This little maze of pipe work is starting to fascinate me..

I took the WRX to work today because my other half had to drive to work herself and after this weekends "wheel bearing incident" she is a bit dubious about the car so she took mine instead.

Anyway..

I've never really driven it in traffic before so I've not had a chance to listen to all of the noises it makes when its hot and bothered.. I noticed an odd deep tapping noise for few seconds every time the revs dropped to idle speed, I thought to my self "oh my god what's wrong with this thing now".

Got to work and popped the bonnet and gave it a good rev and let it settle while listening closely to the block, NOTHING.. So I got back in the car and gave it a rev and there was the tapping as before?

So I gently teased the throttle under the bonnet and let the revs climb ever so slowly and surely enough "tap, tap, tap, tap, tap" from the drivers side strut, I held the solenoid just to be sure that's where it was coming from and it wasn't an injector..

So my question really is: What in gods name does this thing do when the turbo isn't boosting?

And on a particularly ****ty note: The whining noise IS still there, had my fingers crossed that it was the wheel bearing.

 

You have already found the other thread, which I think answers most of your questions. As someone touched on in the other thread, I think the boost solenoid switches on and off as the revs go up slightly, in an attempt to relieve lag?

Reference your whining noise, is it engine/gear box related? In other words does the whining match the engine revs or not, or is it worse in a particular gear? Does it continue when you dip the clutch and coast?

 

I thought you were the expert Davey?

Telling us all how things should be in one thread, and then pleading complete ignorance in the next isn't exactly expert behaviour.

The behaviour you describe is normal, and dependant on the boost control maps.

 

There's a slight difference when referring to basic engine components, this is a specialist part, I understand what its job is, I'm just asking why it behaves in this way when not on boost. If that's difficult to understand then I do apologise for being CLEARLY stupid.

The noise is with road speed and only under load. It starts above 40mph and only when your on the throttle, even very lightly. My money is on a layshaft bearing.

 

Or the input shaft maybe, definately sounds like it's gearbox related. I take it you have checked the gearbox oil level. Might be worth renewing the gear oil, maybe even for a slightly thicker grade.

 

I've not removed the gearbox to inspect it but it has sufficient oil, infact the oil was WELL over the fill level, I believe the previous owner filled it through the dip stick tube and over-filled it.. The oil looks good to, no visible particles or discolouration..

 

Boost control purge solonoid...read it up (also known as a wastegate control solonoid)

Pretty much any Turbo car with ECU controlled boost pressure has one. And it works on the principal of pulse width modulation


It will also provide the answer as to why you only need a 5psi wastegate as standard to run 14psi

 

Can you elaborate Ali?

Rob.

 

Still dont understand the purpose of pulsing at low revs? Whats the physics behind that to help with spool up?

 

It pulses as it works on pulse width modulation to control amount pressure purged from the wastegate. It can only work as on or off, so needs to constantly switch at varying rates to achive the desired target pressure.

Due to having a 5-6psi wastegate it will start to open very prematurely without it, so pressure needs to be continually purged above idle speed.

 

To relieve back pressure prior to boost development???

 

Sorry, I should have waited a min!

 

Am I correct in saying when the solenoid pulses the wastegate is opened and closed?

 

no, it only modifies the pressure the wastegate "sees"

 

No it keeps it shut.

 

Ahhh now I understand