308 distributor cap fault - probably | FerrariChat

308 distributor cap fault - probably

Discussion in '308/328' started by paul 308, Mar 25, 2011.

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  1. paul 308

    paul 308 Karting

    Jan 13, 2004
    110
    Guildford, Surrey UK
    Full Name:
    Paul Deslandes
    #1 paul 308, Mar 25, 2011
    I've convinced myself that the dizzy cap on my '76 euro spec, single distributor, points ignition, carb 308GTB is faulty, causing a misfire on one cylinder. I've changed around the plug, extender and HT lead and the problem stays with the cylinder which has good compression, equal to all the others, so I'm sure its not a cylinder related mechanical problem.

    With the plug out and laid on the engine it gives as good a spark as the others but in the engine it misfires continuously. I can't see anything obvious on the cap like a crack or signs of tracking and have cleaned it out with alcohol but to no good effect.

    Before I go out and buy a new one, for a price that makes your eyes bleed, does anyone know a fool-proof way of testing it or whether there's a way of making a temporary fix, such as spraying the inside with lacquer to seal any cracks? If I do something to the cap, however temporary, and it works even just for a few minutes, I'll know what I have to do.

    I'm pretty sure I'm going to end up buying a new one, but at over £300 I want to be pretty sure that its the cause of the problem.

    Paul
     
  2. shawxhurst

    shawxhurst Formula Junior

    Nov 6, 2006
    672
    San Diego
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    Steve Hawxhurst
    #2 shawxhurst, Mar 25, 2011
    Dave Helms over here in Colorado managed to sand/file out a crack on one of mine. But if you can't see a crack or signs of tracking then...........
    Sounds like you've eliminated ignition wire, extender or plug as the cause by your substitution.
    The only good news I can think of is that the caps are available over here for less than 200 quid. Won't make your eyes bleed but you'll have a nose bleed for about a week or so.

    Good Luck & Best Wishes!
     
  3. mwr4440

    mwr4440 Five Time F1 World Champ
    Rossa Subscribed

    Jun 8, 2007
    55,933
    Bavaria, The 'Other' Germany
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    Mark W.R.
    #3 mwr4440, Mar 25, 2011

    Paul,

    Are you sure the injector is working properly? Is that cylinder getting the correct amount of gas?
     
  4. Fave

    Fave F1 Rookie

    Aug 12, 2010
    4,157
    Tarana
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    L. Ike Hunt
    #4 Fave, Mar 25, 2011
    I have a used cap lying around if you want. Pm me if interested.
     
  5. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    Mike 996
    #5 mike996, Mar 25, 2011
    If you check the cap closely under a strong light you should be able to see cracks or carbon tracking. THere is no fix for either one except for a new dist cap. Rotors can also carbon track though usually when they do, they track to ground (the dist shaft) and an engine either won't run at all or misfires badly in general.

    Note that often a bad cap/rotor/wire/plug can fire OK at idle/light load but misfire under load. ALSO - a plug that fires OK sitting out may not fire OK in the engine because the compression causes a greater electrical load on the plug to fire. Again, this could be any of the ignition issues - bad plug, bad wire/connector, bad cap, etc.
     
  6. paul 308

    paul 308 Karting

    Jan 13, 2004
    110
    Guildford, Surrey UK
    Full Name:
    Paul Deslandes
    #6 paul 308, Mar 25, 2011
    I'm pretty sure I've eliminated everything else. As its a carburettor car, an injector is not an issue. I've had all the carbs to bits and used Birdman's excellent float adjustment procedure and cleaned all the jets.

    I note the point about the plug not performing the same under high compression.

    I will take the cap off again and have another look to see if I can spot a fault.

    A new one here in the UK from Superformance is 268 pounds plus 20% tax. Fave, thanks for the offer. I'll pm you the details to see if you have the same type.
     
  7. viphoto

    viphoto Formula Junior

    Sep 11, 2010
    264
    Carlsbad, CA
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    Mark
    #7 viphoto, Mar 25, 2011
    Paul
    I just ran across a problem like yours with my car and thought for sure it was electrical...double check the idle jet for that cylinder ...My car was running fine and after a short test drive I had a misfire (I then swapped plugs, extenders and even a couple of wires) before pulling the idle jet and removing a ittty bitty something from it (barely perceptible to my eyes) and the misfire was gone. It killed that cylinder to the point that pulling the plug wire made no difference in the idle.
     
  8. mwr4440

    mwr4440 Five Time F1 World Champ
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    #8 mwr4440, Mar 25, 2011
    Last edited: Mar 25, 2011
    Guessing but very possibly a speck of rust or "varnish" (residue from dried maus piss (fuel)).

    Cleaning my fuel parts readying for DaveH's fuel hoses and the rebuilding of a fuel distributor and the amount of gunk found in those areas is unbelieveable at the least.
     
  9. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    #9 magaoidh, Mar 26, 2011
    Paul check the price at Eurospares!!!
     
  10. paul 308

    paul 308 Karting

    Jan 13, 2004
    110
    Guildford, Surrey UK
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    Paul Deslandes
    #10 paul 308, Mar 26, 2011
    well, a big thank you to all for the advice and offers.

    I thought I'd better take another look yesterday afternoon when the sun was boring straight into the garage - light doesn't get much brighter than that! Sure enough, there's a hairline crack running down from plug lead post #2, the misfiring cylinder, right to where the cap sits on the distributor body. Further investigation using a mirror, as that post is on the underside of the dizzy, revealed evidence of arcing on the aluminium (sorry about the UK spelling) body.

    So, QED - new cap needed.

    I'll definitely try Eurospares - thanks for the tip

    Paul
     
  11. mwr4440

    mwr4440 Five Time F1 World Champ
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    #11 mwr4440, Mar 26, 2011
    Last edited: Mar 26, 2011
    Glad you found the fault.

    :)
     
  12. Speed78

    Speed78 Karting

    Mar 26, 2007
    72
    Marysville, WA
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    Gary
    #12 Speed78, May 17, 2011
    I have a Crack my Cap on 78 308 GTS. Is there a cross over part number? Where is the best inexpensive place to get a set of 2?
     
  13. Fairview

    Fairview Formula 3

    Mar 16, 2009
    1,109
    Waynesboro, Virginia
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    Jeff Ward
    #13 Fairview, May 17, 2011
    Last edited: May 17, 2011
    For my 78 308, I bought 2 caps and 2 rotors from Superformance in England. The price was very competitive. Ordered on Thursday, arrived in Virginia on Monday. Plus it had really cool stamps on the parcel....
     
  14. Sledge4.2

    Sledge4.2 F1 Rookie

    Oct 19, 2007
    4,779
    Marin
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    Geno
    #14 Sledge4.2, May 18, 2011
    check AW Auto parts.
     
  15. paul 308

    paul 308 Karting

    Jan 13, 2004
    110
    Guildford, Surrey UK
    Full Name:
    Paul Deslandes
    #15 paul 308, May 18, 2011
    I got the new (single dizzy) cap from Eurospares and a new set of leads from Superformance, both on the basis of best-price. Car's running as sweet as a nut now.

    Eurospares also had a second-hand unit available but, as it didn't come with any warranty, I decided to buy new.
     
  16. Speed78

    Speed78 Karting

    Mar 26, 2007
    72
    Marysville, WA
    Full Name:
    Gary
    #16 Speed78, May 20, 2011
    Thanks, Got them from awferrari.com $195 ea rotors $50 sent out priority mail on Wed from NJ got them today in WA. Sweet. They were very accommodating.
     
  17. magaoidh

    magaoidh Karting

    May 12, 2009
    220
    #17 magaoidh, May 20, 2011
    Glad to help,I had similiar probs and bought a new rotor as well,utilising both companies!
     

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