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Bad Digiplex Box? - Please help!

Discussion in '308/328' started by NSXER, Nov 10, 2007.

  1. NSXER

    NSXER Formula 3

    Jan 4, 2004
    1,277
    Kansas
    Rear bank comes and goes. Coils are both fine (swapped to make sure), rotors fine, electrical grounds are good...swapped Digiplexes and determined that one of them is bad or at least going out. The strange part is that when I start the car it runs very rough, rear bank is out, but when I unplug the questionable digiplex the car runs the same (rear bank out) but when I plug it back in, the rear bank starts to fire again and all is good. Sometimes though it is fine right when I start up the car, 8 out of 10 times though it is not and I have to unplug and plug it back in. I have cleaned all the contacts on the plug and bent the connector leads for better contact. Any ideas as to what is going on? I thought that digiplexes either worked or instantly stopped working. It now has me thinking about upgrading to electronic ignition. Any thoughts?

    Thanks

    Brian
     
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  3. miketuason

    miketuason F1 World Champ
    Silver Subscribed Owner

    Feb 24, 2006
    14,301
    Cerritos, CA.
    Full Name:
    Mike
    Was the digiplex for the front bank bad? Because you said when you swap it the rear bank is now bad, is this correct?
     
  4. ragtop1

    ragtop1 F1 Rookie
    Silver Subscribed

    Nov 11, 2006
    3,167
    Ontario, Canada
    Full Name:
    Larry Warren
    My gts is experiencing the same symptoms. What and where is the digiplex box?
     
  5. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,001
    Groton, MA
    Full Name:
    Verell Boaen
    ragtop1,
    The Digiplexes are in a small well behind the driver's side rear wheel. They're under a small screwed down panel under the carpet on bottom of the luggage compartment.

    NSXER
    From the general symptoms, it sounds like the failing digiplex is not always being initialized correctly. There's a well known grounding mod for the digiplexes, does your car have it? If not, search will locate a thread with pix.
    Not having this ground mod can cause some pretty erratic Digiplex behavior.

    Altho, since you mentioned checking grounding I suspect you're familiar with the mod.

    Also, am I correct in interpreting your post as saying that when you swapped the F & R digiplexes, the problem switched to the front bank?

    Suspect you've already done this also , but have you actually removed the access panel to the digiplex compartment. I've seen the rubber drain tube for the compartment get plugged up & the compartment can be half full of water. The moisture can cause some pretty strange Digiplex behavior.

    Unfortunately, I'm not aware of anyone who repairs the Digiplexes, or even where a schematic for them might be found.
     
  6. NSXER

    NSXER Formula 3

    Jan 4, 2004
    1,277
    Kansas
    The digiplex for the rear bank is causing the problems. When I switch the digiplex to the front bank, the front bank goes out.

    Brian
     
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  8. NSXER

    NSXER Formula 3

    Jan 4, 2004
    1,277
    Kansas
    Yes, it is not always being initialized correctly. I did the grounding fix sometime ago and actually redid it just to make sure. This time I added a ground wiring to each digiplex.
    I have narrowed it down to one of the digiplexes because whichever bank it is connected to goes down. No moisture was in either unit.
    Thanks for the help, I greatly appreciate it. I wish that the units could be fixed!!!!

    Brian
     
  9. luckydynes

    luckydynes F1 Rookie

    Jan 25, 2004
    3,872
    CA and OR
    Full Name:
    pit bull
    Does anyone know the technical reason they can't be fixed?

    If someone wants to send me a bad one I'll spend a little time troubleshooting it . . . are they worth fixing or are there plenty of used ones out there? What are they going for?


    Sean
     
  10. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,001
    Groton, MA
    Full Name:
    Verell Boaen
    They should be fixable, just that w/o documentation it is going to take some serious circuit tracing & reverse engineering. The design is old enough(late '70s) so that the circuitry will be mostly discrete components, not custom chips.

    Also, some (all?) of the digiplexes had a heavy conformal coating that has to be removed to get at components & the circuit board.

    I've seen used Digiplexes go on eBAY for a couple of grand, so s/b worth repairing if it can be done for less than that.
     
  11. winfieldchristopher

    Nov 7, 2007
    2
    I recently came across this site.... http://www.the-ecu-doctor.co.uk/

    I know nothing about them but they sound like they know what they are doing... my 328 just started missing so I am a bit worried now....

    Christopher
     
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  13. luckydynes

    luckydynes F1 Rookie

    Jan 25, 2004
    3,872
    CA and OR
    Full Name:
    pit bull
    A person can buy the Haltech ecu I use for around $700 and it will control the ignition curve, two dizzy's, and fuel injection should you ultimately decide to go that route.

    It'll read the stock triggers and a $150 2 channel igniter allows you to run the stock dizzy's.

    If you want to just get rid of the dizzy's, don't buy the igniter, buy a DIS 4, a crank trigger setup (which I also have and so does Nick), and your choice of coils (I like coil on plugs) and away you go.


    I ran my stock dizzy's with the Haltech setup for about 6 months before I swapped over to the DIS4 and crank trigger setup.



    I'm still open to doing a bit of reverse engineering on one . . . but is it worth doing if there's a solution like the Haltech with an igniter?

    Good luck,

    Sean
     
  14. hackrider

    hackrider Karting

    Feb 9, 2006
    153
    Albuquerque, NM USA
    Full Name:
    Dave
    Hi,
    There is a digiplex on ebay right now (not mine, I sold my pair to Mike Tuason last year) .

    Item number: 160178095728

    Dave
     
  15. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,001
    Groton, MA
    Full Name:
    Verell Boaen
    Sean,
    Which are you using the E8 or the E6X?
    Both look pretty good, altho the E8 is obviously more capable.

    Also,I'm curious why you are going to the DIS 4.
     
  16. luckydynes

    luckydynes F1 Rookie

    Jan 25, 2004
    3,872
    CA and OR
    Full Name:
    pit bull


    I'm using E6X . . . DIS4 has capacitive discharge spark and multiple spark below 3k or something like that . . helps tq. and you might need the CDI for the small cycle COP's :)

    Another way to go would be to use two 2 channel ignitors to drive the DFI coils . .. DIS 4 is useless for driving dizzy's . . . only use for direct fire.

    The thing to know or "budget" is that the ignition outputs coming out of the Htech need to be hooked to igniter . . . you can't just hook them right to the coils . . . and the quality of this ignitor can effect your spark . . . I felt a huge difference when I first put the Htech on with more advance, stock coils, and factory triggers with just the "cheap" Htech ignitor . . . went all the way to 42 degrees advance . . . didn't ping at all 'cause low compression. You could hook up two MSD 6AL's if you want the multiple spark but that's not cheap. I'm going to experiment with two DIS4's which increases net energy to the coil . . . two coils share one output of DIS4 when you run just one . .. all making sense?

    I don't think the E8 was available when I started this.

    Sean
     
  17. msouza

    msouza Formula Junior

    Mar 14, 2005
    291
    Tennessee
    Full Name:
    Milton Souza
    If anyone has a BAD ECU and would like to donate it, I am willing to do the circuit tracing & reverse engineering. Please PM for address.

    Thanks,

    Milton
     
  18. Adaptel

    Adaptel Karting

    Jul 21, 2007
    89
    Concord, NH USA
    Full Name:
    Kevin Pearson
    I am currently taking on the challenge of documenting the schematic from an 85 308 QV digiplex box (MED 805A) that sparks, but does not advance. The first real challenge is to get through all the rubbver goo that Marelli used as an attempt at weatherproofing. I noticed that at the heart of the circuit is a strange 24-pin wide std dip chip, made by RCA with markings 93709 / RCA / 327 G. I could not find references to this chip anywhere in semiconductor databases, but this appears to be an early PROM chip that is used to hold the timing advance map. Would be nice to read the data from that chip, if I am able to identify its pinout. I'll keep everyone posted when I finish documenting this cirucit. I was really surprised to find out that nobody has done this before, or at least, done it and shared the info with others.
     
  19. franzi@senet.com.au

    May 14, 2007
    35
    Adelaide, Australia
    Full Name:
    Lynton Franzi
    I imagine that few have the expertise to trace the circuit and determine the equivalent components. However, in some cases as I found with my 308QV, the problem with the unit could be the failure or intermittent operation of the power output switching transistor which is located under the sealed material on the case.

    I have located a low cost equivalent for this component which can readily be substituted. I am also interested in finding a faulty 805A if anyone has one to attempt an a circuit analysis.
    Lynton
     
  20. NSXER

    NSXER Formula 3

    Jan 4, 2004
    1,277
    Kansas
    Lynton,
    I may have one that we can test on. What do we need to do? Mine initially does not work but then comes to life.

    Brian
     
  21. bert308

    bert308 Formula 3
    Silver Subscribed

    Nov 30, 2002
    1,776
    Roermond Netherlands
    Full Name:
    Bert Kanters
    I had a bank faulting too, when wiggling the connector it came back to life. I cut of the multi-connector and put individual connectors to each wires. I keep the cut off connectors with the boxes to know were each wire goes.
     
  22. franzi@senet.com.au

    May 14, 2007
    35
    Adelaide, Australia
    Full Name:
    Lynton Franzi
    The tyranny of distance with me in Australia makes it more difficult and costly to use your unit as a test. Perhaps if I can obtain a faulty unit locally (particularly in my case a Med 805 A, it may be more practical.

    However if you wish to PM me, we can try and work out some possibilities and worst case, I can pass on the detail of the low cost component substitution that may be worth a try, that you can have done by your local auto electrician.
     
  23. parkerfe

    parkerfe F1 World Champ

    Sep 4, 2001
    12,887
    Cumming, Georgia
    Full Name:
    Franklin E. Parker
    Go with an MSD ignition with a Blaster coil...
     

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