Can one of the experts confirm this before i start pulling things apart. (NOW FIXED)

[NixRX7]

Ok before i start pulling thigs apart can some one who knows there stuff give me there opinion.
I have an intermittent boost problem, most of the time the car runs well and boosts great thru all gears, good boost pattern etc.
Right the problem is that every so often when im am just cruising along at about half throttle when the revs reach 4500 the exhaust note changes, gets a lot louder/harsher now 4500rpm is when the second turbo kicks in, but the boost guage reads 0 and if i try to open the throttle more absolutley nothing happens it just carries on at the same speed with this real harsh exhaust note.
Now from reading another post somewhere i believe the problem may be caused by the turbo control solenoid in the rats nest which may have become to weak to operate correctly.
If i drop the clutch or let revs drop down below about 2500 then floor it everything is fine again and it pulls like a train.
It always happens when i am just cruising and the revs hit the 4500 point.

any help on this would be apprciated

[clive]

Is it definatly the exhaust note your hearing and not an underbonnet noise only dead Air pumps make some orrible noises ?

[NixRX7]

Its definatley a distinct change in exhaust note from the normal growl to a much harsher raw sound, and it stays like that even if i floor it, soon as i back off the revs it goes back to the normal exhaust note and i can get full boost agian

[jonrx7uk]

Have a good poke around under the UIM.  it sounds like a problem with either the Vacuum or Pressure side of the complicated Rats nest mess.  It may be a simple case of a split or kinked pipe.  i had a similar problem a while back where my hose to the vacuum chamber was kinked, stopping the 2nd turbo coming online.

Good Luck
Jon

[jonrx7uk]

If its the turbo control solenoid (as your other post), WGT sold me one a while back for about £20.00 by the way...

[NixRX7]

Just to confirm my suspicions, what happens on your cars when you are at partial throttle and you reach 4500rpm ?
I will have to go check but i am sure mines not making any boost at this point if i am only just giving it a bit of throttle.
If i go WOT all is fine, but at partial throttle it gets to 4500rpm and then i either get a wierd burp sound and then the change in exhaust note or it just goes straight to the wierd exhaust note.

[jonrx7uk]

You need at least 7psi for the 2nd turbo to come online, so at part throttle at 4500rpm there should be no 2nd turbo, if that makes sense.  Do you have a boost guage fitted?

[NixRX7]

Yep got a boost guage, and if i accelerate up throught the gears everything works as it should, its when i am just driving along in traffic etc, just giving it a bit of throttle and the revs reach 4500rpm the exhaust note changes completley, if i then floor it, absolutley nothing happens, i have to back right off then accelerate and all is well again, during all this the boost guage usually reads 0 or below.

I have the following mods: Straight thru exhaust, Power FC, HKS induction.
The PFC was mapped recently at WGT

[NixRX7]

Just had a thought, below 4500rpm the wastegate is not controlled by the ECU but above that it is (i think) i wonder if the PFC is opening the wastegate at 4500rpm regardless of boost pressure, its the only thing i can think of that would cause such a change in the exhaust note.

[jonrx7uk]

Check out http://rx7.voodoobox.net/index.html

Click on "how to" and "solenoid valve test"

He has had the same problems as you.

[jonrx7uk]

Having read that, it does sound like a bad turbo control solenoid.
Good luck changing it!  It can be done with the Rats nest in place, its just a bit difficult to get the plug off the back of the solenoid...

Cheers
Jon

[jonrx7uk]

Check out http://rx7.voodoobox.net/index.html

Click on "how to" and "solenoid valve test"

He has had the same problems as you.

Im getting confused, have you got 2 posts up about the same thing?

[NixRX7]

Right i think i have fixed it, pulled all the intake hoses off and found the little brown BOV type thing was very loose, took it right off and replaced the bit of hose and put on new clips to hold it on nice and tight.
This seems to have cured all my problems, car now idles smoothly, no back fires on over run and boost is working correctly, even from cold when the car was right lumpy has been cured.
Cant believe one loose hose would have caused all my headaches.

Sorry yes i did have two posts, first was about diagnosing problem, second was after i thought i knew what it was and wanted a second opinion.

Hopefully all cured now.