Page 1 of 3 123 LastLast
Results 1 to 10 of 23

Thread: Misfire every 5 seconds

  1. 09-21-2018, 06:46 PM #1
    Boulder Bob
    Boulder Bob is offline
    Senior Member Boulder Bob's Avatar
    Join Date
    Dec 2003
    Posts
    207

    Misfire every 5 seconds

    I have a very strange misfire - it happens exactly every 5 seconds. I posted a YouTube - search for "Bob's 911 Misfire".

    Has anyone ever experienced anything like this? I have gone through a lot of testing of ignition and some fuel system items already -

    Thanks for the help.
    73 911S Targa
    Reply With Quote Reply With Quote
  2. 09-21-2018, 11:09 PM #2
    62S-R-S
    62S-R-S is offline
    Senior Member 62S-R-S's Avatar
    Join Date
    Nov 2009
    Location
    Cecil pa
    Posts
    861
    Guessing you've already done a casual test with carb cleaner, at a few locations to try to rule out vacuum issues.
    Reply With Quote Reply With Quote
  3. 09-22-2018, 04:48 AM #3
    Boulder Bob
    Boulder Bob is offline
    Senior Member Boulder Bob's Avatar
    Join Date
    Dec 2003
    Posts
    207
    Quote Originally Posted by 62S-R-S View Post
    Guessing you've already done a casual test with carb cleaner, at a few locations to try to rule out vacuum issues.
    Have not, but will try that - thanks
    73 911S Targa
    Reply With Quote Reply With Quote
  4. 09-22-2018, 04:50 AM #4
    Robert5995
    Robert5995 is offline
    Senior Member
    Join Date
    Apr 2011
    Posts
    638
    Bob -

    Seems like a rich/lean mixture surge. Does it do it cold and hot?

    - Rob in boulder
    Reply With Quote Reply With Quote
  5. 09-22-2018, 05:17 AM #5
    Frank Beck
    Frank Beck is offline
    Banned
    Join Date
    Nov 2004
    Location
    Scottsdale, AZ
    Posts
    9,752
    What's your CO at? Idle and high speed?

    There's a reason the factory manual has that procedure in there.
    Reply With Quote Reply With Quote
  6. 09-22-2018, 05:53 AM #6
    Boulder Bob
    Boulder Bob is offline
    Senior Member Boulder Bob's Avatar
    Join Date
    Dec 2003
    Posts
    207
    Quote Originally Posted by Robert5995 View Post
    Bob -

    Seems like a rich/lean mixture surge. Does it do it cold and hot?

    - Rob in boulder
    Runs worse cold - when warmed up it it starts the strange "every 5 seconds" misfire (rpm drop)
    73 911S Targa
    Reply With Quote Reply With Quote
  7. 09-22-2018, 05:55 AM #7
    Boulder Bob
    Boulder Bob is offline
    Senior Member Boulder Bob's Avatar
    Join Date
    Dec 2003
    Posts
    207
    Quote Originally Posted by Frank Beck View Post
    What's your CO at? Idle and high speed?

    There's a reason the factory manual has that procedure in there.
    great idea - just need a CO meter! will see if I can run this test

    thanks
    73 911S Targa
    Reply With Quote Reply With Quote
  8. 09-22-2018, 06:16 AM #8
    Frank Beck
    Frank Beck is offline
    Banned
    Join Date
    Nov 2004
    Location
    Scottsdale, AZ
    Posts
    9,752
    Quote Originally Posted by Boulder Bob View Post
    Runs worse cold - when warmed up it it starts the strange "every 5 seconds" misfire (rpm drop)
    Sounds WAY too lean.
    At least for now check dwell and timing.

    I love these posts...


    "Doc, please tell me why I'm coughing. Here's a 5 second video showing me coughing."
    Reply With Quote Reply With Quote
  9. 09-22-2018, 07:35 AM #9
    ejboyd5
    ejboyd5 is offline
    Senior Member ejboyd5's Avatar
    Join Date
    Dec 2010
    Location
    Southold, NY
    Posts
    821
    "Misfire?" Sharp "hiccup" in smoothness of firing or short duration drop in RPM regardless of throttle position?
    Reply With Quote Reply With Quote
  10. 09-22-2018, 09:28 AM #10
    edmayo
    edmayo is offline
    Senior Member
    Join Date
    Jul 2006
    Posts
    7,991
    Give us some history to work with, we can assume it didn't do this when new, so how long have you owned it, has it always done this since your ownership?, was there anything done just before this all started? did it just start suddenly one day? has anyone touched anything on the engine and then this symptom started right afterwards? Mechanic's rule of thumb, go to the last thing that was touched before problem occurred.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.
    Reply With Quote Reply With Quote
« Previous Thread | Next Thread »

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Forum Rules


Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.