505 STIsluggish performance when cold
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  1. #1
    Tadpole
    Join Date
    Jul 2004
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    GEELONG
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    26

    Default 505 STIsluggish performance when cold

    Hey guys
    The car starts and idles when cold but when u accelerate the thing is flat as a pankcake till maybe the temp guage goes to 1 and a half bars from the bottom line then at about 2.5 grand it then clears and runs well. Only does it when cold so i assume its the cold start circuit
    Any hints or help here would be appreciated
    Hope u all had a wonderful xmas
    Nick

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  2. #2
    Fellow Frogger!
    Join Date
    Feb 2002
    Location
    Tamworth NSW
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    496

    Icon7

    The possibilities here are many.

    You may have a leaking / cracked vacuum / breather hose. The air flow sensor for the fuel distributor may be sticking or out of calibration.

    The additional air device may be faulty, resulting in a very lean mixture during the warm up period.

    The warm up regulator, which controls the fuel pressure regulator, may be faulty, which again is causing a lean mixture during the warm up stage.

    However, I am assuming that the mixture is not over-rich during warm-up. This may be due to the cold start injector circuit not cutting out after the appropriate number of seconds (based upon engine temperature).

    Finally, do not overlook some more basic causes. For example, incorrect spark plugs (heat range not correct), faulty ignition leads, cracked or contaminated rotor cap etc. What is the condition of the injectors?

    I have also seen the same / similar problem caused by low grade fuel. A change to a premium grade within a tank or so vastly improved the cold starting / acceleration characteristics. This is a long shot, based upon your description.

    Cheers,
    Kim.

  3. #3
    Tadpole
    Join Date
    Jul 2004
    Location
    GEELONG
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    26

    Default which hose is it

    Thanks kim for the suggestions, which hose do you refer to?
    i use hi octane pulp but i notice that this problem is getting worse
    i will renew the leads, dizzy, rotor etc. spark plugs r new bought from eai
    thanks
    nick

  4. #4
    Fellow Frogger!
    Join Date
    Feb 2002
    Location
    Tamworth NSW
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    Icon7

    Hi Nick,
    The success of a correct fuel/air ratio with the 'K' Jetronic system relies upon a predetermined vacuum and air flow to the air flow sensor. That is, relative to the throttle plate position.

    For instance, if you look at the hose connections on top of the valve cover, you will see that one goes directly to the underside of the plenum chamber. The plenum chamber is connected directly to the four induction tubes, so has a constant vacuum applied to it.

    This vacuum is also connected via other smaller hoses to, for example, the fuel pressure regulator (drivers side front of cylinder head above the water pump); also, the additional air valve (the front of the cam belt cover, near to the thermostat).

    Below the plenum chamber (in the middle of the induction tubes) is the secondary idle speed adjustment. You will note three major hoses coming of this adjuster, any one of which, if cracked, loose etc will interfere with the balance of vacuum and air flow.

    I am only touching on the possibilities. Another can be a faulty main fuel pump (behind the fuel tank), which is down on total pressure, thus having insufficient fuel flow for the richer mixtures required when cold.

    I recently had a problem with too rich a mixture when hot with our '84 505 Executive. The problem was one of the short (2 cm) hoses connected between the injector nozzle housing and the vacuum rail that lies parallel to the cylinder head had split. I replaced all four hoses, plus the nozzle and housing 'O' rings, which made a world of difference.

    What about the distributor vacuum advance capsule? Also, the initial advance setting (8 degrees BTDC)? I hope that in trying to be helpful, I am not over complicating the possibilities.

    Cheers,
    Kim.

  5. #5
    1000+ Posts Wildebeest's Avatar
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    Oct 2004
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    Perth Western Australia
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    Default 505 sluggish when cold

    Quote Originally Posted by KIMDEB
    The possibilities here are many.

    You may have a leaking / cracked vacuum / breather hose. The air flow sensor for the fuel distributor may be sticking or out of calibration.

    The additional air device may be faulty, resulting in a very lean mixture during the warm up period.

    The warm up regulator, which controls the fuel pressure regulator, may be faulty, which again is causing a lean mixture during the warm up stage.

    However, I am assuming that the mixture is not over-rich during warm-up. This may be due to the cold start injector circuit not cutting out after the appropriate number of seconds (based upon engine temperature).

    Finally, do not overlook some more basic causes. For example, incorrect spark plugs (heat range not correct), faulty ignition leads, cracked or contaminated rotor cap etc. What is the condition of the injectors?

    I have also seen the same / similar problem caused by low grade fuel. A change to a premium grade within a tank or so vastly improved the cold starting / acceleration characteristics. This is a long shot, based upon your description.

    Cheers,
    Kim.
    Duderduderini.
    I would bet your money on Kimdeb's paragraph 3. The warm up regulator or in Bosch speak, the control pressure regulator is faulty.
    Back in my dark days we could sometimes cure this by gently, with a punch, tap on the small,5mm plug on top of the regulator. Don't over do it,about half a mm for starters. This can meet your problem half way by slightly richening the mixture when cold but also ditto when warm. It should improve the 505's driveability when cold.

    This trick is only meant as a standby until you can get hold of a recon. unit.

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