timing moving on crank trigger

Discussion in 'PSI Superchargers Tech Questions' started by scd, Apr 18, 2010.

  1. scd

    scd New Member

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    timing moving on crank trigger it is not jumping it just slowly pulls out 3 to 4 deg from idle to staging rpm 5500 the trigger is a msd the wheel is a rcd mounted on crank hub with trigger mounted to crank support had to install the msd crossover switch because the engine would not fire on the trigger all help or ideas appreciated
     
    #1
    scd, Apr 18, 2010
  2. Mike Canter

    Mike Canter Top Dragster
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    Is this a ProMag 44? What other ignition control boxes are you using? What kind of timing light do you use? Does the light have a timing adjust dial on it? Have you tried a different timing light?
     
    #2
    Mike Canter, Apr 18, 2010
  3. Bob69

    Bob69 Member

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    Is cross over switch wired in correctly?
    Does it do the same bypassing crossover switch with trigger in Mag only
     
    #3
    Bob69, Apr 19, 2010
  4. scd

    scd New Member

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    it is a pro mag 44 i have tried several lights the best one of the three i have tried is don zig i can order a dif one the crossover switch is wired one side to the mag pickup the other to the trigger and the primary back to the mag
    thanks
     
    #4
    scd, Apr 19, 2010
  5. Mike Canter

    Mike Canter Top Dragster
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    The other question is if you have phased the rotor on the mag. Doesn't have anything to do with the timing changing but may with the hard starting.

    Do you use a 12 volt, a 16 volt or a 24 volt battery to start it?

    Is this a straight ProMag or do you have a 8973 with it. Have you put an extension on the crank trigger cable?
     
    #5
    Mike Canter, Apr 19, 2010
  6. scd

    scd New Member

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    16 volt block mounted starter had to add around 12 inches to trigger leads running thru a 7531 but it does the same bypassing 7531
    thanks
     
    #6
    scd, Apr 19, 2010
  7. Mike Canter

    Mike Canter Top Dragster
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    When you added the 12" did you use shielded cable with the shield grounded to the chassis? This is very important. Did you make the cable yourself or buy it from MSD or Leahy?

    When you bypasses the 7531 did you still use the crank trigger wire extension?
     
    #7
    Mike Canter, Apr 19, 2010
  8. scd

    scd New Member

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    i added the 12 inches myself no ground just cliped the end and added 12 inches of wire twisted together soldered the end back on when i bypass trigger i still hook trigger back to 7531 for my tach signal
    thanks
     
    #8
    scd, Apr 19, 2010
  9. Mike Canter

    Mike Canter Top Dragster
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    A couple of things. If for some reason the wires from the crank trigger got crossed in the extension then the timing will move and be erratic. It is worth double checking. The other thing is that using an unshielded cable can result in that extension being an antenna to Electromagnetic Interference (EMI) from the plugs firing or anything else electrically and can cause random firing or the timing to move. This is a known problem on crank triggers used with the Digital 7s and with the 8973 mag controller and has been responsible for the destruction of many a motor. You should find some shielded wire and replace that 12" section and run a wire from the shield to chassis ground. All the MSD crank trigger extensions are shielded and grounded.
     
    #9
    Mike Canter, Apr 19, 2010
  10. Iron Mike

    Iron Mike New Member

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    and only earth one end of the shield. If you earth both you can get Earth loops and cause more problems.
     
    #10
    Iron Mike, Apr 19, 2010
  11. scd

    scd New Member

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    checked the the trig to be shure the wires did not cross when i added extension and it was correct i will remake the trigger leads does it matter which end i install ground on? also i would love to do away with crossover switch but could not get to fire on trigger, rcd wheel big msd trig 16 volt block mounted starter with a psi screw seems to rotate over fast enough that it would fire trig but it will not, thought about trying a lehay trig what should i try to do so i can eliminate crossover switch
    thanks
     
    #11
    scd, Apr 20, 2010
  12. Mike Canter

    Mike Canter Top Dragster
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    If the mag rotor is not phased right on or real close then it may not start. If you use a pointed rotor vice a flat tip rotor can throw it off even more. Also if you use start retard in the 7531 it will throw the rotor phase off so the spark can't jump the gap. Can't use Start Retard on a ProMag. According to MSD the reason some cars only start with a crossover switch is that out on the edge of the crank trigger wheel the speed the magnets are moving is not fast enough to produce a trigger.

    It makes no difference at which end the shielded cable is grounded (or earthed for Iron Mike)
     
    #12
    Mike Canter, Apr 20, 2010
  13. scd

    scd New Member

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    the method i have been using is fire on the mag set mag timing at 28 deg switch over to trigger while engine is running set trig on 28 no start retard set in 7531 you can bypass 7531 and hook trig straight to mag and it will not fire on mag i thought the phasing would be close since both were set on the same timing my rotor is pointed not square
    thanks
     
    #13
    scd, Apr 20, 2010
  14. Mike Canter

    Mike Canter Top Dragster
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    Setting the mag and crank trigger like that works for rotor phasing. A wide tip rotor may or may not help. Maybe when you replace the rotor next time you should try a wide tip (BBF Rotor) and see if it helps.

    When you set the mag timing then switched over to the crank trigger and set the timing you did that with the 7531 in the circuit...correct? The 7531 will cause 3-4 degrees retard over no 7531 because of internal processing time delay, this retard (delay) is normal.
     
    #14
    Mike Canter, Apr 20, 2010
  15. topalky511

    topalky511 Member

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    I had this exact same problem 2 weeks ago on an outlaw 10.5 car, 471ci short deck hemi, bae and screw, we run a pro mag 44 with an rcd trigger wheel and leahy trigger, also with 8973 and leahy switch box.
    same deal start the car on mag set at 28 degrees, switch to trigger and make sure its at 28 then i bought the rpm up and it retarded slowly back 5 degrees at 6000 rpm still have that steady timing with a crank trigger just retarded slowly.
    It was a fluke that i checked it as i usually only bring up the rpm when checking the mag and i just switch to trigger and check it at idle.
    The wiring harness on the switch box had been extended around 12 inches so i disconected the switch box and no more problem, we where lucky enough that our car started on the trigger all day and it has a 24 volt on board starter.
    As for the reason the car wont start on the trigger could the cap not be phased correctly to the mag, you may have it start and run ok on the mag but what if the rotor button isnt phased correctly it will run on the trigger ok when its running and switched over, but with that slow crank speed maybe its off just enough, also what gap are you running from the trigger to the wheel, leahy recomends 0.080"-0.090" but the small instruction sheet says it may need to be closer for slower cranking cars
    hope this helps
     
    #15
    Last edited: Apr 20, 2010
    topalky511, Apr 20, 2010
  16. Iron Mike

    Iron Mike New Member

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    Mike,

    Agreed either end but not both.
    Earthed = Aussie Sparky talk

    Tyson.
     
    #16
    Iron Mike, Apr 21, 2010
  17. cato

    cato New Member

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    Timming unstable

    Have you checked ujoint on your RCD offset drive. Some of these have failed
     
    #17
    cato, Apr 24, 2010
  18. scd

    scd New Member

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    we did all the above changes and no change wrote over current file in box with 7531 v09 defalut in file menu and made the changes for the mag and the problem went away the file had become corrupt
    thanks
     
    #18
    scd, May 4, 2010

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