I am running stock boost on 99 twins. When my car is running perfect it will boost 10-8-10 like it should. Occasionally when the switch for the secondary turbo is reached, it will only boost to 5 psi on the secondary. It will do that every few days, and will last most of the day. Sometime it won't do it at all. I suspect something might be sticking on the turbo, but I cant seem to find an issue. If someone could lead me in the right direction that would be much appreciated. All vacuum lines have been replaced. This problem only started about a month ago.

Thanks,

 

one of the boost control solenoids might be staying open . its the double solenoids that you can actually see on the upper intake manifold

 

Ok thanks, what is the best method for cleaning the silonoid. Is this usually a common issue?

 

yes its normally common. problem is the cars are old and the solenoids sit and bake on top of the motor for all these years. i have a couple working sets if you're interested

 

also take a look at the flapper that controls the secondary turbo make sure it moves back and forth freely. you can reach it from under the car it has a long rod just push it back and forth make sure there isnt too much resistance... might be time to replace some of the vacuum lines while you are at it.

 

Ok I will check the flapper valve tonight. All the vacuum lines were replace about the months ago, but the problem was there before. If there is about of resistance in the rod, is it best to take it apart and clean it? As for the silonoid is there any way to test them, or is it just easier to replace them?

Thanks guys

 

uhhh... Ok..... there are 2 vacume lines comming from teh turbo actuators ... did you replace those to??? they are thicker then the regular vacume lines .


I and J are the lines you are interested in , they go form the turbo / wastegate solenoid , to the actuators .

 

Marked

 

I had a similar problem a lond time ago when I had twins. For me it turned out the y-pipe outlet coupling was a little lose. Tightened down and never had a problem since.

 

Having the same problem at the minute. Running standard sequential, replaced two solenoids yesterday that were sticking in the black box. Took her for a run and no change still not gettin away after 4500. Then have the moo sound. All vacuum lines replaced as well. Checked the two solenoids at the top today, seem to be ok as well. I'll have a look at the flapper tomorrow

 

This was my problem back in the day with my stock twins. Cracked plastic Y pipe. The crack was hairline and it would open and I wouldn't get enough boost to transition to the second turbo.

I didn't realize the problem until I swapped them out for a single turbo. But there is a reason they redesigned the Ypipe. It is a common failure point.

It's almost certainly a boost leak. You always see the boost drop to 5 or 6 psi like that at transition when you have a boost leak.

You can check the actuator rod as mentioned but I bet its a boost leak and like T-Von mentioned it could the problematic Y pipe.

 

Found a problem here this morn guys, clip holding the actuator rod to the flapper has parted company. Hopefully thats it, I'll have to get one and try it, but Ireckon thats it.