HELP! 1984 308 Keeps Shutting Itself Off While Driving

Discussion in 'Technical Q&A' started by Dr Tommy Cosgrove, Dec 4, 2017.

  1. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Two Time F1 World Champ
    Rossa Subscribed Owner

    May 4, 2001
    25,973
    Birmingham, AL
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    Tommy
    This happened to me once last summer on I-20 at speed and it spooked the hell out of me but it started right back up again on the side of the road. I was just outside of Atlanta on the way home and it made it back just fine. I honestly had forgotten about it - until yesterday and it returned with a vengeance. On a 70 mile drive with a local car club, the engine would just shut itself off. It was like you turned the key off. The electrical system was still working. The radio would still be on, the lights would work and the dash lights would operate , but the engine would just die and not start for a few seconds. I could get it to restart by pushing the clutch pedal in and letting it back out while I was on the move a few times. I was even able to restart it on the fly with the clutch in using the key again. It would restart and I just let the clutch back out and keep driving. A few other times I had to sit on the side of the road for no more than 10 seconds and it would start and run again.

    A few things:

    When it was running, it ran great. No misses, no power loss. Smooth and perfect.

    When it shut down, it would just die. No backfire, now preliminary power loss, no hiccough whatsoever, just instantly off. Period. Absolutely no warning. Just off. Dash light all on, radio playing but engine off.

    When it started again, it would start instantly and run perfectly. Just like it is supposed to as if there was no problem at all and it would pull away with full power again. Absolutely no hesitation to start and no rough or stumbling idle.

    One thing I did notice and I don't know if this means anything but when the engine died, the tach would still be matching the engine revs (I would still be in gear at about 50 or 60 mph when it did it) In other words when the engine shut down the tach would still be where it was running and as the car slowed and it would gradually go down as the car slowed. I would have expected to see the tach fall to zero when the engine shut off but it didn't.

    It seemed to like being above 4500 rpm. I was able to get where we were going by keeping the revs up high like that.

    We have a tow truck follow us on our drives so I got it back home that way. Of course it started fine and I drove it up on the flatbed. As I was sitting there on the back of the truck idling, it died again. After the car was dropped off at my house, it started fine and I drove it back off the truck, down the driveway and in the garage without a problem.

    Any ideas? Since the engine runs great (when it is running) I am relatively comfortable this isn't a "serious" problem. I am going to get it up to Ron in Atlanta but I wanted some Fchat input in the meantime.
     
  2. Kaivball

    Kaivball Three Time F1 World Champ
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    Jan 11, 2007
    33,577
    Kalifornia
    Sounds electrical. Something with the ignition switch?

    Kai
     
  3. G. Pepper

    G. Pepper F1 Rookie
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    Mar 15, 2012
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    George Pepper
    Sounds like it is simply losing the spark.
     
  4. smg2

    smg2 F1 Veteran
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    Apr 1, 2004
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    I'd check the ignition switch electrics as well. First though check the battery voltage at idle and 2k rpm.
     
  5. tbakowsky

    tbakowsky F1 World Champ
    Professional Ferrari Technician Consultant

    Sep 18, 2002
    12,535
    The Cold North
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    Howie Felterbum
    Crank sensor
     
  6. robbie

    robbie F1 Rookie
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    Aug 26, 2005
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    You said it was like the key being turned off ... so I'd suspect the ignition switch.
     
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  8. tf308

    tf308 Formula 3
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    Dec 14, 2003
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    Tim
    Mine died once...

    It was the fuel pump relay in the dash.

    If that's out...no power to your pump.


    Sent from my iPhone using FerrariChat
     
  9. tf308

    tf308 Formula 3
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    Hard for me to think it's ignition related because it will definitely run and even start with one side completely out. Chance of double intermittent failure seems low.


    Sent from my iPhone using FerrariChat
     
  10. tf308

    tf308 Formula 3
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    Dec 14, 2003
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    Tim
    If it were a crank sensor....it would have to be the rpm sensor that both boxes share.

    Test the resistance of the sensor at the digiplex harness


    Sent from my iPhone using FerrariChat
     
  11. tbakowsky

    tbakowsky F1 World Champ
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    Sep 18, 2002
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    Howie Felterbum
    Pardon me..yes you are correct. Those things have run me over the bend a few times.
     
  12. finnerty

    finnerty F1 Veteran
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    May 18, 2004
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    #11 finnerty, Dec 7, 2017
    Last edited: Dec 7, 2017
  13. tf308

    tf308 Formula 3
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    Tim
    Finnerty, have you had trouble with the frequency valve ? Would love to hear more. How did you test it or verifying?


    Sent from my iPhone using FerrariChat
     
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  15. finnerty

    finnerty F1 Veteran
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    It is a common failure mode on cars running the Bosch FI with frequency valve. I've seen it many times on several makes (not just Ferrari) which share the component.

    There is an impedance value you can check with a proper DMM, as well as a more complicated pressure delta measurement which can be measured ---- the various Bosch technical manuals contain the test specifications and values. But, generally, it is an obvious failure to detect just by observing that it is no longer "buzzing" (rapidly pulsing off/on) with the engine running at various RPMs.

    The symptoms Tom is experiencing with his car are consistent with a failed frequency valve, but as others have noted, it could be several other possibilities too.

    It is just that given his car's age, the frequency valve is the first thing I would rule in / out before looking at other things. It is very easy to do, and has a high probability of being the fault.
     

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