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Technical SBC runs and sputters for 10 seconds after keys shut off...

Discussion in 'The Hokey Ass Message Board' started by RIBONES, Dec 21, 2015.

  1. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    The key gets shut off and the motor wants to keep going. I understand my car likes it when I run her, but baby I'm done, I gotta go.
    I just replaced my key and ignition thinking that was the problem, but it's not. I'm sure it's not the wiring because that's a fairly new wiring harness and I'm sure I did it all correctly. Plus it still shuts off after 5 or so seconds. The alternator is brand new also. The next thing I would think is the carburetor? It an older Rochester Quadrajet, but I'm not too savvy on carbs. I did some research but all I found on here was wiring problems, and I'm pretty sure that's not the case. I could be wrong, I have been before.

    Any suggestions? Thanks in advance.
     
  2. My 38 Chevy did that because the electric radiator fan was wired without a relay. When I turned the key turned off the fan keeps spinning, and changes from an electric motor to and generator, and creates enough current to keep the car running for 5-10 seconds.
     
    LOU WELLS likes this.
  3. bonzo-1
    Joined: Oct 13, 2010
    Posts: 342

    bonzo-1
    Member

    Check your timing if its run on (dieseling)
    Or the alternator may be feeding the ignition.
    Had another one that the electric fan would generate voltage as it spun down.
     
  4. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,217

    2OLD2FAST
    Member
    from illinois

    Is it "running" or deiseling ??
    dave
     

  5. Octane too low?........Coil on its' way out?
     
  6. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,770

    olscrounger
    ALLIANCE MEMBER

    check timing and idle speed
     
  7. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

    Yes, this is a real thing. Disconnect electric fan and see if problem goes away.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,944

    squirrel
    Member

    is the idle speed too high?
     
    saltflats likes this.
  9. Sounds like engine run on. Aka dieseling. In my experience it's generally one of two things. Timing or carbon build up in the combustion chambers. I would start by trying to clean out the carbon. I like to do this by using either water or a product called Seafoam. The way I do it is, get the rig warmed up and while it's running, trickle water or Seafoam down the carb. You will have to modulate the throttle to keep it running. Be careful to not pour to much at a time or you will hydrolock the engine...And it's gonna produce a huge steam or smoke show out the exhaust. So be warned. You may need to repeat this a few times. I find Its rarely the timing but it has been for me once or twice. So if you are still having issues after this check the timing.
     
  10. bchctybob
    Joined: Sep 18, 2011
    Posts: 5,190

    bchctybob
    Member

    Hitchhiker, does that really work? My Dad used to do that periodically to his old cars ('49 Ford and '51 Stude), said it steamed out the carbon. He used water. Ever look inside and see what it did?
     
  11. bchctybob
    Joined: Sep 18, 2011
    Posts: 5,190

    bchctybob
    Member

  12. Seems to. I've fixed a few run on issues that way.
     
  13. Also touching base on the "idle speed" suggested. Again just generally... if the idle speed or mixture is off. That will cause carbon build up. Simply adjusting that won't cure the problem as you still have carbon hot spots trying to ignite the mixture. It will prevent it from happening again. But it's not technically what is causing the run on.
     
  14. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    FWIW, chevy actually used an anti-dieseling solenoid on some seventies era 350s straight from the factory. IIRC it was an emissions deal because they had to open the throttle plates more at idle to help compensate for the ultra lean IFR calibration...
     
    metlmunchr, saltflats and Hitchhiker like this.
  15. Dieseling or continuing to run a lil after key is off? Carb /timing, or electrical bleed. A lil more info will help the diagnose..........
     
    EZStreetRods likes this.
  16. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    You guys are awesome. Barely an hour has gone by and this is all the responses. I love the hamb.
     
  17. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    When I get back, Ill disconnect the fan first and see if that has anything to do with it. My pops always said go for the smallest fix first. If that does nothing I'll pour some water down the carb. That sounds like fun. As far as info in the motor..it's a newer rebuilt 350. New electrical wiring, fan, alternator. All 12 volt.
     
  18. 9 times out of 10 is simply an idle that's too high. Adjust the idle speed down and try it again.
     
    Hitchhiker and squirrel like this.
  19. Was this car running and driving and then this all happened or new build?
     
  20. Do what Pop said first.........
     
  21. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    Holy freakin moly batman! GEARHEADRUSS you nailed it. I appreciate everyone and their imput, you guys are all awesome. But RUSS, you called it.
    i disconnected the fan and it shut right off!!!
    I thought that was too easy, so I hooked the fan back up. It Wouldn't shut off for a good 10 seconds.
    Unhooked it again and she shut off right away.

    Russ I owe you a case of beer. Now I just gotta figure out how to hook up a relay to it...hmmm...
     
  22. JOECOOL
    Joined: Jan 13, 2004
    Posts: 2,771

    JOECOOL
    Member

    Always, Always , Always put a relay in a fan circuit.
     
  23. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

    Well I for one am glad you didn't pour a bunch of water down the carburetor first.
     
    RIBONES likes this.
  24. DualQuad55
    Joined: Mar 5, 2005
    Posts: 1,382

    DualQuad55
    Member
    from NH

    Relays are actually very easy to install/hook up. I assume you have your fan switched on using 12v positive feed, and the fan is constantly grounded.
    What you need to do is get a 4 wire relay and connector (although you can use insulated female spade connectors to attach to the relay if you can't get a connector.
    You run one wire to constant ground, one wire to constant 12v such as battery or accessory output. so long as it is fused or on a circuit breaker.
    One wire is from you switch that activates the fan now, and the last wire goes to the fan itself.
    Basically you interrupt the circuit with the relay, ground the relay and add a power source.


    Here is a quick google search for a diagram. If using a 4 wire relay omit the 87a circuit.
    [​IMG]
     
    scrap metal 48 likes this.
  25. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    Thank you Dual55, hitchhiker, Russ, and all. I appreciate the help!
     
  26. Now Now- play nice with everyone when "I gotta buy you beer" Glad you got it handled. The relay is straight forward as pictured above...... Just send the lady in your avatar over and we'll be even.....LOL!
     
  27. you will also need a temperature switch that will be installed in a place where it can monitor the water temperature. If you SBC is a and older one like a 283 or 327 then the fan should turn on when the water gets to 180 or 190 and stay on till the car cools down to 150-160 . I'm glad DualQuad55 helped with the wiring.
    Temp sender.jpg
     

    Attached Files:

  28. Edited;

    Do not wire the relay terminal 87A to ground as shown in the above picture, it will be a direct short and will blow the fuse for your fan power supply. Terminals 87A and 30 have continuity when the relay coil is not receiving power. Fused battery voltage should be coming in at pin 30 and your fan wire to 87. The diagram is half right.
     
    Last edited: Dec 21, 2015
    Donald A. Smith likes this.
  29. RIBONES
    Joined: Apr 7, 2008
    Posts: 45

    RIBONES
    Member
    from DAGO ca

    Where would you recommend a good place be?
     
  30. If you have newer cylinder heads (like the kind with bolt holes in the ends of the heads) then there should be a threaded hole in-between the number 1 and 3 spark plugs or on the passengers side in-between the 6 and 8 plugs. If you have older heads those holes wont be there. Then you need to install it in the intake manifold near the thermostat. There are some thermostat housings that have a place to add a temp sender for a gauge. There are also other types of water temperature switches that can be put in the fins of the radiator. I prefer the type that actually makes contact with the water so it gets an accurate reading.
     

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