My Volvo is no longer trying to kill me but...

Discussion in 'General Motoring' started by blurp, Oct 5, 2004.

  1. blurp

    blurp Guest

    Re-adjusted the throttle switch to <CLICK> just as the throttle opens
    and closes and this has not caused the engine to race so one
    adjustment made, one possible problem eliminated, no problems solved.

    I would like to next disassemble the throttle body to see that it is
    clean and clear of any build-up. I have occasionally found oil in the
    air filter box and once in the pipe leading to the air intake
    manifold. By 'throttle body' I mean the area underneath the round
    metal puck with 'Turbo' written on it at the terminus of the
    air-intake pipe at the top of the engine, held down by 3 bolts. I
    believe that under there I will find my throttle plate.

    Having a Turbo makes all the documentation and diagrams I can find
    just a bit inaccurate. I'm currently working with the following

    I'm also hoping this course of investigation will lead me to make
    sense out of the following observations:

    (NOTE: By HOT I mean engine stopped and sitting for 1-2 hours and by
    WARM I mean engine stopped and sitting 2-4 hours. COLD > 4 hrs.)

    Engine Weather Result
    ~~~~~~ ~~~~~~~ ~~~~~~
    Cold Cold Starts well, idles too fast
    Hot (sits 1hr) Cold Starts/runs great
    Warm (sits 2+hr) Cold Starts with difficulty

    Cold Warm Starts well, won't idle w/o throttle
    Hot (sits 1hr) Warm Starts/runs great
    Warm Warm Starts with difficulty, erratic idle

    Also, why would it be that tapping the gas pedal when idling has the
    exact opposite effect one might expect i.e. revs drop before rising
    instead of just rising? Could it be that the throttle is allowing gas
    to enter but the the air is just late by that tiny little bit leading
    to a moment of lean mixture and, therefore, hesitation?

    Also, is there anything I can check on the cold start valve?
    blurp, Oct 5, 2004
  2. blurp

    blurp Guest

    And, as always, thanks for all your advice and taking the time to read
    my long-winded posts.

    blurp, Oct 5, 2004
  3. blurp

    blurp Guest

    OOOPS... And I forgot I was starting a new thread so the car is a 1983
    240 Turbo with k-jetronic injection system and 330K km.
    blurp, Oct 5, 2004
  4. blurp

    radietz Guest

    As always with any running/starting problem on a K-jet you have to find
    someone who can test the fuel pressures. And then take the time to check
    the fuel flow from the in-tank pump.

    From what you've stated and given the mileage on the car I would suspect
    the following given that the tune up parts, valve adjustment, and hoses
    (air in this case) are are in good serviceable condition:

    The constant idle motor depends on proper wiring at the throttle switch,
    an accurate coolant temperature signal, and proper adjustment of the
    throttle plate. Back probe the three wires on the back of the idle motor
    with a test light clipped to ground. You'll find that probing one wire
    causes the idle to raise to maximum (2200-2400 rpm), the center wire
    does nothing, and the third wire causes the motor to close completely.
    If grounding the close signal wire does nothing either the throttle
    plate is open too far, the throttle switch is not working, or the motor
    itself is stuck/gummed up or otherwise not behaving correctly. The other
    two possibilities can be addressed visually. Clean the throttle housing
    and adjust the throttle plate. See if the throttle switch clicks when
    you crack the throttle. There is also a blue-white wire that terminates
    in a blue test connector along the right front fender. Clipping a test
    lead between it and ground holds the idle motor shut while the engine is
    running and allows the throttle plate to be adjusted to something like
    750-850 rpm. Ungrounding the wire should let the idle rise to 900-

    I suspect the control pressure regulator is not working. Control
    pressure is likely too high--above 3.7 bar (engine warm). This will
    cause erratic high idle because the mixture is too lean, also diminished
    performance when hot. There is also a vacuum check valve in the plumbing
    on the bottom side of the CPR that allows for enrichment on acceleration
    when cold. When malfunctioning this causes the car to fall on its face
    after one rapid acceleration, I.e. a hard run up in first gear leads to
    NO power when second gear is engaged. The engine will continue running
    however. If you pull over and stop to see why the engine fell out, raise
    the hood, verify that it's still there, slam the hood shut and get back
    in the car you will find that it operates normally. The thermal ported
    vacuum switch that control enrichment has now closed and the CPR has
    switched to warm running operation.

    Hard starts are often caused by the deteriorated hose between the pre-
    pump and the sender unit outlet pipe. Very hard starts with prolonged
    cranking can often be the result of a leaking diaphragm in the fuel
    pressure accumulator. Extra very hard prolonged cranking to start can be
    a failure of the frequency valve, which is extremely rare.

    A K-jet without leaking injector seals is impossible to find. Replace
    the seals (upper and lower) and the stands they go into. If you can find
    someone who has one, have the injectors put on a Bosch injector
    tester/cleaner. Try to get a uniform spray pattern when flushing at full
    pressure, get the injector to chatter when just barely applying enough
    pressure to get the pintle to lift.

    The was a service bulletin that used a pulse relay to energize the cold
    start valve after a period of 10 seconds of cranking. Someone may still
    have a copy that would show the part numbers and instructions for
    installing it.

    Another maintenance item that should be address is to clean the airflow
    sensor plate. Goop builds up on the top and causes weird throttle
    response issues.


    radietz, Oct 6, 2004
  5. blurp

    Mang0 Guest

    I'm having pretty much the exact same symptoms with my 87 740 turbo.
    When I start from cold weather+cold engine, it'll barely idle at first.
    Dropping it into gear makes it splutter, then stall. Tapping my foot on
    the accelerator at the point just makes it stall faster sometimes.

    Thanks for your reply Bob :)
    Mang0, Oct 6, 2004
  6. blurp

    blurp Guest

    blurp, Oct 6, 2004
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