Show full size 924Board.org
Discussion Forum of 924.org
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 Technical FAQ924 FAQ (Technical)   Technical924 Technical Section   Jump to 924.org924.org   Jump to PCA 924 Registry924 Registry

The Boost Has Gone Away
Goto page 1, 2  Next
 
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech.
View previous topic :: View next topic  
Author Message
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 1:26 am    Post subject: The Boost Has Gone Away Reply with quote

This is not the title of a new song I'm writing...unfortunately!

So yesterday morning, everything was normal.* Yesterday afternoon, my car seems to have spontaneously converted into a normally-aspirated car. Vacuum on the vac/boost gauge seems normal, and as I accelerate, the needle moves up to 0 and...stops there.

I don't hear anything from the turbo. On an RX-7 turbo from a previous life I blew off some connection at the intake and got no boost, but it was accompanied by a loud WOOOSH as the turbo blew air into the atmosphere. Could this be my wastegate stuck open? These wastegates are pretty big, do they flow enough to completely eliminate boost?

*Normal for me is not really normal...I have had a problem since I've owned the car where I overboost to about 1 bar if I let it, and it seems to build boost a bit slower than it should. My working theory was the wastegate was stuck partially open. Maybe it blew open all the way and stuck there?
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
CÚdric  



Joined: 27 Aug 2004
Posts: 1920
Location: Sweden

PostPosted: Thu Feb 14, 2019 1:59 am    Post subject: Reply with quote

Sounds exactly when my recirculation valve on the turbo got stuck due to a broken rubber seal. Pretty easy problem to fix.
_________________
┤80 924 Turbo
Back to top
View user's profile Send private message MSN Messenger
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 2:01 am    Post subject: Reply with quote

Can that be done in situ? I'm not actually sure what/where that is...

CÚdric wrote:
Sounds exactly when my recirculation valve on the turbo got stuck due to a broken rubber seal. Pretty easy problem to fix.

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
Carrera RSR  



Joined: 08 Jan 2010
Posts: 1880
Location: Somerset, UK

PostPosted: Thu Feb 14, 2019 2:05 am    Post subject: Reply with quote

Check for obvious boost leak first. A boost whoosh is not a given from a leak

Overboosting as you describe could be because the waste gate was not getting full boost signal due to a leak in the control line.
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
Back to top
View user's profile Send private message
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 3:20 am    Post subject: Reply with quote

Very good point. I'm going to kick myself if the overboost is a leaky control line...

Carrera RSR wrote:
Check for obvious boost leak first. A boost whoosh is not a given from a leak

Overboosting as you describe could be because the waste gate was not getting full boost signal due to a leak in the control line.

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
924RACR  



Joined: 29 Jul 2001
Posts: 8218
Location: Royal Oak, MI, USA

PostPosted: Thu Feb 14, 2019 6:20 am    Post subject: Reply with quote

I had this happen one day to my 931.

The spinny bit stopped spinning: coking of oil under the heat shield under the turbine wheel (inside the turbo unit itself) had pushed the heat shield into the backside of the turbine wheel until the turbo couldn't spin any more. No boost.
_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
Back to top
View user's profile Send private message Send e-mail Visit poster's website
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 6:24 am    Post subject: Reply with quote

Supposedly, this turbo was rebuilt or refreshed or something a few years before I got it (seller didn't have details) so I'm certainly hoping that's not the case. But...yeah, that would do it...

924RACR wrote:
I had this happen one day to my 931.

The spinny bit stopped spinning: coking of oil under the heat shield under the turbine wheel (inside the turbo unit itself) had pushed the heat shield into the backside of the turbine wheel until the turbo couldn't spin any more. No boost.

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
Mike9311  



Joined: 14 Dec 2004
Posts: 735
Location: Chicago-ish

PostPosted: Thu Feb 14, 2019 7:55 am    Post subject: Reply with quote

On a S2 check if you popped the intake to throttle body

A lot of people don't have the black seal/spacer between the intake tube and throttle body. If they also don't have the screw in the hold down bracket (or even if they do) it is possible to blow out the throttle body o-ring (orange). The or-ing will check stick out a little bit between that interface.

I had this happen and it feels as you described
_________________
1980 931 ...off with the cobwebs
1982 931 Entwicklungsfahrzeug
1979 924 NA M471/M481 ohne M650 Herausnehmbares Dach
1982 931 Red Resurrection - NEW!
1982 931 parts car or resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
Back to top
View user's profile Send private message
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 9:03 am    Post subject: Reply with quote

Interesting...I don't have the black seal, but I did once pinch the orange o-ring on reassembly, and the car would barely idle. I'm certainly not seeing that, as it seems to idle and run fine. I'll definitely check it out though...

Mike9311 wrote:
On a S2 check if you popped the intake to throttle body

A lot of people don't have the black seal/spacer between the intake tube and throttle body. If they also don't have the screw in the hold down bracket (or even if they do) it is possible to blow out the throttle body o-ring (orange). The or-ing will check stick out a little bit between that interface.

I had this happen and it feels as you described

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 9:05 am    Post subject: Reply with quote

Just out of curiosity, with a wide-open stuck wastegate, should a stock S2 turbo be able to flow enough to get positive boost?

And on the other end, with a wastegate stuck closed (or a disconnected boost control line) how much boost should it be able to make?
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
Fasteddie313  



Joined: 29 Sep 2013
Posts: 1839
Location: MI

PostPosted: Thu Feb 14, 2019 11:22 am    Post subject: Reply with quote

bureau13 wrote:
Just out of curiosity, with a wide-open stuck wastegate, should a stock S2 turbo be able to flow enough to get positive boost?


Maybe not.
Tiny turbo, huge wastegate. It might not make any boost at all with the WG stuck open..

bureau13 wrote:

And on the other end, with a wastegate stuck closed (or a disconnected boost control line) how much boost should it be able to make?

Million PSIs.. Way too much..


Take your WG line off of your upper charge tube, turn your air compressor regulator down to like 30psi, shoot air into the line on and off and it should cycle the WG open with pressure and closed after you take the pressure off..
It will sound like an old squeeky spring..
Send a few CCs of oil down the line and cycle it with your air compressor a bunch of times..


The recurculating BOV in the compressor housing, yes I think you can replace the gaskets on each end of it while it is in the car.. 10mm
Their are no gaskets inside it, just on each cap..


See those 4 10mm bolts around that cap? Their is one on each side..

You can even take the compressor housing off the turbo without removing the turbo if you are really good with a 10mm wrench in tight spaces

Can you hear your turbo spinning in your exhaust sound at all? Could you ever?

The first thing I would do is cycle the WG with an air compressor like I said and see what you get.. Cycle it a bunch of times to exercise it and maybe even shoot a little oil down there and keep cycling..

I wouldn't put too much pressure on it like 100psi because you might pop it, but if you can't get it to cycle at all you are going to have to take it off anyway..


You could take your downpipe off of the turbo and WG to finger the turbine and see the position of your WG but that's hard work..
_________________
80 Turbo - Slightly Modified
Back to top
View user's profile Send private message Yahoo Messenger
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 11:49 am    Post subject: Reply with quote

Very good idea...something I can try that doesn't require hours of work that may be pointless!

I do not hear any turbo sounds at all right now, and when it was working, I could hear it pretty clearly with the windows down.

Fasteddie313 wrote:
bureau13 wrote:
Just out of curiosity, with a wide-open stuck wastegate, should a stock S2 turbo be able to flow enough to get positive boost?


Maybe not.
Tiny turbo, huge wastegate. It might not make any boost at all with the WG stuck open..

bureau13 wrote:

And on the other end, with a wastegate stuck closed (or a disconnected boost control line) how much boost should it be able to make?

Million PSIs.. Way too much..


Take your WG line off of your upper charge tube, turn your air compressor regulator down to like 30psi, shoot air into the line on and off and it should cycle the WG open with pressure and closed after you take the pressure off..
It will sound like an old squeeky spring..
Send a few CCs of oil down the line and cycle it with your air compressor a bunch of times..


The recurculating BOV in the compressor housing, yes I think you can replace the gaskets on each end of it while it is in the car.. 10mm
Their are no gaskets inside it, just on each cap..


See those 4 10mm bolts around that cap? Their is one on each side..

You can even take the compressor housing off the turbo without removing the turbo if you are really good with a 10mm wrench in tight spaces

Can you hear your turbo spinning in your exhaust sound at all? Could you ever?

The first thing I would do is cycle the WG with an air compressor like I said and see what you get.. Cycle it a bunch of times to exercise it and maybe even shoot a little oil down there and keep cycling..

You could take your downpipe off of the turbo and WG to finger the turbine and see the position of your WG but that's hard work..

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
Fasteddie313  



Joined: 29 Sep 2013
Posts: 1839
Location: MI

PostPosted: Thu Feb 14, 2019 12:11 pm    Post subject: Reply with quote

If you have access to the top port of your WG you can also put some pressure on that side too to force it closed if it is really stuck wide open, effectively increasing your spring pressure..

https://www.youtube.com/watch?v=Anv-SrWNB5w

I turned a blood pressure tester thing into a device to add pressure to the top port of my WG, increasing the spring pressure, and I am very curious to see if it will be an effective method of boost control for me when I am ready to start turning it back up..
I have the gauge and handpump thing nicely mounted beside the radio in the car now.
I think adding air PSI to the top port will raise the boost it opens at like putting in a stiffer spring.
If it works I think it will be an awesome and unique way of controlling my boost just like putting in a heavier spring but finely adjustable..
Hopefully I can figure out how much gauge pressure gives me how much effective boost and I'll be able to set whatever boost level I want with a few squeezes easily and repeatably in fine increments so I can set it to 6psi, 10 psi, 12, 13, 18, 20 whenever I want and set it to exactly what I want by the gauge reading..

Crazy and off topic..
_________________
80 Turbo - Slightly Modified
Back to top
View user's profile Send private message Yahoo Messenger
bureau13  



Joined: 07 Sep 2017
Posts: 196
Location: South Florida

PostPosted: Thu Feb 14, 2019 12:26 pm    Post subject: Reply with quote

Some boost controllers work that way, essentially. I tried to access that area once, but I don't see how you can get at it from either top or bottom, without removing it from the car.

Fasteddie313 wrote:
If you have access to the top port of your WG you can also put some pressure on that side too to force it closed if it is really stuck wide open, effectively increasing your spring pressure..

https://www.youtube.com/watch?v=Anv-SrWNB5w

I turned a blood pressure tester thing into a device to add pressure to the top port of my WG, increasing the spring pressure, and I am very curious to see if it will be an effective method of boost control for me when I am ready to start turning it back up..
I have the gauge and handpump thing nicely mounted beside the radio in the car now.
I think adding air PSI to the top port will raise the boost it opens at like putting in a stiffer spring.
If it works I think it will be an awesome and unique way of controlling my boost just like putting in a heavier spring but finely adjustable..
Hopefully I can figure out how much gauge pressure gives me how much effective boost and I'll be able to set whatever boost level I want with a few squeezes easily and repeatably in fine increments so I can set it to 6psi, 10 psi, 12, 13, 18, 20 whenever I want and set it to exactly what I want by the gauge reading..

Crazy and off topic..

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
Back to top
View user's profile Send private message
924RACR  



Joined: 29 Jul 2001
Posts: 8218
Location: Royal Oak, MI, USA

PostPosted: Fri Feb 15, 2019 12:12 am    Post subject: Reply with quote

If you can get in there, see if you can turn the compressor wheel by hand...
_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech. All times are GMT + 11 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group