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how do I bypass the spark control module?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by stock86, Mar 20, 2002.

  1. stock86

    stock86 Registered Member

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    Ive had a problem with my 86 k5 for a while now with it quiting or failing to crank sometimes. when it quits it will usually start back up instantly. I've found when this happens I have no fire to the plugs. Ive changed the ignition module,pick-up coil,cap rotor and plug wires in the distributor, replaced the ignition switch on the column, checked for loose or frayed wires and replaced the positive cable from the batt.
    A friend was telling me it sounded like the spark control module, at least that what I think its called. the box under the passenger side dash that has 4 wires going to the distributor.
    How can I bypass this to check and see if its the problem, also what is the purpose of this module. thanks
     
  2. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    You have to cut wires comming out the firewall and tape them together and it'll work. So you just make a loop is all. I can't remember the order for sure, but its cake.
     
  3. beefjerky

    beefjerky Registered Member

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    i have had the same problem with my 86 k5. i have replaced everything from point a to b. are the wires from the firewall coming from the spark control module or the distributor? which way are you going for the loop? will it still pass the dreaded emissions test and run correctly?
    thanks
     
  4. ChevBlazin

    ChevBlazin 1/2 ton status

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    Get an HEI distributor made to work with out the spark controm module. Thats what I did. I think it's made for an 84? Camaro. If I recall I got it at NAPA, they directed me to what I would need.
     
  5. stock86

    stock86 Registered Member

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    I hate to buy a dist. just to check the module. maybe someone can tell me what colors to splice togeather. btw we dont have emission testion in Mississippi so that is not a concern. I just want to bypass for trouble shooting. if it turns out to be the module I will replace the dist. to one without the module wires. thanks again
     
  6. rlhenry

    rlhenry Registered Member

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    If I remember correctly, I changed the pick-up coil and ignition module to those from an '80 Blazer. Now I have the 4 pin module instead of the 5. It's probably not emissions legal, but in rural AZ it doesn't matter.
     
  7. stock86

    stock86 Registered Member

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    o.k. let me see if I have this right. if I change to a 4 pin ignition module I can just leave the spark control module wires unhooked?
     
  8. TopOff

    TopOff 1/2 ton status

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    Is this fuel-injected?

    Why not ask the computer what's wrong?

    Jumper the ALDL and count the code coming from the "Check engine" light.
     
  9. DesertDueler

    DesertDueler 1/2 ton status

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    He is talking about the computer controled carb. I have one in my 86 as well.
     
  10. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    No he's talking about the ESC module. It was used from 81 to 86. I unplugged mine and swapped in an early HEI distributor...I had some drivabilty issues until i swapped distributors. I just left the ESC unplugged...

    Rene
     
  11. Blue85

    Blue85 Troll Premium Member

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    This is a common misconception. GM trucks were not computer controlled until TBI came in 1987. The cars had the E4ME electronic Quadrajets, but trucks did not. The "computer" that exists in these 86 and earlier (not sure how many years back) models was the ESC. It does not affect the carb, just spark timing.

    And if it did control the engine, how would it do it with only 4 wires? Every engine with electronic controls uses at least 5 sensors (coolant temp, air flow or pressure, knock, exhaust oxygen, intake air temp, throttle position, etc.) and has several outputs (injector pulse(s), spark timing, idle air control, etc.). If your carb is electronic, it has to have wires for the throttle position sensor and mixture control solenoid at minimum.
     
  12. SVBlazer

    SVBlazer 1/2 ton status

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    Give me a second to check My rig...I did the same thing. I just unpluged the 4 wire connector and crossed 2 of the 4 wires coming from the distro together...just a sec.
     
  13. SVBlazer

    SVBlazer 1/2 ton status

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    OK...here's the deal. The 4 wire connector coming from the distro is labeled A B C D. Run a jumper between A to C and unplug the connector from the module. BTW- I understand that the module actually is retards timing if the knock sensor senses a knock....that's all.

    Hope this helps!
     
  14. greg83k5

    greg83k5 1/2 ton status

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    it is a knock sensor, no?

    ignition retard/advance depending on input from sensor-

    the engine in mine is a 77, however i'm running the newer ESC equipped distributor. i think i have my '79 somewhere, this is interesting. i wonder if the sensor was simply unplugged the unit wouldn't function....

    i would think i'd want it to function however, if it could advance timing until it sensed knock and back off......

    thoughts????

    greg
     
  15. POWERMAD

    POWERMAD 1/2 ton status

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    <a target="_blank" href=http://www.73-87.com/garage/escrepl.htm>going to a non ESC system</a>
     
  16. rlhenry

    rlhenry Registered Member

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    That's what I did and I haven't had any problems since. You do, however, have to change the pick-up because I believe the harness from the stock pick-up is for the 3-pin side of the stock ignition module. Like I said, it's been a few years since I made the swap so I might be forgetting a few things. I'll take a look at it this weekend and verify. For me, I'd rather have the 4 pin set up instead of cutting and soldering. As most of us know, when you cut, solder, splice or tape, you are exposing yourself to possible contamination, high-joints, and other potential electrical issues. If you do it right, you probably don't have anything to worry about, but I like a clean set up without splices and joints if possible. Based on the responses, the cheapest fix seems to be cutting and soldering wires from the harness together. The pick-up/module change is around $50 and your labor. The new HEI distributor is the most expensive. The best thing for you is probably to cut the wires, leaving yourself plenty of room to make up connections, then make the connections as suggested in the other posts. Run the Blazer for a while and see if that clears things up. If so, you've identified you problem and you can go about making the changes the way you want.

    It's good to know that this mod won't affect emissions. Not that my set-up is emissions legal, it's just good to know.
     
  17. stock86

    stock86 Registered Member

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    thanks POWERMAD, and SVBLAZER
    thats exactly what I've been looking for. I know what I will be doing this weekend. I love my blazer and I miss driving it. I have 2001 gmc siera that seems to just sit in the driveway most of the time. as long as my blazer is running good, I just always seem to head to the blazer for my trip to work. thanks guys,.
     
  18. emoo99

    emoo99 1/2 ton status

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    this is an old post but i recently went from my computer controlled carb on my 86 to a non-computer carter afb and a performer intake.. also swapped distributors the vaccum controlled hei.. my truck still runs like crap, diesels really bad and has NO power at all i just have to ease on the gas slow or it will die on me and if i'm already going 30 or so and try to romp on it the engine will rev up but i won't go anywhere, advanced and retarded the timing(didn't work) and checked the vaccum lines as far as i've seen there fine... my buddy said it could be the camshaft lobes wearing out but it was perfetly fine before this whole carb/manifold swap so i'm not going to drop another 7 or 8 hundred bucks to change the cam and lifters if it's just some wires i need to fix.. it dieseled before so i'm going to try the water/tranny fluid in the carb trick to clean out the carbon then give it a tune up.. but can anyone help me out with possible solutions?
     
  19. k-5 jimmy fan

    k-5 jimmy fan Registered Member

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    [ QUOTE ]
    this is an old post but i recently went from my computer controlled carb on my 86 to a non-computer carter afb and a performer intake.. also swapped distributors the vaccum controlled hei.. my truck still runs like crap, diesels really bad and has NO power at all i just have to ease on the gas slow or it will die on me and if i'm already going 30 or so and try to romp on it the engine will rev up but i won't go anywhere, advanced and retarded the timing(didn't work) and checked the vaccum lines as far as i've seen there fine... my buddy said it could be the camshaft lobes wearing out but it was perfetly fine before this whole carb/manifold swap so i'm not going to drop another 7 or 8 hundred bucks to change the cam and lifters if it's just some wires i need to fix.. it dieseled before so i'm going to try the water/tranny fluid in the carb trick to clean out the carbon then give it a tune up.. but can anyone help me out with possible solutions?

    [/ QUOTE ]

    I have a 85 Jimmy with the feedback Rochester carb, and it is a pain in the butt. I follow the instructions closely for setting the timing. Shut off engine, disconect the cpu to disributor then set, it then idles great at normal rpm. But when I shut down and reconnect cpu to disributor, the RPM increases to about 1500 on start up.

    I have been considering making a similar change as to what you did, but now I am not so sure? So will be interested in what others may have to say on the subject?
     

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