Hi,

I'm having boost problems after 4500rpm, I lose all boost. Boost pattern is 0 - 4500 rpm - goes to 8 - 10 than after 4500 drains down. If I push over 4500 rpm a few times in a row, I hear a loud howling noise…

What I have done:

1. Replaced all vacuum lines
2. Replaced all one-way check valves
3. Tested all solenoids under Upper intake (including purge control, turbo control, etc…) – as per manual – all tested ok
4. Checked all 1” tubes – replaced one from air pump (Leaking)
5. Replaced ‘Y’ connector coupling – bad shape
6. Tested Charge relief and air bypass valve as per manual – seem to be ok
7. Removed all piping to turbos, both turbos spinning freely
8. Charge control valve seems to be working as indicated
9. Replaced the following gaskets:
a. ACV, Upper intake extension manifold, throttle body gasket and ‘O’ ring, turbo gaskets
10. Tested pressure and vacuum chambers for leaks – all ok

Where should I look next???

 

Pull the end off the CRV that runs it back into the intake and listen to hear if it closes after 4000 or so RPMs. If you are hearing a whoosh sound while still trying to accelerate after 4000+ rpms, the CRV is probably not closing (hence the Charge Relief solenoid may not be functioning correctly).

 

I have tested the Charge relief valve solenoid and it test ok?
I will try this when I return home this evenening...

 

If you get the whoosh and your sure the CRV solenoid is okay, then it is probably the valve itself that is bad.

 

The solenoids can respond differently to temperature or it could be working intermittently. If the CRV isn't closing, that will help you know where to start looking.

 

I have pulled the end off the CRV that runs it back into the intake and listened to hear if it closed after 4000 or so RPMs. It did...I could hear it close and feel it close as well...
Where to next???

 

So after 4000 rpms, the CRV closes but you are still losing boost (falls down to nothing after transition)?

Then it's got to be a vacuum misrouting or an inverted check valve.

 

Lack of air in the pressure tank (the black tank in front of the UIM) can cause failure to build secondary boost. Make sure the check valve feeding this tank is pointed in the right direction (blows towards the tank). Then hook a tee into this line with a pressure gauge and make sure pressure is being built up through 4500rpm.

-bill

 

Can't be vacuum line miss routing as I had the same problem prior to performing the vacuum line job.
I did replace all the check valves including the one going to the tank. I checked and it is pointing the right way.

The best way to describe the noise after 4500 rpm - siren type of noise...
Someone said that it sounds like my secondary is trying to spin backwards?
Make sense...

 

The siren noise could indicate that the ACV gasket slipped when you put the ACV back on after doing the hose job.

 

im actually having this exact same problem... at 4500, boost drops off to nothing, and if i go over 4500 through a couple gears, i hear this horrible noise that sounds like a siren... its driving me nuts cause i cant figure out what it is

 

The siren type noise was there before I did the hose vac job...

 

i have the same problem i heard that the rubber piping that goes from your air intake to your primary turbo can cause that my boost gauge get to about 7 then at 4500 rpm it just dumps all boost. supposedly that hose over time becomes really felixable and limits air flow to the primary turbo. so you might want to check that out if you figure out what it is post it because im sure were not the only ones who will ever face this problem

 

did you find a solution yet? or anyone else have any ideas?