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Ignition Problem, Ideas Welcome>>

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Burt4x4, Jan 26, 2002.

  1. Burt4x4

    Burt4x4 3/4 ton status

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    Specs ~ 72K5,350 w/MSD 8360Dist,Blaster2 coil,6A Box. Performer intake w/Edl1901 Q-jet on top

    OK in late Nov at Pismo Dunes my rig started to hesitate then POW backfire out the tail pipes LOUD! The enigine would completely stall then, re-light it self or fire backup. So when I got home I rebuilt the carb, reset the air to fuel while adjusting the timeing as well. I ended up with about 18 on the vacume gage and 8 deg on the timing (was down on 4). On the test drive I thought I had it solved. But the next morning POW<img src="http://coloradok5.com/forums/images/icons/mad.gif">!
    So a couple weeks whent buy and I found some time to tear into it agiain. Whent to start the rig and it would not fire up<img src="http://coloradok5.com/forums/images/icons/frown.gif">. I found the cap & rotor were toast so replaced thoes and my rig fired up again but the "STALL .......POW" is still happening.
    I emailed MSD and they said I should send in my Dist and they can test/repair it for no more than 75 bucks max charge?
    I'm kinda out of ideas, this morning I put in my new altinator and test drove to going down the hwy and it did it again the Tach drops to 0 when the stall hits the motor and then POW loud especially at 8am in the neighbor hood <img src="http://coloradok5.com/forums/images/icons/smile.gif">, it seams to happen when accelorating. It's got me worrid that one day it ain't gonna POW and the stall will turn into STALLED OUT....
    ANyway I'm gonna go drink a beer....
    Thanks


    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  2. wrath

    wrath 1/2 ton status

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    I'm no expert at this kinda stuff,Burt.but I'm gonna take a stab at it,anyway..sounds like you've checked most of what could be wrong out already..Backfire is normally a timing or carb problem as far as I know so I'd check to make sure your not firing 180 off on the dist.or possibly jumped your timing chain.Also when you rebuilt the carb did you happen to check out the powervalve..I dont know alot about carbs but know a bad powervalve will cause backfire but I think that causes a pop thru carb not exhaust..normally a timing prob causes backfire thru exhaust..hope I've somehow helped and good luck..

    70K5 350ci.350/205 "PROJECT 40"BOGGERS" It runs and its clean !!
    <a target="_blank" href=http://communities.msn.com/OurMudToys/the70k5blazer.msnw>http://communities.msn.com/OurMudToys/the70k5blazer.msnw</a>
     
  3. 71RestoRod

    71RestoRod 1/2 ton status

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    Sounds to me like a loose connection... like turning the ignition off and on again while you're going down the road... BOOM. I'd hook up the voltage meter and start shaking wires. Could be a short in the coil wire too, but if you've got the MSD in there, that wiring is probably good. How's your ignition switch?
     
  4. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I'll take an educated guess that you're on the right track with something being wrong with the distrubuitor...
    You said the tach drops to zero when it stalls or goes [POW]...
    The tach is hooked up to the negative side of the coil which sends a digital signal (on/off/on/off), if you were to check with a test light on the neg. side of the coil it would blink on and off, which tells you the dist. pickup is good and working...
    So if you lose that tach signal at the same time the stall happens I'd think it would be that you are losing spark from your distribuitor. Like the module or the pickup is intermitantly "taking a dump" or failing to work. I'd be afraid it'll eventually go out completely too.

    Sounds like you're on the right track. It sucks to fork over 75 bones though!

    [Real Men Don't Care About Gas Mileage Or Rapid Tire Wear!]
    1972 K/5
    Ryan B.
     
  5. Burt4x4

    Burt4x4 3/4 ton status

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    Thanks Guys, wierd thing is yeaterday I fired up my rig and let it get nice and warm then took the kids to grandmas house. It only did it once but every now and then I can feel the motor skip a beat. Not a whole lot but I can feel it, just barly.
    anyway...... Thanks again

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  6. skyblazer

    skyblazer 1/2 ton status

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    Burt, I would guess it would be your 6A box (or the wiring to it). Since you are losing tach signal at the same time as the miss, I would suspect that the box wiring has a bad connection or a bad ground. I'm assuming that you have your tach signaled by the tach output on your MSD box. Good luck with the troubleshooting!
     
  7. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Burt,

    Maybe a broken wire, or a wire that's through the firewall with no grommet? Vibration could've worked something loose, or maybe chaffed a wire and shorted it out. You could always run a "bypass" wire around the suspected wire (disconnecting the original of course) and see if the problem goes away.

    Sorry for the "simplistic" troubleshooting techniques, but that's all I've got for ya!!!

    I'm doing a LOT of electrical "cleanup" work in my engine compartment and can't believe the amount of corrosion on connectors that are there. Gotta get them cleaned up and slathered in a thick coat of dielectric grease!!!



    -Greg72

    '72 K5 Blazer - 427BB/TH350/NP205/6" Lift/35x12.50's
    <font color=blue>See it here: </font color=blue><a target="_blank" href=http://coloradok5.com/gallery/albun38>http://coloradok5.com/gallery/albun38</a>
     
  8. Burt4x4

    Burt4x4 3/4 ton status

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    I'm thinking that two fellas! I can rewire everything even bypass the 6Abox cuz my 8360 can run with out it.
    The only 'stock' wire in the mix is the switched + that the key truns on, so I will rig that up differnt too and see if my symptom goes away.
    I know the sparkplugs are not getting juice when the stall happens cuz thoes cylinders fill up with air/fuel then the spark come back and BOOOOM, I mean loud, VERY loud[​IMG].
    Thanks guys

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  9. bouncytruck

    bouncytruck 1/2 ton status

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    I had a similar problem in my '69. When it got warm it would sputter, sometimes back-fire and die. I rebuilt the carb, replaced the plugs, wires, cap, rotor, control module and finally the whole distributor but I still had the problem. I checked out the ignition switch and the plug into the back was melted and the switch was bad. When it got warm, the melted plug would expand and the loose connection. I replace the plug and the switch and it works great now.


    '69 K-5/350/TH350/35's & 6" Lift
     
  10. Steve_Chin

    Steve_Chin 1/2 ton status

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    Bypass the MSD box first and see if the problem goes away. My buddy with the red Blazer had some wierd ignition problems and sent his distributor and 6T box back to Autotronic for diagnosis and they replaced the pickup and reluctor in his distributor and some capacitors in the 6T box.

    Also, it concerns me that your rotor was fried. How old was it? What's your plug gap like? Have you taken a VOM to the wires to ensure good continuity?
     
  11. Chaz88K5

    Chaz88K5 1/2 ton status

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    hey burt i am afraid to tell ya i think its a lost cause....what ya should do is just park it and let me come pick it up and get it ouf of your hair...then ya dont have to worry about fixin it again...lol i figured i would try at least [​IMG]

    <font color=green>Chaz</font color=green>

    [​IMG]<a target="_blank" href=http://community.webshots.com/user/chaz88k5>http://community.webshots.com/user/chaz88k5</a>[​IMG]
     
  12. Burt4x4

    Burt4x4 3/4 ton status

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    ahhh Chaz...........NO![​IMG][​IMG]
    Dr. Chin ~ Quack Quack, how was your season? Mine was a heck ov alot better than last year!! Got my first Canadian[​IMG] and my first male Pintail or Sprig whatever you wana call it!!
    Anyway the cap and rotor really weren't all that old. The cap's inside contact was sunk in so I think if that was like that from the begining(unnoticed factory defect) then it would have been arcing to the rotor from the getgo???? I also was thinking when I was in Pismo for a week and it rained like cats and dogs + the salt air/moister= corrosion? I did replace the coil too with this new set of cap&amp;rotor. I'm gonna bypass the key switch and go right to a toggle switch to make sure it's not the + on the coil that is dropping, if it still does it then I will bypass the 6A box, then if it still does it i'll yank out the dist. and send it into MSD......
    How does that sound oh and my plug gap is 45 fairly new wires and plugs (last summer) so.......


    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  13. Steve_Chin

    Steve_Chin 1/2 ton status

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    I didn't go out at all this season, Steve. Couldn't afford it due to the lack of employment. Got a Canada, eh? Cool. The day I shot my first Canada, I got two of 'em in the fog. They were tasty. Sprig are even tastier.

    Sounds like you have a good plan on diagnosing the system.
     
  14. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Burt,

    Any updates on this issue? It's got my curiousity going now.....



    -Greg72

    '72 K5 Blazer - 427BB/TH350/NP205/6" Lift/35x12.50's
    <font color=blue>See it here: </font color=blue><a target="_blank" href=http://coloradok5.com/gallery/albun38>http://coloradok5.com/gallery/albun38</a>
     
  15. Burt4x4

    Burt4x4 3/4 ton status

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    Well not really, I did hook my meter to the + wire that the key truns on and then started wiggling everything, including the key switch. BUt couldn't get the 12.5V on the meter to drop or blink out.
    I am gonna bypass the 6A next and will let you know......

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  16. FRIZZLEFRY

    FRIZZLEFRY 1/2 ton status

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    Could it be that wire that we repaired at Blazerfest?

    Some people shouldnt drive anything bigger than their head.<a target="_blank" href=http://community.webshots.com/user/beaterwhang>community.webshots.com/user/beaterwhang</a>
     
  17. Burt4x4

    Burt4x4 3/4 ton status

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    naa, that was a bad crimp on the conector to the battery, I did recheck that thou...
    I drove my K5 to work today and it doesn't have any issues cruzin down the hwy!!
    At lunch I took my bud out for a ride to show him the symptom and he thinks it the 6A box cuz the tach drops to 0 when the stall hits. The tach connect to the 6A box and the box then connects to the coil. SO this wheekend I will rewire with out the 6A and go from there.....
    )(#$(#@#$!)#@(#@$(!@#$#)%*#!_)($**(#&amp;!@)([​IMG]

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  18. Klef72K5

    Klef72K5 1/2 ton status

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    Burt,
    I agree with Skyblazer and Steve.
    I also have a 79 cj7 that has the MSD off road ignition box. When I first built it and got it on the road the damn thing kept dying on me. It back fired a couple of times, sometimes it would start right back up and other times it wanted to sit for awhile and leave me without a Bud. Anyways I had the Mallory Unilite distributor and it would run without a ignition box, so I wired it without the MSD too see if it would die on me. Well long story short....it never died so I sent back the MSD and they replaced it for free.
    If I were you and your distributor will let you run without a ignition box I would try it. Hell I even left the wires there that way I had a back-up ignition system and it only took one wrench and 3minutes tops! It's a lot cheaper than $75

    <a target="_blank" href=http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg>http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg</a>
     
  19. 72gmc-burb

    72gmc-burb Registered Member

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    I had a very similar problem, and after swapping lots of parts, found out that I had a bad condenser. It would short out under certain vibration conditions, cause backfire, and create general havoc.

    Hubcap
     

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