89 760 Turbo engine shutting down!

Discussion in 'Volvo 760' started by george, May 8, 2007.

  1. george

    george Guest

    My 760 Turbo will be running along fine, then suddenly the engine just
    stops! In a few moments, it will start again and run for weeks
    without problems. Could it be the fuel line, or perhaps an electrical
    problem?
    Many thanks!
    Bass Man
     
    george, May 8, 2007
    #1
  2. george

    James Sweet Guest


    I think '89 is new enough that the engine wiring harness will be fine, but
    it's worth checking for rotting insulation, if you find some, there will be
    more in hidden places.

    When it shuts down, does the tach drop like a rock or does it drop slowly
    with the engine RPM? If you try to start it immediately afterward, does the
    tach twitch or just lay there dead? If you get tach activity then the ECU is
    getting a signal from the hall sensor, that will help narrow things down.
    Ignition power stage and fuel pump relay are both reasonably common
    failures.
     
    James Sweet, May 8, 2007
    #2
  3. It is vital to determine whether it is the ignition or fuel that is
    quitting. Look at the tach the next time it dies; if the pointer has already
    dropped like a stone even though the engine hasn't come to a stop the
    problem is in the ignition. If you missed the moment, watch the tach while
    you crank. If the tach doesn't twitch every second or so, the ignition is
    the problem. Also, usually fuel delivery problems have a softer fail, like
    the power sags away in a second or so, while ignition failures are typically
    abrupt as though you turned the ignition off.

    There are a few causes of each problem area - fuel or ignition. Your
    description has me thinking it is the notoriously hard to diagnose Crank
    Angle Sensor, though. It affects the ignition (and fuel, too, but the
    ignition is obvious) and comes and goes as it pleases. Others will weigh in
    with more ideas and some troubleshooting will help narrow the search.

    One quick item: does your battery have a ring terminal fastened to the bolt
    on the positive post as my '85 does? If so, it's worth your while to clean
    the battery terminals, including scraping both sides of that terminal to
    shiny metal. When it corrodes the ignition cuts out at odd times.

    Mike
     
    Michael Pardee, May 9, 2007
    #3
  4. george

    george Guest

    Many thanks guys. I'll check out your ideas and will get back to
    you. I didn't look at the tach, but the engine cuts out instantly
    which leads me to believe it's an ignition problem. The battery
    terminals are already super cleaned. You can plow fields with a
    Volvo, but their electrical sytems are often a nightmare!
    BTW, where is the Crank Angle Sensor located? Is it something I can
    locate and replace?
    George
     
    george, May 9, 2007
    #4
  5. george

    James Sweet Guest

    It's on the bellhousing, I don't believe it's difficult to replace.
     
    James Sweet, May 9, 2007
    #5
  6. That makes it sound difficult, but it's right at the top where it's only
    aggravating rather than maddening. The truly maddening part of crank angle
    sensor failures is tracking it down. The failures are often so random and so
    short-lived it's hard to get the goods on it. Sometimes they fail suddenly
    and completely (like mine did last year), but that is the luck of the draw.

    Mike
     
    Michael Pardee, May 9, 2007
    #6
  7. george

    James Sweet Guest

    My cars don't have them, but I suspect some freeze spray might make tracking
    down the failure easier, or you could just take the gamble and replace it.
    If that wasn't the problem, at least you then have a spare which you'll be
    glad you have should it ever fail.

    I'm curious if it's a hall or VR sensor, the VR type is just a coil of wire
    on a magnet and rarely fails, perhaps engine compartment heat is hard on
    them though.
     
    James Sweet, May 9, 2007
    #7
  8. Mine is almost certainly a Hall sensor. It has three leads: power, ground
    and output. I can see the output with a voltmeter. In my '85 it is mounted
    in the distributor, so I can hold the assembly in my hand to test it. After
    replacing the sensor I could also turn the distributor shaft and see the
    spark.

    When I worked in component level electronics I learned to dread intermittent
    coils. They were rare enough, but they failed just like the crank angle
    sensors do: open when they want to be, working when they feel like it, and
    no temperature sensitivity. It always came down to luck to catch them in the
    act.

    Mike
     
    Michael Pardee, May 9, 2007
    #8
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.