Screw car shutting off under power

Discussion in 'PSI Superchargers Tech Questions' started by overkill69, Jul 20, 2014.

  1. overkill69

    overkill69 Member

    Joined:
    May 17, 2005
    Messages:
    826
    Likes Received:
    0
    After 6 blower belts we figured out that the ignition on the car is shutting off and coming back on when the car launches...sometimes it looked like a bucking bronco or the driver pedaling like crazy. After a couple cycles the belt breaks. The car was running very strong until 100ft out. Once it made it to 400ft. This is not rev limiting the ignition is totally on and off.

    The data logger died on the first hit.
    I made a fresh file for the 8973. It was corrupted at the last race.
    By passed the mag kill solenoid
    Ohmed crank trigger
    Changed point s box
    Inspected all the wiring
    Everything except the 8973 went out for inspection 1 race ago.

    Thanks
    Mike
     
    #1
  2. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,630
    Likes Received:
    189
    Mike, you say you have a crank trigger so do you have a crossover switch to switch between the mag and the crank trigger? If so how and where is the switch mounted. Also what do you have for an ignition switch to turn the 8973 switched power and and off? You can also take out that mag kill solenoid because shutting off power to the 8973 will shut down the motor.
     
    #2
  3. overkill69

    overkill69 Member

    Joined:
    May 17, 2005
    Messages:
    826
    Likes Received:
    0
    power

    no switch for triggers
    8973 runs off a fused switch in a dedicated switch panel
     
    #3
  4. overkill69

    overkill69 Member

    Joined:
    May 17, 2005
    Messages:
    826
    Likes Received:
    0
    batt

    I have a small lith ion battery for electronics. On some old data I saw the volts drop to 11.8 when the brake was on. Is this an issue?
     
    #4
  5. john348

    john348 Top Alcohol

    Joined:
    May 29, 2003
    Messages:
    1,348
    Likes Received:
    5
    check your battery connections could have a bad battery
    are you using a capacitor for the power
     
    #5
  6. overkill69

    overkill69 Member

    Joined:
    May 17, 2005
    Messages:
    826
    Likes Received:
    0
    cap

    yes have a capacitor and checked connections
     
    #6
  7. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,630
    Likes Received:
    189
    Most MSD systems will function down to nine volts. Have you tried running it without the crank trigger and using the mag?
     
    #7
  8. Shakedown

    Shakedown Jr. Dragster

    Joined:
    Feb 12, 2005
    Messages:
    182
    Likes Received:
    0
    Cutting off and on

    We had the same problem and the Coil was bad. Put another one on the car and went rite down the track. Sent that one to MSD and sure enough it was bad!
     
    #8
  9. overkill69

    overkill69 Member

    Joined:
    May 17, 2005
    Messages:
    826
    Likes Received:
    0
    power

    I have the capacitor inline which should stabilize voltage swings?
    I was going to run on nothing but mag and internal trigger for the final but I convinced myself the kill solenoid would fix it. It didn't. 150ft feet of the best run ever and then the worst belt destruction ever for the final.
     
    #9
  10. Soldierboy0098

    Soldierboy0098 Active Member

    Joined:
    Feb 17, 2006
    Messages:
    1,417
    Likes Received:
    16
    Mag Kill switch

    Hi Mike,

    Be careful on that, Kenny's car got stuck at full throttle and his 8973 would not shut off when the regular switch was turned off. It may just be how it was wired or something but long story short it made a 280 mph run and stopped a 1/2 mile off in the sand...no joke (Youtube Ken Cruz crash) I put one in for additional piece of mind.

    Best wishes,
    Trevor Sherwood

     
    #10
  11. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,630
    Likes Received:
    189
    Then it was not wired correctly. If you shut off power to the Grid or 8973 then the ignition system shuts off because you have broken continuity between the crank trigger/Mag trigger and the Electronic Points Box so nothing to trigger it.
     
    #11
  12. Joad Donnelly

    Joad Donnelly Member

    Joined:
    Jul 2, 2009
    Messages:
    84
    Likes Received:
    0
    On the kill switch/solenoid thing, when we took the kill solenoid out of the system I figured killing the power to the 8973 would shut the car down. My normal routine is to pull the fuel shut-off then pretty quickly hit a big kill switch which I have wired to the kill solenoid and also to the air shifter to so it will dump the air at the same time. After disabling the kill solenoid for troubleshooting purposes I wanted to make sure I could kill the ignition so when we test fired it in the pits I killed the power to the 8973. Eventually it did shut down but it took a long time and I'm assuming this is because the capacitor continued to power the 8973 for a bit. This normally probably wouldn't be an issue but I like not having the delay. Maybe wiring the switch between the capacitor and the 8973 would eliminate this delayed shut-off? As I'm thinking through what could be causing this I'm thinking it's probably not just a straight power problem because with this capacitor in the system I don't think that the power could be shutting off and then back on to the 8973 rapidly enough to cause the symptoms we are seeing. This problem was first noted after we broke an old belt near the top end and it did smack the points box and the coil. We did change the points box but not the coil so it could still be suspect. Thanks for any ideas.

    Joad Donnelly
     
    #12
  13. aj481x

    aj481x Member

    Joined:
    Jan 27, 2004
    Messages:
    976
    Likes Received:
    18
    The switch needs to be after the capacitor for instant shutdown.
     
    #13
  14. skauto

    skauto Member

    Joined:
    Nov 27, 2008
    Messages:
    248
    Likes Received:
    0
    I had a similar issue and found that the fuse block i was using to protect the grid had its fuse shake loose enough to make and break contact to the grid when i launched the car it shut off and then the nose dropped it took off again, i thought when i had the big dead spot and my foot was to the floor i was going to launch my top end sky high but it just turned back on and away it went, so if you have any check the simple things like fuses and connections first
     
    #14

Share This Page