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1984 308 QV still slight mis

Discussion in 'Technical Q&A' started by funshipone, Jun 18, 2005.

  1. funshipone

    funshipone Formula Junior

    Jan 2, 2002
    618
    Harrison Twp. Mi. US
    Full Name:
    John Bicsak
    Well replaced following wirers, plugs, coil wire, injectors, mechanic said distributors looked good, also replaced muffler all of cat was inside muffler made big diffrerence on power, but still have slight miss at constant RPM say at 3000 or 4000 acceleration excellent. Mechanic checked diplex connections good ground. What is left going nuts, miss is just enough to be noticed and a pain.
    When idleling you can hear at exhaust pipe miss every other milesecond or so just little tick tick.

    Ok men who wins with correct answer?

    I appreciate all your input, thank you going nuts Ferrari owner.
     
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  3. matteo

    matteo F1 World Champ

    Aug 1, 2002
    13,748
    On a plane somewhere
    Full Name:
    Heir Butt
    Did you replace the plug extenders? Sometimes they burn a whole in them and then arch to the block.
     
  4. funshipone

    funshipone Formula Junior

    Jan 2, 2002
    618
    Harrison Twp. Mi. US
    Full Name:
    John Bicsak
    Yes they replaced plug extenders. Yes some of them were cracked.
     
  5. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,687
    North shore, MA
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    THE Birdman
    Pull the connectors off all three flywheel sensors and check the resistance with an ohm meter. They should all be in the neighborhood of 600 ohms. If one is toast, it typically fails with an open circuit. Strangely, even when they are toast, they often still give just enough signal that the engine will still run, but it will miss as the signal is barely above the noise, and the ignition ECU will screw up interpreting it. If the tach does something funky when the engine misses, it's on the side of the engine that is run by the ECU with the tach on it. If the tach doesn't do anything funky, start with the side that doesn't run the tach. Had this problem on my Mondial recently. The 1-4 bank TDC sensor went. Tach runs off 1-4 on the Mondial, and an Fchat friend noticed the correlation between the miss and the tach freaking out. That was what gave me the clue to start at the ECU and work backwards from there. If it had been on the other ECU, the problem would have been much harder to find.

    Birdman
     
  6. Darolls

    Darolls F1 Veteran
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    Jul 2, 2003
    6,799
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    Sparky
    Could be a coil or sticky injector.
     
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  8. funshipone

    funshipone Formula Junior

    Jan 2, 2002
    618
    Harrison Twp. Mi. US
    Full Name:
    John Bicsak
    I will take my car back to Cauley Ferrari where they just replaced muffler have them check fly wheel sensors. I was wondering for my own knowledge where are sensors located can I see them from above or must I get underneath the engine to reach and see them, are they on right or left side.
    I really appreciate everyones input like I said before first time in five years car has given me any problems.
    I was planning on taking in this fall for belts and tune up.

    Where is best place to purchase sensors rough cost.
     
  9. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,687
    North shore, MA
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    THE Birdman
    John,
    The engine I have experience with is the one in the Mondial QV, which I'm pretty sure has the sensors in the same place as a 308 QV. If you remove the driver's side rear wheel and well liner, you will be staring at the bellhousing. The sensors are located around the outside of the bellhousing in line with the flywheel at about the 11 o'clock, 1 o'clock and 7 o'clock positions. Each one has two leads on a connector that is pretty simple to take apart once you figure out how to pry the little locking clip off. Then you can measure their resistance easily.

    I ordered a replacement from Ferrari UK at £44 or about $80. Not cheap, but the cheapest source I found. Even with shipping it was cheaper than Rutlands.

    Good luck

    Birdman
     
  10. Harta320

    Harta320 Karting

    Nov 6, 2003
    169
    Sarasota, FL
    Full Name:
    Bill Smith
    I have the exact same problem at idle. The car runs great at all rpms with no misses but at idle there is a small tick that just drives me crazy. My car also runs a little rich at idle and we can't seem to lean it out. Hopefully the 2 are related. I have changed or checked just about everything but these sensors. I have not been able to work on this problem for over a month now because I am getting a shock rebuilt but this may be the answer to my problem. What do you think Birdman?

    Oh Yea, How much and where do you get these senors?

    Thanks
    Bill Smith
     
  11. funshipone

    funshipone Formula Junior

    Jan 2, 2002
    618
    Harrison Twp. Mi. US
    Full Name:
    John Bicsak
    Thank you very much I will investigate maybe by chance one of the connectors is just not making good contact. I again say this is a wonderful site.
     
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  13. gil308

    gil308 Formula 3

    Jun 22, 2004
    1,957
    Charleston, SC
    Full Name:
    Gil
    If all else fails, rejet the injectors...workef for me (well, my mechanic).
     
  14. funshipone

    funshipone Formula Junior

    Jan 2, 2002
    618
    Harrison Twp. Mi. US
    Full Name:
    John Bicsak
    Injectors were replaced with everything else. I jacked up left rear removed inner fender found sensors to hard to reach with only being on jack and support. I will take to Cauley Ferrari tomorrow have them check out sensors.
     
  15. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,687
    North shore, MA
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    THE Birdman
    John,
    You don't need to get at the sensors themselves to check them. Each sensor has about a 12" wire on it, with a 2 pin connector at the end. The connectors are held in a bundle that is easy to get to. Not sure where they bundle them on a 308, but it should be easy to find. Simple ohm meter across each of the sensors and you can quickly determine if they are OK.

    If you end up needing to replace a sensor, two of the three sensors are pretty easy to get at, but the forward one is a pain.

    Birdman
     
  16. mlm

    mlm Rookie

    Sep 23, 2011
    3
    Pickens, SC
    Full Name:
    Michael L Miller Jr.
    My 85 308 will run fine for a little while then it seems to be running on four cylinders. The tachometer seems to be connected to this issue as it comes and goes also. I would love to get this fixed, any help would be very appreciated.
     
  17. Darolls

    Darolls F1 Veteran
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    Jul 2, 2003
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    Sparky
    #14 Darolls, Sep 24, 2011
    Last edited: Sep 24, 2011
    Check the digiplexs located in the rear compartment left side under the carpet(the luggage compartment behind the engine). Water can get in there and corrode the connections.

    You can reverse connections at the coils to find out which bank is causing the problem. If the problem changes from one bank to the other, clean the connectors and then coat the outside of the connectors with silicone grease to prevent further moisture intrusion.
     

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