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Technical Can a Malfunctioning Tach cause Ignition issues?

Discussion in 'The Hokey Ass Message Board' started by Nailhead Jason, Sep 23, 2019.

  1. So I have just got my 39 running. I am using a stock GM points Distributor in the 283 small block. New Points NOS Mallory condenser from the 70's so its good quality. Timing is at 12 degrees advanced. Here is the issue. I can go out and crank it up to start and it will fire right off and idle perfect, Shut it off, and you might be cranking it for 20 min before it will fire again, sometimes poping out the carb, sometimes poping out the exhaust. Turn it off, then back on hit the button and it will fire right up. make no sense at all.

    I pulled the distributor and set it all back up again, put it back in and it fired right up. Having only about 1 mile of drive time on it, I took it for spin around the neighborhood. It was running but not as smooth as it should have been, and somewhat lacking in power. it was then that I noticed the Tach was acting very weird. I could rev it up, but it would never go over about 2500 RPM, and was very slow moving. So I have a Feeling this tach is not working properly. It just didn't seem to line up to what the engine was doing. Got back to the house, pulled in the drive way, shut it off, went to fire it up, and same thing......no start, pop out the carb. shut it off came back 10 min later fired right up.

    Now my question is this... The tach is a neat old AC Delco Tach, that is def old, was NOS in the box when I got it, It was marked for an 8 CYL on the rear case, and required no box to drive it. its just hooked straight up to the coil negative terminal. Is there a possibility, that this tach, is causing me issues? can it ground out the negative side of the coil and make it do weird stuff in the process? I plan on disconnecting the signal wire from the coil this evening and test it. Im at work now and just sorting of thinking out loud about it. Any thoughts, experience or input appreciated.
     
  2. Oh and all the wiring is new and tests good, i'm not losing Voltage to the coil when it wont fire, I am getting spark, but it looks weak and is very sporadic.
     
  3. das858
    Joined: Jul 28, 2010
    Posts: 651

    das858
    Member

    In the late '70's when i was a mechanic at a chevy dealer one of the first steps we would do when we had a no start , no ignition problem was to disconnect the tach . Give it a try !
     
  4. Doublepumper
    Joined: Jun 26, 2016
    Posts: 450

    Doublepumper
    Member

    Might try a different condenser. Sounds like the one in it now isn't doing it's job.
     
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  5. that was my first thought as well, I have swapped out 4 different condensers with no change.
     
  6. I've only had one car in my entire life with a tachometer and it was factory equipment on a 1963 1/2 Falcon Sprint, I was doing some repairs on the dash and I removed the tach, when I had completed my work the car would not crank.

    So from my limited experience I would say it's possible, I'll wager Jim Forbes will know for certain. HRP
     
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  7. Yes, a bad tach could cause the ignition to give troubles. It's also possible the tach is misbehaving because of an ignition problem. I once had a tach that was very erratic because of a worn out breaker plate. The engine seemed to run fine but the tach sure didn't like what was going on.
     
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  8. If the Tach reading had not been so off and slow responding, I would never have thought that it could have anything to do with it.
     
  9. Boneyard51
    Joined: Dec 10, 2017
    Posts: 2,754

    Boneyard51
    Member

    The factory Ford tach of that era had the ignition running through them! Most tachs just have a signal wire going from the coil into the tach. But both kind can cause engine runnablely problems.





    Bones
     
  10. Black_Sheep
    Joined: May 22, 2010
    Posts: 994

    Black_Sheep
    Member

    I would disconnect the tach wire from the coil and see what happens...
     
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  11. Disconnected the tach wire from the coil tonight with no change. Couldn't get it to fire at all. The points dont seem to be holding adjustment. Set the gap and got it to start. A friend of mine has some NOS gm points from the 60s so I'm gonna pick those up and try swapping those.
     
    Last edited: Sep 23, 2019
    lothiandon1940 likes this.
  12. Joe H
    Joined: Feb 10, 2008
    Posts: 767

    Joe H
    Member

    I just rebuilt a GM distributor for a '71 Pontiac TA. I used new store bought points and condenser. It would not make a decent spark above 3500 rpm on my distributor machine. Found a NOS set of Delco's at a swap meet and put them in place. Not only could you hear the difference due to the heavier spring, the spark sat right on the money from idle right to 6500 rpm with no problem. In a last ditch effort if the NOS don't pan out, double up the spring and see if that helps.

    I had a '62 Pontiac tach in a '66 Mustag 289, used what I had, that caused a no start issue. Unhooked the tach, fired up and drove home. Tach went back up on the shelf.
     
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  13. bighemifan
    Joined: Feb 27, 2016
    Posts: 13

    bighemifan

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  14. wicarnut
    Joined: Oct 29, 2009
    Posts: 3,230

    wicarnut
    Member

    Be curious to read solution when problem is solved, back in 60's, first car I put together at 16, swapped in engine, ran good, burnt points quickly, sharp man at parts store asked me about the ballast resistor, he showed me one, told me to look see, I did not have one, installed it, problem solved. do you have one wired in ?
     
  15. I have a brand new ballast put in. It really makes no sense. Hoping the NOS points will help
     
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  16. wicarnut
    Joined: Oct 29, 2009
    Posts: 3,230

    wicarnut
    Member

    If different points/ condenser doesn't help, check continuity on all your primary ignition system wires pulling wiggling them to be sure not broken under insulation, had that happen to me years ago, car would shut off, cool off/start and run till warm. weird deal, took a while. Your Ignition switch new/good, all the normal stuff check, cap, rotor, plug wires, coil. All your grounds.
     
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  17. Truck64
    Joined: Oct 18, 2015
    Posts: 3,595

    Truck64
    Member
    from Ioway

    If the distributor itself is all clapped out they will never read the same twice. Worn bushing/shaft etc.
     
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  18. I agree completely, but this one is tight, and right. It was in a 62 Chevy truck that was perfectly a preserved time capsule, and only had 19,000 miles on it. I Picked it up when I got the entire drivetrain out of it, when the new owner performed the blasphemy of an LS swap.
     
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  19. KoolKat-57
    Joined: Feb 22, 2010
    Posts: 2,818

    KoolKat-57
    Member
    from Dublin, OH

    Is the distributer getting a good ground to the engine?
    Is the hold down tight and making good contact on the distributer?
    Just a couple of thoughts.
    KK
     
  20. Truck64
    Joined: Oct 18, 2015
    Posts: 3,595

    Truck64
    Member
    from Ioway

    Wow, I suppose you already told the tale, but where did you find that?
     
  21. RMONTY
    Joined: Jan 7, 2016
    Posts: 1,359

    RMONTY
    Member

    You might try doing what I call putting it on life support. Run a basic ignition circuit from the battery with no switches or anything but a single wire from the battery and test from there. No tach, no switch, no nothing, and see how she runs.
     
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  22. Truckdoctor Andy
    Joined: Jan 13, 2017
    Posts: 876

    Truckdoctor Andy
    Member

    Has anyone mentioned just disconnecting the tach wire from the coil and road testing it?......


    Sent from my iPhone using The H.A.M.B. mobile app
     
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  23. Truck64
    Joined: Oct 18, 2015
    Posts: 3,595

    Truck64
    Member
    from Ioway

    That's crazy talk
     
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  24. bighemifan
    Joined: Feb 27, 2016
    Posts: 13

    bighemifan

    Perhaps try a different coil. Sometimes they provide sufficient build up when cold, but when they heat up, they can break down too soon and weakens the spark. Although you still get spark, it may not be sufficient. Had that happen on a 63 390 T Bird. Just quit in Winnemucca Nevada, which in those days was 40 miles past nowhere. Made it a beat up gas station & this ole greasy mechanic pulled out this little homemade spark distance tester attached to a board. Showed me where it was working, but weak by turning a screw that increased the gap. He went out behind the station & come back with an old coil off of a wreck. Screwed it on & eureka. Charged me 2 bucks for the coil & it was still on the car when I sold it years later. Just an easy thing to try.


    Sent from my iPhone using The H.A.M.B. mobile app
     
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  25. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,296

    sunbeam
    Member

    I had a 64 impala with a warmed up 327 with a 6000rpm factory tach and replaced it with a new stewart warner tach and it would break up at about 5000 rpm. Traded it for a factory 7000 rpm 409 tack and every thing was fine.
     
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  26. hotrodtodd1960
    Joined: May 1, 2008
    Posts: 157

    hotrodtodd1960
    Member

    When I built my Willys pick up it had a miss when I got on it , started changing everything one at a time carb , distributor, alternator, key switch, finally found the problem - cheap ass Chinese moon Tach wished I would of changed it first
     
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  27. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,296

    sunbeam
    Member

    How about you remove the tach wire from the distributor side of the coil and see if the problem goes away
     
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  28. Post #11, he tried this and it had no change.

    Is it possible your ignition switch is not up to the task? You said that after cranking with no start, turning key off and on and then pushing the starter button lights it off. Do you have the bypass portion of the ignition/solenoid circuit wired so you get the full 12v to ignition in start?
     
  29. tubman
    Joined: May 16, 2007
    Posts: 4,383

    tubman
    ALLIANCE MEMBER

    When we were developing our 6 to 12 volt tach driver, we fried one of the components on a test unit. It caused the engine to just quit. I unhooked the tach and the car stared right up. On a post-mortem, my partner found the failed components and said "Yeah, that would do it".
     
  30. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,296

    sunbeam
    Member

    People are saying you cant find good points there is a guy on ebay selling new old stock GM UNI points for $10 a set.
     
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