problem in first, but you do in second.
First thing I would do would be to take the wastegate off, and reinstall it with some washers. Try one or two to start with. Make sure that it is still sealing off your flapper port entirely. Post back and let us know how that goes.
Also if it doesn't help post back what you're reading for vacuum at idle please.

 

[David15151]

well i can tell you i was only doing 3rd gear pulls to test it. i would do a pull.. get no control.. let off.. then do another pull and it pulls all the way to 6k totally controlled. So its just on or off. Vac at idle is about -15psi

 

[ddavisaf]

Your vacuum reading is slightly low. Normal vacuum is 19-21. However it still changes depending on where you're located.
I would definately inspect for a damaged vacuum line first since it's easier. Everything related to the turbo. Then try the washer trick for the wastegate. If neither works then we'll go from there, but try both of these first since they're extremely cheap and easy.

 

[tselling]

after you check your vac lines i would do a pressure test on the actuator and see if it opens at 11.2 psi and do ir 3 or 4 times to see if that is sticking and not opening your wastegate. if so just replace the actuator for 10 bux or so (used) or 55 (new)

 

[oldman]

David15151 : Disconnect the mbc and run the pressure source directly to the actuator. If problem fixed, it's the mbc. If problem persists, perform a boost leak test like already suggested.

I can sometimes take it all the way to redline and it stays at 9psi other times ill hit 4k rpm and its climbing way above 15psi and i have to let off.

Because of this statement, I'm not willing to rule out boost creep. Does it hit 9psi first then climb slowly as rpm increases? Boost creep can sometimes get covered up by boost leaks, perhaps you have a intermitten boost leak some where.

 

[David15151]

it either holds at 9psi or doesnt pause at all in climbing.

 

[oldman]

it either holds at 9psi or doesnt pause at all in climbing.

Then it's not boost creep, have you try bypassing the mbc yet? Due to the inconsistency of the problem, a defective mbc not sending consistent signal to the actuator is very probable.

 

[David15151]

im going to try to bypass that MBC tomorrow and see what happens. thanks for the help so far guys.

 

[David15151]

ok, ran the car with the boost source going right to the wastegate today, sucker held at 9psi all day long... boost controller was the problem, it must be messed up. So glad it was just that. The ole Joe P MBC has failed me. hehe oh well time to shop for a new controller . THanks for the help guys!

 

[oldman]

Good deal. Before you buy a new one, take apart the old one and make sure that the spring did not wedge itself side ways. Also, I think 9psi is a little low as most are reporting 10-12 when running without mbc/bcs, a boost leak test might be a good idea anyway.

 

[David15151]

ok ill work on that next then.

 

[David15151]

Ok i once again need help with this issue. I got a new MBC today and hooked it up.. SAME problem. It wont control the boost unless i pretty much take the screw out. It WILL control boost if i bypass the MBC, but soon as i hook it up bam.. way out of control. I am so confused. I checked i had it hooked up right about 3 times and even called the company to make sure. Anyone have any ideas.. or did i just get a bad MBC .. sigh.

 

[David15151]

bah! nevermind.. looks like the spring fell out of the boost controller.. how i was lucky enough to find it in the dark wedged next to an intercooler pipe after i took my car for a drive is beyond me... but i got it back in there.. it works.. just spikes 1-2psi which is bleh.. but at least it controls the boost.

 

[oldman]

just spikes 1-2psi which is bleh.. but at least it controls the boost.

Try this.

 

[David15151]

jeez oldman , you are like a library of dsm info.

 

[oldman]

jeez oldman , you are like a library of dsm info.

No need to remind me I'm a postwhore.