81 SC sputtering/small backfires - Page 4 - Rennlist - Porsche Discussion Forums

Notices
911 Forum
Sponsored by:

81 SC sputtering/small backfires

 
Old 08-05-2009, 10:41 PM
  #46  
white99c2
User
 
white99c2's Avatar
 
Join Date: Aug 2009
Posts: 380
Default

No, mine had the grounds on them and were sparking. Did you blip the throttle a couple of times and look. Have you inspected the inside of the distributor cap and condition of the rotor.
Man I'll be honest with you, its like pissing in the wind trying to diagnose a problem like this.
Get the car to your wrench and have him connect it to a scanner. He will then get a visual how each of the 6 cylinders are running and know right away what is causing your problem. Read my last post, all those things contributed to my car running opposite to how it runs now. Our 911's need a tune-up every 10-12K miles to keep them running smooth.
white99c2 is offline  
Old 08-05-2009, 11:15 PM
  #47  
rusnak
I haddah Google dat
Rennlist Member
 
rusnak's Avatar
 
Join Date: Nov 2008
Location: Fresno, CA
Posts: 11,511
Default

I have this book. http://books.google.com/books?id=3q8...0scope&f=false

Toward the bottom, he mentions that an inductive timing light can be hooked up to make it like a poor man's scope.
rusnak is offline  
Old 08-06-2009, 11:03 PM
  #48  
aadrew10
User
Thread Starter
 
aadrew10's Avatar
 
Join Date: Jun 2009
Location: Palo Alto
Posts: 166
Default

I have found that the Bosch distributor that goes in an 81 SC is numbered 0 237 304 016. The number on mine is 0 237 303 003. I'm curious about which car this distributor was made for. I am starting to think my problems are because of this distributor and its inability to adjust the timing when under load, but before I replace it I want to make absolutely sure it is the root of the issue. Does anyone have any tips or tricks, or info about this particular model?

Your input is much appreciated.

- Andrew
aadrew10 is offline  
Old 08-06-2009, 11:28 PM
  #49  
rusnak
I haddah Google dat
Rennlist Member
 
rusnak's Avatar
 
Join Date: Nov 2008
Location: Fresno, CA
Posts: 11,511
Default

Why wouldn't you just hook up the timing light and check the advance against the curve chart?
rusnak is offline  
Old 08-06-2009, 11:38 PM
  #50  
aadrew10
User
Thread Starter
 
aadrew10's Avatar
 
Join Date: Jun 2009
Location: Palo Alto
Posts: 166
Default

The vacuum tubes on the distributor change the timing under load. When checking my timing in my driveway, the engine is not under load. This means the timing could be set correctly under a no-load condition, but would not advance properly under a loaded condition. This would explain why the engine runs well under no load, and sputters when accelerating. My distributor is unable to detect the loaded condition because of the lack of vacuum tubes, and would not give the required extra advancement. I talked a little about this in a previous post.

I am sure about none of this, it just seems logical to me. If anyone knows differently please let me know.

- Andrew
aadrew10 is offline  
Old 08-06-2009, 11:54 PM
  #51  
theiceman
Super User
 
theiceman's Avatar
 
Join Date: Aug 2005
Location: Cambridge Ontario Canada
Posts: 22,626
Default

hmm..looks likeit could be a distributor from a euro car

check this ,...

http://sites.google.com/site/e21323i...timing-numbers

interesting stuff really
theiceman is offline  
Old 08-07-2009, 12:03 AM
  #52  
rusnak
I haddah Google dat
Rennlist Member
 
rusnak's Avatar
 
Join Date: Nov 2008
Location: Fresno, CA
Posts: 11,511
Default

http://forums.pelicanparts.com/showthread.php?t=333640

Time to send Gunter a PM on the Pelican site. I'm not a CIS guy but I'd guess the vac advance gives the mech a little bit more advance off idle.
rusnak is offline  
Old 08-07-2009, 02:14 AM
  #53  
Lorenfb
Super User
 
Lorenfb's Avatar
 
Join Date: May 2003
Location: SoCal
Posts: 3,491
Default

"My distributor is unable to detect the loaded condition because of the lack of vacuum tubes, and would not give the required extra advancement."

Actually, a measurement of load generally retards the timing, i.e. to avoid
detonation and/or reduce emissions. Timing can be just based on a centrifugal
advance and given an advance marginal of safety to avoid detonation without
monitoring load via the intake vacuum. So having no vacuum input to a distributor
should not cause the problem here. Many early European and race engines didn't
have a vacuum input and the engines operated properly.

Most likely the problem results either from a weak spark, e.g. bad coil - silver,
or a lean mixture, e.g. low system pressure or too high of control pressure.
Both of these become significant under load. The coil wire spark should jump
about 15 to 25mm to ground. Also, if the rotor doesn't advance smoothly,
or if the shaft bushings are worn, the timing won't advance properly.

So, focus first on proper fuel pressures and then on proper spark and distributor
advance. Also, make sure that there are no intake air valves opening nor intake
air leaks occurring under load conditions.
Lorenfb is offline  
Old 08-11-2009, 09:24 AM
  #54  
Dave C 911sc
New User
 
Join Date: Aug 2009
Location: Twin Cities
Posts: 4
Default broken stud

My car has the same symptoms as yours and after going through everything (fuel and ignition) I FINALLY found an exhaust leak (which is what I originally thought this was) ...It is happening between the head and cylinder area of the rear most driverside cylinder. I havent pulled the cover yet to check, but I figure I most likely have a broken stud.
I know you mentioned that you looked for an exhaust leak, but did you look in the area where the head and cylinders meet?

Dave
Dave C 911sc is offline  
Old 08-11-2009, 11:24 AM
  #55  
aadrew10
User
Thread Starter
 
aadrew10's Avatar
 
Join Date: Jun 2009
Location: Palo Alto
Posts: 166
Default

Looking at cylinder 1 yesterday from below I noticed it seemed a bit oily. Could this be a sign of broken studs? Dave, it would be great if you could show a picture of this hard to find leak.

- Andrew
aadrew10 is offline  
Old 08-11-2009, 05:28 PM
  #56  
theiceman
Super User
 
theiceman's Avatar
 
Join Date: Aug 2005
Location: Cambridge Ontario Canada
Posts: 22,626
Default

naw .. all my base gaskets leak a little but my head stauds are fine and my engine piulls like an OX .. if you worry everytime you see an oil leak from your 911 your gona have fun
theiceman is offline  
Old 08-11-2009, 08:59 PM
  #57  
Houpty GT
User
 
Houpty GT's Avatar
 
Join Date: Apr 2007
Location: Along a road in South Carolina
Posts: 320
Default

Originally Posted by aadrew10 View Post
Looking at cylinder 1 yesterday from below I noticed it seemed a bit oily. Could this be a sign of broken studs? Dave, it would be great if you could show a picture of this hard to find leak.

- Andrew
Pull the lower valve cover to check for broken studs. Finding the leak can be tough because the leak will only occur under load which is when the high pressure causes the cylinder head to lift off the cylinder. This can also cause damage to both the head and the cylinder if left uncorrected. Pete has said that he never has seen a car with a leak that did not require machine work to repair. I have 10,000 miles on mine with no trouble. Some of the cars will show leakage staining at the cylinder and head where the leak is occurring but this is not the best way to check for broken studs since you may have damage by the time that happens.

You can take the opportunity to adjust your valve lash if you are so lucky to not have any broken studs but I think I am going to be 2 for 2 on this thread for my earlier recommendations from page one.
Houpty GT is offline  
Old 08-11-2009, 10:19 PM
  #58  
aadrew10
User
Thread Starter
 
aadrew10's Avatar
 
Join Date: Jun 2009
Location: Palo Alto
Posts: 166
Default

I will check all the studs this weekend. Houpty GT, in what context do you have 10,0000 miles on your car with no trouble? Is this since you discovered broken studs, or since you repaired them or...?

Is the best way to check studs by using a telescoping magnet AND trying to torque them to their specifications to see if they are loose?

- Andrew
aadrew10 is offline  
Old 08-12-2009, 12:22 AM
  #59  
Houpty GT
User
 
Houpty GT's Avatar
 
Join Date: Apr 2007
Location: Along a road in South Carolina
Posts: 320
Default

Originally Posted by aadrew10 View Post
I will check all the studs this weekend. Houpty GT, in what context do you have 10,0000 miles on your car with no trouble? Is this since you discovered broken studs, or since you repaired them or...?

Is the best way to check studs by using a telescoping magnet AND trying to torque them to their specifications to see if they are loose?

- Andrew
Generally they will fall out as soon as you take the cover off. I found I had some broken studs in the holes and I found them by using the magnet. I have 10,000 since my repair of the motor. I did not do any machining to the surface though my head and cylinder looked to be in very good condition. You will need to examine this area very closely. Some experts will insist on machining and others will not.

Do not try and retorque the head studs! During my motor disassembly, I had several studs break when I went to loosen the barrel nut. I would not question that these studs were probably terminally doomed to break but you may find yourself with a more broken studs if you tried to retorque the aged dilavar studs.

Good luck!
Houpty GT is offline  
Old 08-12-2009, 12:33 AM
  #60  
aadrew10
User
Thread Starter
 
aadrew10's Avatar
 
Join Date: Jun 2009
Location: Palo Alto
Posts: 166
Default

Thanks for the great advice. I am feeling pretty sure of what I will find when I do the check this weekend. Good thing I work in a machine shop
aadrew10 is offline  

Thread Tools
Search this Thread
Quick Reply: 81 SC sputtering/small backfires


Contact Us About Us Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: