365GT Ignition problem | FerrariChat

365GT Ignition problem

Discussion in 'Vintage (thru 365 GTC4)' started by TheMac, Jul 10, 2017.

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  1. TheMac

    TheMac Formula Junior

    Sep 5, 2009
    452
    Alberta
    Full Name:
    Jon Mac
    Sorry right away for the duplicate thread, I started this question in the Technical Q&A but someone suggested this might be the better sub-forum. My Dad's 365GT quit running last week (prior to that, it had not had a problem in years). Before the engine stopped, it sounded a bit lame, not like it was running rough, just kind of weak to my ear, and it was significantly down on power.

    We first investigated the fuel system. His car has the FISPA electrical pump and the autoflux, although with the FISPA running I don't believe the autoflux is operating, and it doesn't seem necessary. We verified that the carburetor bowls were full, and that the idle jets were squirting fuel.

    Next step was the ignition system. We attempted to verify that we are getting spark by attaching a timing light to the spark plug leads and cranking the engine. We got a puzzling result. No spark in 11 of the cylinders, but cylinder #3 for some reason seems to be sparking just fine. So far after that, we've removed the distributor caps to inspect/clean the points. That appears not to have had any effect; after putting it all back together, we still get spark on #3 and none of the other cylinders.

    Can anyone offer some assistance? Or at least suggest the next step? For reference, this is a dual distributor set up, and he has had MSD installed on it.
     
  2. MiuraP400

    MiuraP400 Formula Junior

    Feb 3, 2008
    939
    Arizona
    Full Name:
    Jim
    My favorite test is to pull the distributor caps off and measure the resistance from the post in the distributor cap to where the spark plug wire attaches to the spark plug. Ideally it should be about 10,000 ohms, but it can vary, anything in the 5000 ohms to 20,000 ohms will work and some wires (special case) are 0 ohms. Anything more than 20,000 needs to be corrected. Also test the coil wire lead. Test from the coil end to the carbon, you should see the same values. More often then not I find a lot of issues doing this test.

    Once that is good other issues to look for.
    Are you getting 12 volts to the coils?
    There are resistance checks you can do on the coils. On both the primary and secondary circuits. The correct resistances will depend on if your coils have ballast resistors or not and if the are high performance.
    Do a resistance check on the condenser's, assuming you have them with the MSD. Should be infinite.
    Since you have points, check the timing on cylinders 1, 6, 7, and 12. If all four points are in phase with each other and the timing is set correctly all four cylinders should give you the same reading. Note I am assuming your distributors have two sets of points in each one.

    Cheers Jim
     
  3. TheMac

    TheMac Formula Junior

    Sep 5, 2009
    452
    Alberta
    Full Name:
    Jon Mac
    We have figured out the problem and I thought I would update this thread just to bring some closure to it. I'll cut to the chase: It's not very exciting, but it was a bad battery. We did, of course, test the battery as soon as we figured it was a spark issue, and it tested at 12.8 volts. It would also crank the starter easily and for a long time. The battery was not dead, nor was it dying, but it also somehow was enough to turn the starter but not enough to produce the power to the MSD to give spark.

    We tested the coils, they tested fine, we tested the alternator, it tested fine, we tested the spark plug wires, they were fine. We had the wiring diagram to the MSD, which is actually two separate MSDs, one per bank. The trouble shoot there was fairly straightforward, but it just seemed really fishy that they would both fail at the exact same moment. So we went back to the beginning, to start again, and instead of just testing the battery, we swapped it for another that we already had. Car fired up easily, and after a minute or two, was running great.

    Thanks Jim for replying to this thread with advice on what to do next. Happy motoring.
     
  4. MiuraP400

    MiuraP400 Formula Junior

    Feb 3, 2008
    939
    Arizona
    Full Name:
    Jim
    Thank you for the update. It is always interesting to hear what fixed it. If it cranked over well, the battery is not the first thing you think of, nice work.

    Cheers Jim
     

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