DS Poor Running. Spark Plug failure
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Thread: DS Poor Running. Spark Plug failure

  1. #1
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    Default DS Poor Running. Spark Plug failure

    Hello,

    I started up a thread some months ago called "DS i.e. Fast Idle problem". Thanks to all who contributed to getting me back on the road

    But I never really signed off on the final outcome.

    Over a number of months I had located dozens of minor problems in the fuel/ignition system such as
    • Cracked suction hose out of fuel tank (hard to spot, easy to replace and difficult to get the fuel pressure steady again)
    • Faulty fuel pressure regulator (changed to one with a gauge on it ... very useful)
    • Faulty connections to manifold pressure sensor
    • Probable faulty earths here and there
    • Faulty adjustments on the throttle body (I never realised that the best approach is to treat it as you would a carburetor)
    • Partially blocked crankcase breather hose (Ii think was causing the occasional but extensive smoke to blow fro exhaust. I pretend it is anyway)
    • Cold start injector not shutting off and continuously pumping fuel into system (now replaced with very similar Volvo item from local wreckers)
    • Fuel injectors variously blocked or leaking (now all replaced with new, cheap, non-original items from USA but completely satisfactory as far as I can see)
    • Faulty coil ballast-resistor had been by-passed leaving the wrong type of coil (one designed for ballast resistor) in place (I am not sure this made any real difference but all the parts are now new and correctly wired)
    • Poor wiring on the 2 relays in system. Replays and wiring replaced


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    Pheww. And while each seem to make some difference, I still had a car not firing on all cylinders

    I had replaced all the plugs at the very beginning of this process with new NGK BP6HS
    But, after one week, number 4 was not firing. So I replaced this (new) plug with another new plug and all was well
    But then it started to run poorly again (number 4 and 2 seemed to be the culprits). I assumed it could not be the plugs again so decided to go through the whole system (as above)
    But problem persisted.
    So, after some months, I replaced 2 and 4 plugs and all was well

    Meaning out of 7 new plugs, 3 were faulty.

    Now I cant say absolutely that the plugs were the cause ... perhaps I knocked an unknown lose wire in the process of swapping them over
    But I am pretty sure that the misery was caused by dodgy new plugs

    The car has done over 1000 km since ... no problem

    I wonder if anyone else has had plug problems

    Regards
    Ian
    Blueduck (aka Ian Downie)
    1974 Citroen D Special with DS21i.e. engine and 5 speed gearbox
    MGB GT V8 B.... bullet--proof and great fun
    Jaguar e-type roadster ... on the way from US of A

  2. #2
    1000+ Posts gerrypro's Avatar
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    It seems improbable that the actual plug was the problem, but then who knows! Maybe the problem is the spark plug HT lead?????
    Have these been replaced? If their resistance is too high it can cause the distributor contacts in the cap to track via an alternate path. Particular if carbon dust or moisture are present! This of course will lead to intermittent misfiring. Also check your condenser and points.
    Cheers Gerry

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    Gerry,
    Before installing the 4 new plugs I had installed new spark-plug cables, distributor cap, points, condenser and rotor.
    But I did not change those brown insulating tubes that go around the plugs. They looked perfect to me
    But I will in the future
    Ian
    Blueduck (aka Ian Downie)
    1974 Citroen D Special with DS21i.e. engine and 5 speed gearbox
    MGB GT V8 B.... bullet--proof and great fun
    Jaguar e-type roadster ... on the way from US of A

  4. #4
    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by blueduck View Post
    Gerry,
    Before installing the 4 new plugs I had installed new spark-plug cables, distributor cap, points, condenser and rotor.
    But I did not change those brown insulating tubes that go around the plugs. They looked perfect to me
    But I will in the future
    Ian
    I have never had a problem with the insulator tubes as long as they looked in good nick! How good are the secondary points in the base of the Bosch IE distributor? These fire the injectors if I remember correctly!
    Cheers Gerry

  5. #5
    Tadpole
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    I`ve had issues with NGK plugs not with my DS21 though but with our Fiat 500D (a 1 cyl 500 is no joke) and our Lancia Fulvia coupe which was eventually righted by nothing more than changing the dud plug for a new item. I do believe the quality has slipped a little. Incidently I substituted the duds for another cylinder`s plug and each played up in a previously perfect cylinder. Nothing apparent either and looked excellent.

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    Gerry,
    Those trigger points looked in perfect condition to me. If my memory serves me correctly I did actually replace them with what I believe is a new set. But, at that time, the problem persisted so I put back the originals.

    Replacing the spark plugs (3 times) produced such instant improvement that it is hard to believe it could be anything else.
    The car now starts immediately, idles smoothly cold or hot. It drives well except occasionally some hesitation (missing?) under mild acceleration. Push throttle down and hesitation goes away

    But I always wonder whether the problem was elsewhere than aforementioned spark-plugs

    Regards
    And thanks so much for input
    Blueduck (aka Ian Downie)
    1974 Citroen D Special with DS21i.e. engine and 5 speed gearbox
    MGB GT V8 B.... bullet--proof and great fun
    Jaguar e-type roadster ... on the way from US of A

  7. #7
    1000+ Posts Ken W's Avatar
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    Based on my experience with Chinese manufacture, I would guess that they have moved the NGK factory to China somewhere. Hence the huge drop in quality.

    Cheers, Ken
    gerrypro and ScotFrog like this.

  8. #8
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    Measure across the plug arm and electrode with a multimeter. It should be open circuit. However, if you find a very high resistance it may mean the plug has fouled although you can't necessarily see it looking dirty. Old fuel, too much fuel or oil consumption in a 'wet' engine with weak rings could contribute to that. Sometimes, opening up the gap or going to a different heat range plug can help.

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