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1981 931, all of a sudden car seems like it is running rough

 
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canyonblaster  



Joined: 20 Aug 2012
Posts: 391
Location: Denver, CO, USA
PostPosted: Mon Jun 20, 2016 4:39 am    Post subject: 1981 931, all of a sudden car seems like it is running rough Reply with quote
feels like it is running at redline when it is is only at 4K RPM? Argh...
Any ideas? Thx!

BTW, I wonder if the ambient heat is responsible. 95 F here and high altitude (Denver CO).
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PCA Licensed Club Racer & Driving Instructor Current P cars: 1981 931
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morghen  



Joined: 21 Jan 2005
Posts: 8883
Location: Romania
PostPosted: Mon Jun 20, 2016 5:19 am    Post subject: Reply with quote
boost leak?
If its an S2, the TB oring has softened up and got spewed out?
That happend to mine.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2309
Location: Somerset, UK
PostPosted: Mon Jun 20, 2016 6:58 am    Post subject: Reply with quote
Fuel blockage/leaning out
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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
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11723
Location: PacNW
PostPosted: Mon Jun 20, 2016 1:46 pm    Post subject: Reply with quote
Immediate wideband, please.
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canyonblaster  



Joined: 20 Aug 2012
Posts: 391
Location: Denver, CO, USA
PostPosted: Tue Jun 21, 2016 3:12 am    Post subject: Reply with quote
morghen wrote:
boost leak?
If its an S2, the TB oring has softened up and got spewed out?
That happend to mine.


Please clarify what this is? Thanks!
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PCA Licensed Club Racer & Driving Instructor Current P cars: 1981 931
Past P cars, 1985 944, 1987 951, 1990 911 C4, 2002 Boxster S, 2005 996 GT3, 2013 911 C2S
Daily Driver P cars: 2008 Cayenne GTS, 2013 Cayenne GTS
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canyonblaster  



Joined: 20 Aug 2012
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Location: Denver, CO, USA
PostPosted: Tue Jun 21, 2016 3:13 am    Post subject: Reply with quote
Rasta Monsta wrote:
Immediate wideband, please.


Rasta, can my shop likely test that?
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PCA Licensed Club Racer & Driving Instructor Current P cars: 1981 931
Past P cars, 1985 944, 1987 951, 1990 911 C4, 2002 Boxster S, 2005 996 GT3, 2013 911 C2S
Daily Driver P cars: 2008 Cayenne GTS, 2013 Cayenne GTS
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canyonblaster  



Joined: 20 Aug 2012
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Location: Denver, CO, USA
PostPosted: Tue Jun 21, 2016 3:14 am    Post subject: Reply with quote
Carrera RSR wrote:
Fuel blockage/leaning out


Gas tank, all fuel pumps and filters are new,recent. When sitting idling, engine revs fine.
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PCA Licensed Club Racer & Driving Instructor Current P cars: 1981 931
Past P cars, 1985 944, 1987 951, 1990 911 C4, 2002 Boxster S, 2005 996 GT3, 2013 911 C2S
Daily Driver P cars: 2008 Cayenne GTS, 2013 Cayenne GTS
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW
PostPosted: Tue Jun 21, 2016 3:48 am    Post subject: Reply with quote
canyonblaster wrote:
Rasta, can my shop likely test that?


I suppose, but it would still require installing a pre-cat wide band O2 sensor, and testing under load. Adding an AFR gauge is a better long term solution.
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK
PostPosted: Tue Jun 21, 2016 7:15 am    Post subject: Reply with quote
canyonblaster wrote:
Carrera RSR wrote:
Fuel blockage/leaning out


Gas tank, all fuel pumps and filters are new,recent. When sitting idling, engine revs fine.


It will, the engine is not under load. Either air is getting in causing it to lean or fuel is being restricted and going lean

As rasta says, an AFR gauge will tell you if it's lean or rich under load. Best rested on rolling road.

Assume boost is OK too? If it's over boosting then the overboost switch kicks in by cutting the fuel pump. Again leaning it out.
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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
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canyonblaster  



Joined: 20 Aug 2012
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Location: Denver, CO, USA
PostPosted: Tue Jun 21, 2016 8:11 am    Post subject: Reply with quote
Thanks guys. What is the TB O Ring?
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Kenodog  



Joined: 25 Jun 2003
Posts: 2651
Location: Vancouver,B.C.
PostPosted: Tue Jun 21, 2016 10:51 am    Post subject: Reply with quote
The TB O-ring is the throttle body o-ring. On S2 cars there is a rubber o-ring that theoretically seals between the throttle body itself and the charge tube. All kinds of nastiness can happen to them over the years. Replacement Viton ring is about $6 and is another check mark on the list of cheap and easy things to do to have a reliable 931.



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canyonblaster  



Joined: 20 Aug 2012
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Location: Denver, CO, USA
PostPosted: Thu Jun 23, 2016 6:58 am    Post subject: Reply with quote
I suspected it was heat soak or vapor lock. Weather is nice and cool today, 80 F. I vented the gas gap, added some fuel (it wasn't empty but was low), and the car drove like a top today! Yahoo!
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PCA Licensed Club Racer & Driving Instructor Current P cars: 1981 931
Past P cars, 1985 944, 1987 951, 1990 911 C4, 2002 Boxster S, 2005 996 GT3, 2013 911 C2S
Daily Driver P cars: 2008 Cayenne GTS, 2013 Cayenne GTS
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