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 Previous  1, 2
 
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: 304
Location: South Florida

PostPosted: Fri Feb 15, 2019 12:30 am    Post subject: Reply with quote

What's the best way to access that with the turbo on the car? Remove the compressor-side intake tubing?

924RACR wrote:
If you can get in there, see if you can turn the compressor wheel by hand...

_________________
-----------------------------------------
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: 1994
Location: Sweden

PostPosted: Fri Feb 15, 2019 4:01 am    Post subject: Reply with quote

The recirk valve is quit easy to pull out if its housing with the4 screws. It was crushed gasket everywhere when removed the lid.
_________________
┤80 924 Turbo
Back to top
View user's profile Send private message MSN Messenger
924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Fri Feb 15, 2019 10:40 pm    Post subject: Reply with quote

bureau13 wrote:
What's the best way to access that with the turbo on the car? Remove the compressor-side intake tubing?

924RACR wrote:
If you can get in there, see if you can turn the compressor wheel by hand...


Probably...
_________________
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: 304
Location: South Florida

PostPosted: Sun Feb 17, 2019 6:52 am    Post subject: Reply with quote

OK, working on the least intrusive (and admittedly least effort) tests first.

I disconnected the wastegate control line from the top, and tried to pressurize it to see if it would hold. It does not. At all. It's wide open, not a "leak" but my hand vac pump couldn't pressurize it at all. I used an air compressor too, no dice.

What does that tell me? Well, unfortunately I don't know where the leak is. If it's a leak in the hose itself, then that would explain the overboost (although this big a leak would never have allowed the wastegate to open at all, so I think I would not have stopped at 1 bar). Of course, it could have become drastically worse, but it doesn't explain my current zero boost situation. Yes, that could be a different problem, if the overboost and zero boost issues are unrelated.

It could also tend to support my preferred (because it doesn't involve me needing a new turbo) theory, that the wastegate is completely stuck open...I think? In that situation, pressurized air goes where after it forces open the wastegate...out the top port/vent? That's my assumption. This theory involves the wastegate previously being stuck partially open, resulting in slow build of boost followed by overboost to 1 bar, presumably limited by the fact the wastegate was partially open. And now it's broken open entirely.

Sucks that the wastegate is such a pain to get to (no lift here). Might still make sense to remove that cover on the recirc valve on the turbo, just to see what's there. However, I'm wary of causing additional issues, and that wouldn't explain the issue with the wastegate/control line. So maybe since I know there's something wrong there, I just need to take that out and inspect it (and fix it) before moving to the next item...
_________________
-----------------------------------------
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: 2034
Location: MI

PostPosted: Sun Feb 17, 2019 7:42 am    Post subject: Reply with quote

bureau13 wrote:
OK, working on the least intrusive (and admittedly least effort) tests first.

I disconnected the wastegate control line from the top, and tried to pressurize it to see if it would hold. It does not. At all. It's wide open, not a "leak" but my hand vac pump couldn't pressurize it at all. I used an air compressor too, no dice.


That sounds very bad as in your WG diaphragm or line is blown wide open..

bureau13 wrote:

It could also tend to support my preferred (because it doesn't involve me needing a new turbo) theory, that the wastegate is completely stuck open...I think? In that situation, pressurized air goes where after it forces open the wastegate...out the top port/vent? That's my assumption.


If the diaphragm in the WG is blown then yes, the pressurized air would go in the bottom port and then out the top port.

If the diaphragm is good and the valve guide is good the air put into the bottom port should go nowhere..
It is possible that the valve guide in the WG is so bad that the air leaks past that and into the exhaust pipes.

bureau13 wrote:

Sucks that the wastegate is such a pain to get to (no lift here). Might still make sense to remove that cover on the recirc valve on the turbo, just to see what's there. However, I'm wary of causing additional issues, and that wouldn't explain the issue with the wastegate/control line. So maybe since I know there's something wrong there, I just need to take that out and inspect it (and fix it) before moving to the next item...


Yep it sucks a bit.. It really sucks that diaphragms are like $120 too..
The WG is a 930 WG so they are expencive but are often rebuilt. Plan to replace all of the studs in it..

One good thing is that their is a Tial WG that is a direct bolt on replacement for the 930 WG so if your WG is very screwed up you can just easily replace it with a Tial..
https://www.vividracing.com/tial-f46-46mm-wastegate-for-porsche-911-turbo-7594-p-151577.html
About $480 on Ebay new..

If you go to completely remove the WG line note that it is bolted to the back of the head too on one of the distributor/water housings..


To pull the WG, pull the J-pipe, pull the downpipe/exhaust, pull the WG mount to the torque tube, WG line banjo, WG is off..
Plan to replace the studs/nuts..

Pulling the downpipe will also give you access to the turbine wheel so you can play with it..
I do not think that you can get to the compressor wheel short of removing the compressor housing because of the complicated 931 compressor housing..

If you have the WG off you have the Turbo 1/2 off so that's a bonus..

Cleaning out and replacing the gaskets on the recirc valve is a very good idea.. My original gaskets looked like crushed rock candy.
I replaced mine with hand made leather gaskets..

The recirc valve is extremely simple so you don't have to worry much about screwing it up.. It is just a spring and a piston but possible to put back together backwards so note which direction and end the piston goes in, and spring, and which cap is which and which direction the one with the line goes on gets clocked correctly.
_________________
80 Turbo - Slightly Modified
Back to top
View user's profile Send private message Yahoo Messenger
bureau13  



Joined: 07 Sep 2017
Posts: 304
Location: South Florida

PostPosted: Mon Feb 18, 2019 3:14 am    Post subject: Reply with quote

Good info here, thank you. Glad you mentioned about the wastegate line being attached to the head...I'll look for that.

Do you think there is any performance advantage to going with a Tial over rebuilding my stock wastegate (or sourcing a rebuilt 930 wastegate)?

I think while it's out I will add the fitting to the top port for use with some sort of boost controller. May as well...

Fasteddie313 wrote:
bureau13 wrote:
OK, working on the least intrusive (and admittedly least effort) tests first.

I disconnected the wastegate control line from the top, and tried to pressurize it to see if it would hold. It does not. At all. It's wide open, not a "leak" but my hand vac pump couldn't pressurize it at all. I used an air compressor too, no dice.


That sounds very bad as in your WG diaphragm or line is blown wide open..

bureau13 wrote:

It could also tend to support my preferred (because it doesn't involve me needing a new turbo) theory, that the wastegate is completely stuck open...I think? In that situation, pressurized air goes where after it forces open the wastegate...out the top port/vent? That's my assumption.


If the diaphragm in the WG is blown then yes, the pressurized air would go in the bottom port and then out the top port.

If the diaphragm is good and the valve guide is good the air put into the bottom port should go nowhere..
It is possible that the valve guide in the WG is so bad that the air leaks past that and into the exhaust pipes.

bureau13 wrote:

Sucks that the wastegate is such a pain to get to (no lift here). Might still make sense to remove that cover on the recirc valve on the turbo, just to see what's there. However, I'm wary of causing additional issues, and that wouldn't explain the issue with the wastegate/control line. So maybe since I know there's something wrong there, I just need to take that out and inspect it (and fix it) before moving to the next item...


Yep it sucks a bit.. It really sucks that diaphragms are like $120 too..
The WG is a 930 WG so they are expencive but are often rebuilt. Plan to replace all of the studs in it..

One good thing is that their is a Tial WG that is a direct bolt on replacement for the 930 WG so if your WG is very screwed up you can just easily replace it with a Tial..
https://www.vividracing.com/tial-f46-46mm-wastegate-for-porsche-911-turbo-7594-p-151577.html
About $480 on Ebay new..

If you go to completely remove the WG line note that it is bolted to the back of the head too on one of the distributor/water housings..


To pull the WG, pull the J-pipe, pull the downpipe/exhaust, pull the WG mount to the torque tube, WG line banjo, WG is off..
Plan to replace the studs/nuts..

Pulling the downpipe will also give you access to the turbine wheel so you can play with it..
I do not think that you can get to the compressor wheel short of removing the compressor housing because of the complicated 931 compressor housing..

If you have the WG off you have the Turbo 1/2 off so that's a bonus..

Cleaning out and replacing the gaskets on the recirc valve is a very good idea.. My original gaskets looked like crushed rock candy.
I replaced mine with hand made leather gaskets..

The recirc valve is extremely simple so you don't have to worry much about screwing it up.. It is just a spring and a piston but possible to put back together backwards so note which direction and end the piston goes in, and spring, and which cap is which and which direction the one with the line goes on gets clocked correctly.

_________________
-----------------------------------------
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: 2034
Location: MI

PostPosted: Mon Feb 18, 2019 7:39 am    Post subject: Reply with quote

bureau13 wrote:

Do you think there is any performance advantage to going with a Tial over rebuilding my stock wastegate (or sourcing a rebuilt 930 wastegate)?


No..
No performance gain either way I wouldn't think but it might be cost effective..
A brand new tial is about the same price as a used 930 WG that likely needs rebuilt..

930 WG valve guide $100
930 WG diaphragm $150
+ $ for all new studs and nuts
+ $ or time extracting broken broken studs if you aren't super lucky.. I spent a lot of time extracting broken studs.

Then your rebuilt 930 WG is worth good money so is probably a good investment..

But if you can find a good deal on a lightly used tial f46 WG it might be easiest/cheapest..

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/486071-best-wastegate.html
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/782170-wastegate-hammered.html

I think it used to be that replacement valve guides had to be made but now their is one on ebay, and the diaphragms used to be impossible to find but now can be had but quite expensive at $100-$150 so it's a toss up..

If you search ebay for "46 wastegate" Their are a lot of 46mm WGs with 4 bolt flanges but I don't know if the 4 bolt pattern is an exact fit like the Tial..
Some very cheap china ones are available they may fit but who knows how well they might work or not and for how long..

bureau13 wrote:

I think while it's out I will add the fitting to the top port for use with some sort of boost controller. May as well...


I would definately do that and run a hose from it up top to where you can get at it if/when you ever want to use it..

The top port has some strange metric thread.
Some 931s have a banjo in the top port already for you to put a hose on that makes it real nice and easy.. Some 931 top ports have a mushroom thing that you will have to replace with a barb or banjo to put a line on the top port..
Definately a good "while you are in there" thing to do..

bureau13 wrote:

I disconnected the wastegate control line from the top, and tried to pressurize it to see if it would hold. It does not. At all. It's wide open, not a "leak" but my hand vac pump couldn't pressurize it at all. I used an air compressor too, no dice.


Note that some leakage past the valve guide from the bottom port is acceptable but shouldn't be "wide open"..
A small hand pump might not do it but if your air compressor won't cycle it their is definitely something wrong..
_________________
80 Turbo - Slightly Modified
Back to top
View user's profile Send private message Yahoo Messenger
bureau13  



Joined: 07 Sep 2017
Posts: 304
Location: South Florida

PostPosted: Thu Feb 28, 2019 1:47 am    Post subject: Reply with quote

UPDATE

So this is weird...I still haven't been able to get the car up and inspect the wastegate...the 928 is off getting painted so I need this car to stay running...but suddenly yesterday, I had boost. As quickly as it went away, it came back. I don't get it. It's overboosting just as before, btw (which may actually be a previous owner's intent, since the overboost switch is disconnected and the wire to it grounded).

I think the stuck wastegate theory is still possible. Possibly also the stuck recirculating valve in the turbo, although I will blow some compressed air down the boost control line and see if I get different results now.

The one theory that I hope is incompatible with this is the coked-up turbo. Has anyone ever seen one magically start working, like nothing was ever wrong, after failing for this reason?
_________________
-----------------------------------------
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: 2003
Location: Somerset, UK

PostPosted: Thu Feb 28, 2019 5:28 am    Post subject: Reply with quote

Sounds like a WWII grenade with a rusty pin..........you know its going to go bang in your hand, but just don't know when
_________________
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: 304
Location: South Florida

PostPosted: Thu Feb 28, 2019 5:45 am    Post subject: Reply with quote

That's a pretty ominous analogy, but, yeah. Pretty much!

Carrera RSR wrote:
Sounds like a WWII grenade with a rusty pin..........you know its going to go bang in your hand, but just don't know when

_________________
-----------------------------------------
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
Display posts from previous:   
Post new topic   Reply to topic    924Board.org Forum Index -> 931 Tech. All times are GMT + 10 Hours
Goto page Previous  1, 2
Page 2 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