Turbo / wastegate issue

Dan89_930 · 05-30-2008, 01:44 PM

Good afternoon. My "new" purchase (I know, I know, I have to post pictures - I will shortly) - a bone-stock '89 930 cab - sat in the seller's garage for the majority of the past 11 years. My mechanic spent the last 6 weeks replacing virtually all belts, hoses, gaskets and seals (no, he did not crack open the engine case), replaced all the shocks, and installed a center-spring clutch disk. The turbo and wastegate were deemed to be in great shape.

I'm leak free now and VERY happy.

Anyway, here's what's going on - I live about 10 minutes from the freeway. By the time I get to the freeway the car is sufficiently warmed up so I'll put my foot down on the freeway on ramp wanting the turbo to spool in second, third, and fourth gears. Well, there is no spool. Weirdly (if that's a word), after I drive for about 15-20 minutes trying to spool the turbo, it finally spools and the rest of the drive is a blast - perfectly normal spooling.

This has been the pattern for the half dozen times I have taken the car out since getting back last week.

Have any of you had similar experiences? Is it simply re-checking the turbo and the wastegate (and being prepared to replace as needed)? I think it is nothing more than this, but I was wanting to tap into this board's wealth of knowledge, experience, and suggestions.

Any thoughts you have are welcomed. Thanks.

Dan

Current ride
'89 930 Cab - Bone stock, 21K miles, VIN # 584 out of a production run of 600

Former rides
'97 993tt
'89 930 3.4l (Ruf BTR kit, US installed)
'86 Carrera N/A

'05 WRX Sti (thinking it would replace the three "Former rides" - boy, was I wrong!!)

JayG · 05-30-2008, 01:56 PM

Sounds like the wastegate is stuck open and no boost can build. Doesnt really explain why it starts working later unless it "un-sticks". Thats the only thing I can think of that would fix it self.

les_garten · 05-30-2008, 03:45 PM

Hi,
I guess when you say spool, you mean that you are making no power and the boost gauge is showing no boost? Additionally, the car should feel terribly underpowered after 4000 RPM. There are aluminum and Stainless components to the wastegate, and they are dangling in a relative breeze, so it may take them longer to warm up, and the Aluminum and SS will expand at a different rate. Usually Wastegates will stick shut and not stick open. If it was working fine when you parked it, how would it mysteriously open itself and stick open, which would be under spring pressure. I don't know, just seems strange.

infraredcalvin · infraredcalvin's Garage

Could it be an exhaust leak? Once the pipes get really warmed up they seal?

Dan89_930 · 06-05-2008, 08:07 PM

As promised, here are photos of my newest ride.

We still haven't figured out the no-boost-until-the-engine-is-quite-warm issue. We're pretty sure it's not the wastegate or the turbo, but we're still testing things out. I'll let you know what we find when we find it.

Dan

Dan89_930 · 06-10-2008, 02:19 PM

Quick recap of the problem - the car sat in the seller's garage for the last 5 years - probably closer to 7 years. When 930's sit without being driven, belts, hoses, gaskets, seals, etc. can fail. At best, most will not function properly.

Until the motor was running nice and warm, I could not get charged air (boost) into the motor. Once the car was warm, boost was mostly normal.

The problem (no boost until the engine got really warm) wasn't the wastegate or the turbo. There is an aluminum alloy tube / pipe / housing that connects the turbo to the intercooler - it called the "valve housing". Inside the valve housing is a piston that slides up and down the housing - its purpose, as I understand it, is to regulate the amount of charged air into the intercooler before, during, and after the engine warms up. The warmer the engine, the more charged air is allowed into the intercooler (not sure this explanation made complete sense, but that's how my mechanic explained things).

At both ends of the housing are "O" rings / gaskets. Because the car had sat for so long, these "O" rings became brittle and cracked and failed. The mechanic took apart the valve housing, found lots of little pieces of those "O" rings and determined the little bits and pieces were causing the piston to not function properly. The mechanic clean up the housing, replaced the "O" rings, reassembled everything and the car now runs perfectly.

I had never heard of this before. I thought it was just a straight shot from the turbo to the intercooler. Interesting, eh?

Dan

les_garten · 06-10-2008, 05:27 PM

Quote:

Originally Posted by Dan89_930

Quick recap of the problem - the car sat in the seller's garage for the last 5 years - probably closer to 7 years. When 930's sit without being driven, belts, hoses, gaskets, seals, etc. can fail. At best, most will not function properly.

Until the motor was running nice and warm, I could not get charged air (boost) into the motor. Once the car was warm, boost was mostly normal.

The problem (no boost until the engine got really warm) wasn't the wastegate or the turbo. There is an aluminum alloy tube / pipe / housing that connects the turbo to the intercooler - it called the "valve housing". Inside the valve housing is a piston that slides up and down the housing - its purpose, as I understand it, is to regulate the amount of charged air into the intercooler before, during, and after the engine warms up. The warmer the engine, the more charged air is allowed into the intercooler (not sure this explanation made complete sense, but that's how my mechanic explained things).

At both ends of the housing are "O" rings / gaskets. Because the car had sat for so long, these "O" rings became brittle and cracked and failed. The mechanic took apart the valve housing, found lots of little pieces of those "O" rings and determined the little bits and pieces were causing the piston to not function properly. The mechanic clean up the housing, replaced the "O" rings, reassembled everything and the car now runs perfectly.

I had never heard of this before. I thought it was just a straight shot from the turbo to the intercooler. Interesting, eh?

Dan

Hi,
That is the Shuttle valve, recirculating valve or blow off valve, whichever you want to call it. Makes sense now. Good one!

930turbo · 930turbo's Garage

The shuttle valve - or recirculating valve - has nothing the do with regulating air flow through the intercooler. It also should remain fully closed when at rest like the wastegate. Manifold vacuum pulls the valve open, it could be hanging up in the bore when the valve body is cool - if this is in fact the culpret. Be careful if it is hanging open as this will allow the turbo to free-spool and could overspeed to the point of distruction.

les_garten · 06-11-2008, 10:14 AM

Dan_930,
I think it would be instructive for you to get a better understanding from your mechanic on what the Shuttle valve, Bypass valve, recirculating valve, or blow-off valve does. It is called all these things by various wrenches. It's purpose is not exactly as you stated.

I no longer have one like yours but they all do similar duties. When you take your foot off the throttle when in boost, this valve receives a pressure signal from below the throttle blade that goes from + Manifold pressure to a rapid change to a relatively negative manifold pressure (ie vacuum). This causes the recirculating valve to open and allow the turbo to spin against little resistance by recirculating the intake charge from the Intercooler around in a circle within the intake circuit. If this were not in place the Turbo would spin against the closed throttle blade and encounter very high manifold pressure. This would cause the Turbo to spin down rapidly and possibly shear the Turbo shaft in half. You should ask your wrench to trace the path for you while you are standing next to the car. It makes a lot more sense that way. Typically those O-rings fail and you make boost but not as much boost, or you hear a clicking sound when you snap the throttle open and closed.

beepbeep · 06-11-2008, 01:25 PM

Yeah, what others said. The cylinder thing is nothing more but old-style BOV. Most of the time, O-ring will just crumble and piston will make clapping noise.

But yours jammed the piston open so it was "recirculating" all the time. You are lucky if your turbo survived as this is abnormal case and it will easily overspeed at full throttle if BOV is jamed open.

beepbeep · 06-11-2008, 01:25 PM

Yeah, what others said. The cylinder thing is nothing more but old-style BOV. Most of the time, O-ring will just crumble and piston will make clapping noise.

But yours jammed the piston open so it was "recirculating" all the time. You are lucky if your turbo survived as this is abnormal case and it will easily overspeed at full throttle if BOV is jamed open.