catalytic converter, AMM or something else?

Discussion in 'General Motoring' started by MW, Jun 26, 2003.

  1. MW

    MW Guest

    1998 740 turbo w/185K miles. Need a little diagnostic help. This
    problem came on very quickly. I can't be sure but somehow I think it
    is related to possibly a tank of bad gas. Then again, it may have
    been developing for a long time and may simply be age. Owned car
    since new. Changed oil and filter every 4K.

    Car always starts, stalls a few times then is OK. (in winter it
    doesn't stall) Lately, very very rough idle as opposed to normal
    rough idle. Also stalls and stumbles at idle. Never a problem
    re-starting. Lately, no or very little power below 3,000 then most of
    the power returns till 4,500 or so, then peaks. Also hear a slight
    backfire/stumble when at idle and I blip the throttle. Gas mileage is
    worst ever.

    Added techron several tanks ago. Didn't really help. Tried again,
    still no real help.

    Had annoying little oil leak (one of many over the years)which I
    traced to either the valve cover gasket or cam shaft seal. Replaced
    gasket and now get lots more oil dripping onto water pump and being
    blown everywhere by the fan.

    Pulled intake hose off turbo and found very slight lateral movement
    with almost no axial movement. I could spin turbo with my fingers.
    Expected little or no friction and it to just continue spinning, but
    it didn't.

    Checked fuel injectors, ballast resistor pack, temp sensor, knock
    sensor, air valve, throttle switch, AMM. All tested good per Volvo
    service manual. Plugs (platinum) all were uniform in light color. No
    signs of oil. Replaced dist. cap, tested wires, replaced air filter.
    checked hoses for air leaks.

    At this point in time I suspect either the catalytic converter
    (original) or the AMM. I doubt I can get the bolt out of the header
    pipe (also original)to test the pressure and I hate like hell to start
    replacing parts considering the 185K miles.

    One other observation. Over the past several months I did notice that
    under heavy accelleration the boost gauge readings were kind of
    sluggish. Any thoughts?
     
    MW, Jun 26, 2003
    #1
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  2. MW

    G Klein Guest

    Do you mean 1989 740T from what you are describing it
    possibly could be a bad turbo check for any engine
    codes in A2 & A6 post back with what codes if any come
    up
     
    G Klein, Jun 26, 2003
    #2
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  3. MW

    Brick_0 Guest

    What is your vacuum when you first start the car and what happens to it over
    the next few minutes. Normal running vacuum is 16-22. What you describe
    sounds like some major vacuum leaks. Is the engine behavior different
    between a cold engine and a hot running engine.
    I would suspect the seal behind the timing gear on the front of the cam.
    There are also seals behing the intermediate shaft and the crank.
    A turbo that's starting to go bad or a partially blocked cat can cause this.
    Has the fuel filter been changed lately? Is the behavior different if the
    tank is low on fuel?
     
    Brick_0, Jun 27, 2003
    #3
  4. MW

    MW Guest

    OOPS, SHOULD READ 1988 740 TURBO
     
    MW, Jun 27, 2003
    #4
  5. MW

    Brick_0 Guest

    It doesn't happen very often but your timing belt could have jumped a notch.



    Also hear a slight
     
    Brick_0, Jun 27, 2003
    #5
  6. MW

    MW Guest

    TIME. DON'T NOTICE ANY CHANGE IN PERFORMANCE RELATED TO FUEL TANK
    LEVEL. THOUGHT IT MIGHT BE PRESSURE REGULATOR BUT THAT SEEMS TO CHECK
    OUT. AS FOR VACUUM LEAKS, REMOVED EACH LINE AND PLUGGED FITTING IN
    MANIFOLD, NO CHANGE. USED WD-40 ON ALL VACUUM CONNECTION, ON INJECTOR
    SEALS, THROTTLE VALVE SEALS AND INTAKE MANIFOLD, NO LEAKS FOUND.

    DID THINK ABOUT TIMING BELT JUMPING A COG THOUGH. CHECKED IGNITION
    TIMING AND IT WAS AT 10 BTDC THOUGH I GUESS I SHOULD CHECK THE BELT
    ANYWAY.

    COMMON SENSE SAYS I SHOULD GET RID OF THE CAR, ECONOMIC SENSE SAYS I
    SHOULD GET RID OF THE CAR, MECHANICAL SENSE SAYS I SHOULD GET RID OF
    THE CAR, BUT THE WIFE WANTS IT SINCE SHE HAD IT SINCE NEW.

    MY CURRENT THOUGHTS ARE A COMBINATION OF PROBLEMS. AS I MENTIONED, THE
    TURBO SPUN BUT I WOULD HAVE THOUGHT MORE FREELY. MAYBE THIS IS OK AT
    IDLE BUT WHEN GIVING GAS, THE ROTATIONAL FRICTION IMPEEDS THE FLOW OF
    AIR AND IT STUMBLES UNTILL IT GAINS ENOUGH SPEED TO ALLOW FOR THE
    PROPER VOLUME OF AIR FOR COMBUSTION. THEN, POSSIBLY DUE TO A CLOGED
    OR PARTIALLY CLOGED CAT, THE SPEED/POWER MAX OUT AT THE REDUCED
    CAPACITY OF THE CAT.

    I CAN DEAL WITH THE $100+ FOR THE CAT WHICH I WILL INSTALL, BUT IF IT
    IS THE TURBO ALSO, ITS COST DOESN'T MAKE SENSE. AND WE ALL KNOW IT
    MIGHT NOT END THERE.

    MITCHEL
     
    MW, Jun 27, 2003
    #6
  7. MW

    Brick_0 Guest

    The crank and intermediate shaft (distributor) could be correct but the cam
    gear could be off by one notch. That would mean the ignition timing would be
    correct. Other than that I would strongly suspect the cat. A shop with
    computer diagnostic equipment would be able to diagnose your problem, then
    you could take if from there.

    Brick_0
     
    Brick_0, Jun 27, 2003
    #7
  8. MW

    Mike F Guest

    Look at the hoses between turbo and intake manifold. The hoses at the
    intercooler often fail on the bottom, where oil sits, and the rip is not
    readily obvious until you actually remove the hose. Even if the turbo
    completely seizes, the engine runs perfectly smoothly (well as good as a
    B230 ever is), just with little power. A plugged cat inhibits boost
    production as well, but really doesn't make the engine run poorly.
     
    Mike F, Jun 30, 2003
    #8
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