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repair aotomotive ignition control module?

Discussion in 'Electronic Repair' started by William R. Watt, Jan 21, 2004.

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  1. Has anyone repaired the ignition control module off a car?
    I'm in the process of looking for someone locally who might take a look at
    one. I 'll append a description below.


    Wondering if anyone would look at a small electronic device and
    tell me if it can be diagnosed and repaired. The device is an
    electronic ignition control module off a 1989 Ford Festiva. The
    device sits inside the distributor and regulates when the spark
    plugs fire. It gets a pulse from a pointer passing a magnet on the
    rotating distributor shaft and opens a circuit to induce a small
    current at high voltage to fire the spark plugs. From a discussion
    in the newsgroup it seems its usually the
    transistor used to open the circuit that fails on ignition control
    modules. I've had to replace the one on my car twice since I
    bought it in 1989.

    I took one of the old ones apart. It's a small circuit board on a
    metal base plate glued to a black plastic cover into which are
    moulded the contacts for the wires on the distributor.

    I've read up on early ignition control modules in automotive
    electronics books from the public library. I made photo copies of
    typical circuit diagrams. They may be irrelvant if all it needs is
    to test the components on the circuit board and replace any bad
    ones. According to the books there is a diode, some resistors, and
    3-4 transistors in the basic circuit. There is also a wire from
    the car computer to advance the timing under certain conditions.
    That circuit might go through a signal converter which could be
    the big square thing on the board.

    It would be nice if this could be repaired. I understand
    transitors don't cost much. I would like to post any information
    on the Internet for other Festiva owners because they all have to
    replace these modules. There is a website and a Yahoo group
    devoted to Festivas.

    There is an auto parts store on Merivale Road at Clyde which tests
    ignition control modules for free. That's how I was able to trace
    the problem with the car engine to the ignition control module. I
    can also take a repaired module to the store for testing. I have
    the printout from the earlier tests. It might help dignose the
    failed module if needed.
  2. James Sweet

    James Sweet Guest

    If the module isn't potted in epoxy then repairing it shouldn't be too hard,
    the transistor is likely house numbered though if it has any markings at
    all, so some guesswork will be needed to find a suitable substitute.
  3. Jim Yanik

    Jim Yanik Guest

    Transistors used in the flyback section of TVs would be a good choice for a
    But device packaging may be different.
  4. Dave Cole

    Dave Cole Guest

    I promise you it isnt worth it. My day job is as a diagnostic tech, and
    I repair any circuits I can, but these are only useful for educational use.
    Twice in 14 years isn't too bad; these have to handle 300 volt or higher
    pulses, high dV/dT spikes, high/low temperatures and thermal cycling, etc.
    These are usually thick-film hybrid assemblies on a ceramic substrate,
    with active devices direct bonded and wire bonded (ie welded) connections,
    and a silicone jell sealant/thermal equalizer over all. The power
    transistor usually dies. Try buying just one bare chip power tranny, and
    then try bonding and wire bonding it: I think youll prefer the small price
    of a new one, instead. Some aftermarket units do use off-the-shelf
    components, but still aren't worth the effort.

    Good Luck
    Dave Cole
  5. thank your for the information.
    new modules cost $147 - $291 locally, transistors about $3.
    the economcis look good and other owners report the same problems on the
    Internet. I'd like to see if they can be reaired.

    the wide range in prices at local auto parts sellers is interesting
    because they are all selling exaclty the same module made by Mitsubishi
    in Japan. :)
  6. R.Enns

    R.Enns Guest


    I'd suggest going to the local auto wrecker, and buying up a half
    dozen for spares. Surely they wouldn't charge you more than $10
    apiece? The other option is to find another vehicle with similar
    ignition system, and find an alternate that is more readily available.
    GM HEI ignition parts are dirt cheap, but I believe they are designed
    to work with inductive triggers.

  7. that would be great but I called all the wreckers in the yellow pages and
    only found one with an '89 Ford Festiva. the module was used on the '88's
    and '89s but they didn't start selling Festivas in Canada until '89. in
    '90 they changed the ignigion system. I paid $75 + tax for the
    distrubuteur off it and the module failed the test. (
    sells testers to auto parts stores.) :(

    .... The other option is to find another vehicle with similar
    good idea. have to think about how to do that.

    I think some of the HEI systems used Hall Effect pickups and some used
    magnets. the Festiva uses a magnetic (inductive?) pickup. I have some
    diagrams of GM HEI circuits from an automotive electronics book at the
    public library.

    I just started looking through "Troubleshooting Analog Circuits" (1991) by
    Robt. A Pease from the library today to see what's involved. The technical
    stuff is all Greek to me but war stories are interesting.
  8. R.Enns

    R.Enns Guest

    that would be great but I called all the wreckers in the yellow pages and
    Wow, didn't realize they were that uncommon. There are some big u-pic
    yards in the Toronto area that might be worth a look. Dominion in
    Hamilton/Stoney Creek, and Standard in Markham come to mind.
    If you have a magnet rotating in your distributor, then I'd imagine
    it's a triggering a hall effect transistor in your module. Inductive
    pickups simply pass ferrous metal in front of a fixed magnetic field
    created by the stationary sensor. In any case, there must be a way
    you can modify your existing hardware to work.

    Years ago I messed with distributor-based electronic ignition systems.
    One that I found readily available, cheap and reliable was the
    Mitsubishi system used in Hyundai Excel and Dodge Colts. The pickup
    is a self-contained inductive pickup and coil drive system in a very
    small module. Two wires to the coil, and you are done. I adapted
    this system to another vehicle by simply swapping the entire system;
    pickup, reluctor (rotating toothed wheel), and coil. You should be
    able to adapt this or a similar system to your vehicle with little

    Best of luck!
  9. that's the one
    a possibility. this module is shaped to fit the base plate inside the
    distributor. it has one additional wire from the computer to advance the
    spark when the engine warms up and the oxygen sensor starts functioning.

    the ones with two more wires control the spark between cranking the engine
    and when the O2 sensor warms up. One of them would work just ignoring the
    two extra wires.

    its good to have options to try.
  10. James Sweet

    James Sweet Guest

    Perhaps you could get all the parts that changed off a '90 and swap over the
    whole system? Or scrap the car and get something better, something that
    should be possible for about what you'll spend keeping that thing going for
    a few more years.
  11. the car only has 101k km on it and should run until its well over 200k. I
    only put 2,500 km on it, summer driving only, no commuting. in very good
    shape otherwise. the electronics they put in cars is making it difficult
    for owners to do their own mainenance and repairs. every year they add on
    more. :(
  12. Guest

    Sounds like the spark curve is determined by the module, with the
    engine computer having an input to induce a fixed iming change for
    cold starts. In any case, this may present a problem trying to
    substitute another module from a different vehicle.

    You mentioned you opened the module up, are there any markings on the
    transistor you suspect? If you have a multi-meter, do you read any
    dead shorts across the legs (obviously blown transistor)?

    Post a link to a picture if you can. I'm sure someone here can make a
    suggestion for a possible replacement, but the trick is figuring out
    what type of transistor it it (mosfet, scr, pnp, npn, etc). A
    schematic of the circuit would be very helpful as well. For example
    is one leg hooked to +12v or ground and which leg is connected to the
    coil, etc.

    I applaud your efforts to learn basic electronics repair. Having some
    basic repair skills is allways handy and saves money in the long run.

  13. James Sweet

    James Sweet Guest

    That's not completely true, car electronics are generally quite reliable,
    there's some dud designs out there though. I know I'd rather tinker with a
    control module with a soldering iron than mess around with a carburetor.
  14. iliterate

    iliterate Guest

    I am looking for modules to draw. They probably will die in the
    reverse engineering process. If you want to donate one I will send you
    a copy of the finished diagram. If interested I need:
    Module,make and model of vehicle,permission to discard dead unit,YOUR
    address.It may be a while before I get the schematic ready.
    po box 1113 CASPER WYOMING 82601 USA.
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