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Duraspark Ignition Box

Discussion in 'Intermediate CJ-5/6/7/8' started by rejeep, Oct 23, 2016.

  1. Oct 23, 2016
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Rochester, NY
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    if anybody has been following my build thread or has caught some posts on this from me in the past few months, I have been having persistent and complete failures of the Duraspark II module box.

    To recap:
    AMC 360 with a Howell TBI system
    All new painless wiring harness and the ignition system copied from a 1991 Grand Wagoner
    (tried to keep systems stock for field serviceability)

    i built this jeep over the past few years and have been driving it regularly for the past 6-8 months.

    In this short time frame, I have managed to chew through 4 ignition control modules.
    first couple would leave me with the classic intermittent failure symptoms
    the last 2 units have left me stranded without warning.
    all units I have used have been aftermarket parts store variety, mostly Standard Motor Products LX-235

    I currently have 1 NOS Mopar unit that is currently in the truck.

    What gives here?
    I can't be that unlucky that I plowed through 4 units in almost as many months.
    or Im that unlucky and got a run of bad units?

    Thoughts I have had....
    box currently mounted on aluminum firewall, AMC 360... too much heat?
    Should I move ignition box to inner fender?
    What else causes the boxes to go bad? grounding?

    Im to the point where I will be mounting 2 in the engine compartment... maybe that will fix it because ill be prepared.

    any thoughts other than HEI?
     
  2. Oct 23, 2016
    Daryl

    Daryl Sponsor

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    Grounding can be very important on them. I had a 89 yj that went through 3 or 4 boxes in a year. The single biggest reason why people give up on AMC motors is the ignition systems.
     
  3. Oct 23, 2016
    zila

    zila I throw poop

    Rock Springs,...
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    I had my ignition module mounted on the firewall .. This is aftr I instlled a TBI which included an igniton too. Burned out the module. I suspected heat. So I moved it to the fender well and used a one inch heat sink and heat sink compound to mount it..
     
  4. Oct 23, 2016
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Did you eliminate the resistance wire to the coil? All the current through the coil goes to ground through the module. You need the resistance wire to limit the coil current. No resistance and the module will overheat.

    You are sure your reluctor coil in the distributor is not going intermittantly open? The reluctor coil (with magnet) is a common service part. I would also make sure the grounds are good (as Daryl suggests) and look skeptically at all the relevant plug connections. There is no case ground indicated on the wiring diagram, but there is a black center-tap (?) wire that comes from the reluctor coil at the distributor. This is a long way for the ground to travel, and through two potentially sketchy plugs. I suspect the case is grounded too... you can check it with a multimeter. If any of the connections measures anything but 100% open with the case (l10 or 100 megaohms is open), then the case is grounded.

    The male half of the reluctor plug comes with a replacement reluctor coil. A little dielectric grease in each plug will help to abate corrosion and preserve conduction. The plug on my J20 was green with corrosion and the plastic was very brittle ... replacement time. However, it still has the original (?) AMC-branded module (knock on wood) which is likely much better quality than what's available on the aftermarket today.

    If it were mine, I would not buy another Duraspark module. Instead I would replace it with a brand-name GM HEI module. Functionally they are the same circuit, and one can be substituted for the other. This is commonly called "Stalth HEI" and is described here - Junk Yard Genius.com 'Stealth HEI Page

    Caveats - be sure to follow the directions about heat sinks and coupling compound. I run the Stealth HEI with a Duraspark distributor in my formerly-Prestolite CJ-6. I used a watertight cast aluminum box from Hammond to hold my module and a chunk of finned heat sink from some old equipment mounted on the box. More heat sink can only help.

    Yes, I would move the module to the coolest spot under the hood. You have headers? On my J20, the module is about as far away from the wire path as it could possibly be, on the flat top part of the inner fender near the driver's hood hinge. There must be 6' of wire for each connection to reach the distributor.

    Also, I'm running a Standard Ignition module on the CJ-6, which is about $35 retail. You can buy a replacement HEI module for under $10, but I expect it would fail rather quickly. AC Delco is also good, and also ca $40. Avoid Standard's (or Airtex's) budget line of parts.
     
    Last edited: Oct 23, 2016
  5. Oct 23, 2016
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Couple quick thoughts...

    I need to read through your post with a cup of coffee in the AM...

    I have had realative good success with the Duraspark in my YJ and for parts availability and spares I decided to keep it "stock"

    I'm not running headers, factory manifolds and Y pipe. My firewall is heatshielded.
    I'm running an internally resisted coil (stamped no resistor required) I don't think there is any resistance in the ignition circuit. I will look into that, possibly diagram it out.

    As far as the parts end is concerned... everything in the aftermarket today is essentially a standard part, even AC Delco is reboxed standard. I've been searching eBay and websites for NOS units, I've only been able to find one and I've been saving it.
    I've been told they use universal heat sinks so they are more susceptible to temperatures.

    Going to mount another aftermarket unit in the stock location (inner fender) and see what happens. i think a redundant system is also in order till this gets sorted.
     
  6. Oct 23, 2016
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Any pics? Where did you get the material?
     
  7. Oct 24, 2016
    zila

    zila I throw poop

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    I got the heat sink material at work. I am an electrician, or was before I retired. I still have a piece left here.. I got the heat sink compound at radio shack.. This is a GM ignition module under the plastic cover


    [​IMG]
     
    Last edited: Oct 24, 2016
  8. Oct 24, 2016
    45es

    45es Active Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I had a similar problem with a GM hei system. I did as everyone here has recommended, grounds, heat sink and compound but still the problem persisted. I ultimately found a very small area on my fusible link lead to ignition switch where the insulation was compromised. It apparently would momentarily touch the frame. The link didn't blow. It appears the pulsing of the power lead would cause the ignition module to fail. I know you have a new harness but it wouldn't hurt to look.
     
  9. Oct 27, 2016
    Desert Runner

    Desert Runner Member 2024 Sponsor 2022 Sponsor

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    I am no expert so I'll just throw this out there.
    My 78 CJ came from the factory with a Ford Blue ignition module, with an induction pick up coil in the distributor. I put in an Accell Super coil with no resistor the 1st year I owned it. I have run this setup from 78 to 99, when I installed a MSD module with variable advance. The original module was put in my son's 65 CJ-5 in 2006, and is still running. I don't know how this module differs from the Duraspark II, but might be worth looking into.

    Jay
     
  10. Oct 27, 2016
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Jay, your Jeep came from the factory with a resistance wire in the coil circuit. So, even though your Accel coil has no resistor, it's running with a resistor. The original Duraspark module needs the resistor - without it, you will have melted goo running down the inner fender.

    The MSD modules are capacitor discharge (ie a different circuit) but they can be triggered by the Duraspark distributor just fine. The MSD module does not need the resistor, but I would leave it in to protect the coil.

    It's the same module as the "Duraspark II," sold to AMC by Motorcraft to work with the induction distributor. The AMC and Ford distributors differ in shape so they will fit the respective engines, but the electrical parts are identical.
     
  11. May 16, 2017
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    And I'm back at this....

    Fried another box after installing 1.35 ohm resistor. Box still mounted on firewall down low.

    Have a question on resistors for all those smarter than me.
    How do I measure the resistance across the resistor? I took a multimeter yesterday and across the resistor was 13.9 vs 12.6 volts while running.
    Do I not have enough resistor or am I probing this incorrectly? I was under the impression anything over 9.5 volts is what's death for these boxes. Do I need more resistor?
    I have a sneaky suspicion I'm doing something wrong. Resistance is in ohm and I'm looking for a different value (volts)
     
  12. May 16, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    If you want to measure the resistance of the resistor you will need to remove one of the wires then read across the resistor with the leads. If you are measuring the voltage at the resistor then put one lead (black to ground) and the other on the terminal of the resistor coming from the ignition switch for the input voltage then move the red lead (meter) to the output terminal of the resistor and read the voltage. The diff is the voltage drop. This reading needs to be taken while vehicle has been running for some time to heat things up.
     
  13. May 16, 2017
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    And we have uncovered the first mistake....

    So I'm assuming the resistor "resists" more when warmed up? So the resistor bypass is really to help with warm starts not cold?
     
  14. May 16, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    That is correct.
     
  15. May 16, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    The bypass is to make a stronger spark when starting. As soon as you release the key, the spark is provided through the resistance wire. Additionally, the Duraspark module retards the spark when starting. This is an electronic feature of the module, and has nothing to do with the resistance wire. This retarding is most useful when the engine is hot, and the reduced cranking force required when retarded is most helpful.

    I strongly doubt that the resistance of the nichrome wire changes significantly over a relevant time scale. Think of a light bulb - the cold filament has a lower resistance, but the resistance rises immediately as soon as the filament lights. This sort of time-scale is irrelevant to the ignition. Essentially instantaneous. Also, the resistance wire is used because the length of it distributes the resistance over maybe 20 or 30 inches of wire embedded in the harness. The temperature change is not significant.

    The wiring diagram shows you the resistance of the wire. It's only something like a few ohms - its purpose is to limit current, not drop voltage. The ignition switches between grounded and open, and a DC voltage measurement is not meaningful. Current limiting is needed to keep the module from overheating.

    JMO - do the "stealth HEI" conversion to one of your melted modules. Replace the Duraspark module with a quality GM HEI module. Use a Delco module if available; if not, Standard is a good brand. MSD also sells "performance" HEI modules which are probably of high quality (generally the MSD stuff is very good). https://www.summitracing.com/parts/msd-5596
     
    Last edited: May 16, 2017
  16. May 16, 2017
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Tim read his post #11. I take it he has connected a 1.35 ohm resister and that is what his question is about. And I do agree with your statements in post #15.
     
  17. May 16, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Oh I see.

    I understood from post #13 that he thought the resistance of the ballast resistor (wire or block) would change as the engine warms up, and that would make a difference. While the resistance will change with temperature, I believe the changes will be small and not affect the performance of the ballast resistor. If anything, the hot resistance is higher and the current will be less, posing less hazard to the module. But that won't matter in the grand scheme of things.

    Also, I think there's some misunderstanding about the resistor bypass. Without the current limiting resistor, the spark is somewhat hotter and this helps with starting. The module can sink this much current while cranking, but it will overheat if asked to sink that much current continually.

    This is separate from the blue-white wire on the module, which is connected to the starter switch only, and retards the spark when starting.

    This topic gets discussed a lot on the Wagoneer forums, and most agree that the Duraspark replacement modules available today are of poor quality, much lower than the OEM modules. My '82 is still running the OEM Motorcraft module after 25 years and 130K miles ... (knock on wood) ... it has a big silver and black AMC sticker with Motorcraft cast into the housing. The OEM modules seemed to be fine ... they were a big improvement over the preceeding Prestolite stuff.

    Here's a link to "stealth HEI" - Junk Yard Genius.com 'Stealth HEI Page
     
  18. May 16, 2017
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Also, it's very hard to measure such low resistances accurately with an inexpensive meter. On the lowest ohms setting, zero the meter while touching the leads together - or note the reading, and this is effectively zero. Then if you measure between 1 and 2 ohms, the resistor is good.

    Note that the GM HEI module does not need a resistor. It will run fine with the resistor in place, if you choose to leave it in the circuit.
     
  19. May 16, 2017
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I might try the stealth... but the problem solver part of my needs to get to the bottom of this...

    Going to try another resistor and see if there is any more voltage drop at the coil...
     
  20. May 16, 2017
    zila

    zila I throw poop

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    Electrician here.. E=IR. or Volts equal Amps X resistance. So a resistor that has a 1.35 ohm rating in series with the load/coil will drop voltage depending on the current in the circuit. Me I'd read the volts DC across the resistor when it is live.

    The resistance value of a resistor is constant.

    Voltage drop can be proportional to the resistor value. In series. More ohms more drop. Considering the amps stays the same.


    It is the bypass circuit that causes the full volts to apply.
     
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