Can't reach full boost, Wastegate closed, Loud whistling sound

[kddrosos]

After several sleepless nights of lurking and theorizing, I come to the land of the boost gods. I'm running an old SBR G60 turbo (T04E compressor/Mitsubishi 7CM hot-side) with a few years of heavy miles. My problem is that I spool normally to about 14psi at 4500RPM then pressure stops building. As soon as boost hits 14psi I can hear an audible whistling sound that rises in pitch with RPM. My 02-mounted external wastegate is not opening to where I can hear it (open dump). I have boost leak tested the entire intake and can hold 25-30psi on a shop compressor. There are some small leaks around the TB but I figured if the shop compressor can build the pressure, then my turbo should be able to just fine. My bypass valve is not leaking at all. I ran some Seafoam while cold and there is no smoke in the bay at all. I even unhooked all of my MBC lines and left the WG unhooked (yes, I was very nervous) and I still have this problem. My next thought was a bad turbo. I can't see any heavy smoke under boost. Last night I removed the turbo and everything looks totally normal. I find no soot or evidence of an exhaust leak at all. I have no oil in my exhaust or intake side and there is no in/out shaft play at all, only very slight up/down play that I've had for the last 2 years. My question is why my turbo wont build boost? Is it possible for a compressor wheel to spin at a different rate than the turbine wheel? The nut on the wheels don't feel loose at all. Thanks for any advice!
Kevin

 

[crash89]

Last time I heard something like you are describing, was a boost leak. So, is this a new thing? Has the turbo always only spooled until 14psi? What boost are you currently "running"? Have you removed the wastegate and made sure that the valve compresses?

 

[2gmitsueclipse]

The whistling sound is pressure escaping. Your other symptom is not building boost after 14 psi. You have a boost leak. They can be tricky to find. Is your wastegate closing?

 

[kddrosos]

What boost are you currently "running"? Have you removed the wastegate and made sure that the valve compresses?

I have the MBC set to approx. 20psi. I was completely convinced it was a boost leak until I tested. Now the only thing I wasn't able to test was the compressor housing itself because I have a 2.5" tester. For some reason it's mission impossible to find a 2.5" to 3" size-up. From the lower IC piping to the motor supports 30psi with minor leaks around the TB with the shop compressor. They do need to be fixed before I tune again but I should at least be able to build target pressure and hear the WG open. Nothing on the compressor housing is cracked or missing, so I have no reason to believe it's leaking. This problem happened overnight and the whistling/whirring sound only began when the problem started. If I turn my MBC all the way down, I can hear the WG open at 14psi (the WG's spring weight). One thing I even tried was putting the WG vac line on the top port to push down while boosting, just to see if I could blow my motor via over-boost (not really) and there was no change.

 

[risknjtsi]

try using a different mbc had a mbc spring fail on me did the same thing

 

[kddrosos]

I went ahead and removed it from the system when I ran the line strait to the WG. I, too, have heard of these things pulling some shady stuff like that though. Thanks for the suggestion.

 

[risknjtsi]

how about you change the spring in the wastegate just to see if it would boost past 14 psi then you will know were you stand on if your turbo has anything to do with it

 

[kddrosos]

I could add a small spring in conjunction with the large blue one that's currently installed, but that's the thing.. If the WG was opening enough to limit that kind of pressure build, I'd hear it. Like I said, when the MBC is adjusted to it's lowest setting, I can hear the WG opening (very distinct sound) at it's spring pressure. In fact I can hear the whistling at the same time. If I set the MBC higher I can only hear the loud whistling sound when hitting that 14psi point. If the whistling sound was the WG leaking, then it would have to build more pressure as I hold to redline. Otherwise I wouldn't hear 2 different sounds when setting boost to its lowest point. What's killing me is that the car runs totally normal during regular driving and the turbo's wheels spin freely. My car builds boost totally normally until that 12-14psi mark where it just flat-out stops building pressure, like a wastegate is controlling it. 3edgy5me

 

[blaster1812]

What BOV are you running?

 

[kddrosos]

Greddy Type S.. With the vac line hooked up, there's no leaking. I even tried a buddy's known-good Type-RS with no change. Honestly if it wasn't such a pain in the butt I'd hook up his whole turbo assembly and troubleshoot that way. I want to blame this on a boost leak more than anything but I've seen the test, and everything checks out. If it is a blown turbo, then why would it spin freely with almost no shaft play? Is there any way a pre-turbo exhaust leak could appear only at higher boost levels and not leave residue? Could the compressor wheel rub the compressor housing even if there's no in/out shaft play? I will don the title of Wizard to anyone who helps figure this out!

EDIT: After reading though the thread, I realized I didn't answer a previous question. I have been running about 21psi for a couple years now. I just noticed this problem coming home from work the other day. Literally came out of the blue.. or green.. or whatever. I've had a wastegate spring collapse on me before where I couldn't even build 5psi but I could hear the distinct open dump sound.

 

[97_4g63t]

You done your BLT per turbo right? Intake couplings and air filter are all good? Only other thing I could think of would be a cracked housing.

 

[kddrosos]

I couldn't test the compressor itself, but I tested from the lower IC pipe directly off of it. I'll look for areas of fault in the compressor housing but I still don't understand how a cracked or small leak can regulate boost pressure so tightly.. The effect I'm getting with maxing out at 14psi is reminiscent of wastegate characteristics.. It doesn't budge.. I'm really appreciating the attention guys, and helping with figuring this out

Also, I don't know if it's relevant, but before I removed the turbo I noticed a subtle whistling sound coming from the air filter at idle.. If I touched the throttle it went away but I've never heard it before.

 

[risknjtsi]

when your car hits 14 psi besides the fact that the boost is only at 14 psi do you feel any other difference in the car as it goes through the rpms

 

[BurrowZ]

I have to wonder the seemingly obvious.. Is your compressor housing not sealing well enough? If possible you really should test from your turbo inlet.

 

[97_4g63t]

That's what I was getting at testing per turbo. Try to test there and that would tell you if your compressor housing leaked. Only other idea would be maybe your turbine is loose on the shaft and not spinning your compressor wheel correct. Idk man just throwing ideas out there.

 

[kddrosos]

...do you feel any other difference in the car as it goes through the rpms?

I can hold to redline within safe AFRs and no knocking thankfully, but it's smooth. No misfiring, bucking, or dropping in pressure.

Is your compressor housing not sealing well enough? If possible you really should test from your turbo inlet.

I'll try to get some couplers tomorrow. I'll have to test the turbo while off the car. If it holds pressure OK then I won't be alarmed, as this is to only be expected of my luck.

Only other idea would be maybe your turbine is loose on the shaft and not spinning your compressor wheel correct. Idk man just throwing ideas out there.

It's not far from reality at this point. Maybe at a certain pressure the compressor wheel becomes unable to remain fixed on the shaft. It could explain the whistling sound, but the sound also rises in pitch with RPM. That and I've never seen damage from a rogue spinning wheel on a turbo shaft but I can imagine the heat buildup being significant. I'll check the nut now. I have no idea if this turbo was balanced on a VSR though.

 

[risknjtsi]

hey just checking did you figure out your problem

 

[daplatano91]

Have you taken the downpipe of to insure theres no damage to the exhuast wheel causing you not to fully spool?