Question on Starting on MAG then switch over to 8973

Discussion in 'PSI Superchargers Tech Questions' started by pentastarrail, Mar 20, 2012.

  1. pentastarrail

    pentastarrail Top Dragster

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    Hi Guys,

    I have an issue with the engine starting (526 hemi, 1471).
    It starts fine when I use the MAG only but when I try to go thru the MSD 8973 it may start or may not. I have 2 - 16 volt batteries (32 volts) to the starter.
    Like I said sometimes it fires other times it just spins over.

    Does some one make something that I can plug in between the 8973 and mag so it starts on the mag and then I can flip a switch to the 8973?
    This is in a TD.

    Thanks in advance.
    Frank
     
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  2. Don Onimus

    Don Onimus New Member

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    Starying

    Hi Frank, What do you have the timing @? How long are you spinning it over befpre you hit the switch? Maybe Mike Canter can help you answer that question. Don
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    Frank, do you have a crank trigger and when you start it just on the mag then do you bypass the crank trigger? If you have a crank trigger then have you phased the rotor in the mag. The easiest way to do this is to be on the mag only then set the ignition timing to where you want it then go to the 8973 and cranktrigger and set the ignition timing to the same degrees. Do you have the Start Retard at ZERO in the 8973? If you have a crank trigger then what is the air gap set at. Dave Leahy at http://www.electrimotion.com/ does make a bypass switch for starting BUT it is to take the crank trigger out of the circuit during the start and not the 8973.
     
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  4. JustinatAce

    JustinatAce Member

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    You shouldn't be having any issues starting with the 8973 as it is basically just a timing/shift light controller and rev limiter that tells your points box what to do. Double check your baseline settings and make sure that the power supply to the 8973 is staying on when you're starting. It should just flash the shift light when you turn it on, then you should be good to go.

    Also, are you using any sort of timing monitor or crank trigger? We've had issues not spinning fast enough before with the starting on the crank trigger if the batteries were drained a bit and we've had to switch from mag to trigger before, but that's with 48v in NHRA TAFC trim.
     
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  5. pentastarrail

    pentastarrail Top Dragster

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    Starting

    Thanks for the replies guys.
    I should have given that info earlier.
    No crank trigger.
    Zero start retard.
    Timing locked at 25
    Yes, the shift light does flash when I turn it on.
    I spin it for about 10 seconds before I hit the ignition.

    It's frustrating because sometimes it lights and sometimes it doesn't.
    When I disconnect the 8973 and use mag only it starts EVERY time.
     
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  6. TWD

    TWD Blown alky

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    Check the cranking speed. If I'm correct the later generation of 8973 has a 'start-inhibit' function which just does not allow it to fire below 250 rpm. And with a digital system 249rpm just will not be enough...
    You can put a switch in there to bypass the 8973 for starting purposes. We used a simple flickover switch to connect the internal trigger directly to the mag for starting and with a flick of the switch (dual pole change over) we connected the 8973 signal to the mag which was running from the crank trigger. You can even run different base timing if you like and using a crank trigger is a good idea anyway.
     
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  7. Mike Canter

    Mike Canter Top Dragster
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    You should hook up a laptop to the 8973 then watch the MONITORS in the upper left quadrant of the screen and see if a message comes on when it does not start or see if it shows a different set of messages between when it does start and when it doesn't start. The only other thing is that one of those 16 volt batteries is bad and that is the one you are using to power the 8973. If the voltage gets too low then the 8973 powers down, try swapping the two battery positions and see if that makes a difference. With two good 16 volt batteries I am sure you are spinning over fast enough to be above 250 rpm. Also that is a mag restriction and not a 8973 restriction.
     
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  8. pentastarrail

    pentastarrail Top Dragster

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    Starting

    Thanks again guys.

    What blows my mind is that it starts EVERY time on the mag.
    But I roll the dice when the 8973 is connected. I've tried another 8973, it does the same thing. I ran ALL new wiring, same thing. I swapped the 2 - 16 volt batteries out for 2 brand new ones, same thing.
    I'll check the "monitors" myself and see if I see anything, (I actually had an MSD tech, Carlo, helping me at the Chicago National), he was watching the monitors when we tried to start it, he didn't see anything.

    One thing we did notice is that it MAY fire once initially on the 8973 BUT if you turn it off then try to re-start it it will just spin and never lite. Then I'll just plug the mag into itself and it fires right up.

    I have tried a new coil, a new mag, a new points box, seperate power source (battery), 3 - 8973's, all new car wiring, seperate 8973 wiring, adding more grounds, grounding 8973 directly to the battery with a seperate wire. Still won't fire.

    Do you think if I swap to a "GRID" it may help me?

    Sorry for the long post but this has me VERY frustrated.
    Thanks again.
    Frank
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    Frank, since you have swapped 8973's and it didn't fix it I doubt that going to a Power Grid will fix it. What I would do is put a voltmeter on the power into the 8973 or and watch what happens to the voltage in when you try and start the car. See what it drops down to. Let me know what happens.
     
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  10. TADHemiracer

    TADHemiracer Member

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    Starting Issues

    Be sure the "MAG COMP" in the 8973 is set to "AUTO".
     
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  11. TWD

    TWD Blown alky

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    Something similar from the past including a note on the wiring:
    http://www.msdignition.com/forum/showthread.php?p=40248#post40248

    I know for a fact that our engine did start on the mag trigger at 190 rpm and it would not using the 8973 with the crank trigger. I agree that two 16V batteries should be enough, but better safe then sorry so I'd check the speed monitor with the laptop.

    Another old comment from MSD tech I found: there's 4 degrees of retard with the 8973 installed which may make it more difficult to start.
    "Cranking RPM's SHOULD BE NO LESS THAN 250 RPM’S. What happens is that you have the added 4 degrees from the 8973, which in turn takes more RPM’s to fire up the mag. One other thing that is crucial, is that the START RETARD has to be set at zero, or the RPM’s would be an additional 100 RPM’s to fire it(350~400)."
     
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    Last edited: Mar 21, 2012
  12. Mike Canter

    Mike Canter Top Dragster
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    TWD, that 4 degrees retard is transperant and due to a built in delay for the processor chip in the 8973. Yes, if you switch from just on the mag to the 8973 you will see 4* difference but you set the timing when on the 8973 and the 4* retard is no longer there when on the 8973 but if you switch to just the mag and check it with a timing light then you will see 4* advance. It fires at the timing you set it at. In this case because he is switching back and forth he will see the timing change. If you set the timing when on the 8973 it is not more difficult to start because the timing is right where you want it without any degrees added or subtracted. That MSD tech was confused.

    Wow, this is my post number 2400. I think I spend too much time here:cool:
     
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    Last edited: Mar 21, 2012
  13. TADHemiracer

    TADHemiracer Member

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    Mike Canter Spending Too Much Time On ITA

    Hey Mike, Don't stop posting now. I still have a lot to learn!!!
     
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  14. pentastarrail

    pentastarrail Top Dragster

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    Starting

    Thanks again guys.

    Mike, you better not go anywhere :cool:


    Frank
     
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  15. crdafoe

    crdafoe Member

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  16. Mike Canter

    Mike Canter Top Dragster
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    I believe that switch over box that Spud makes is to take the crank trigger out of the circuit on start and not to switch from 8973 to mag and back. MSD makes one, Electrimotion makes one and so does Spud. They all do the same thing.
     
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  17. aj481x

    aj481x Member

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    Just curious, isn't 10 seconds a long time to crank? Also, are you starting on gas or alcohol?
     
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  18. pentastarrail

    pentastarrail Top Dragster

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    Starting

    I talked to Dave, as was mentioned he has a switch for the issue I'm having so that will be my next investment.

    I've tried 10 seconds down to just a couple, no difference.
    Trying to start it on gas.

    Thanks again guys.

    Frank
     
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  19. Don Onimus

    Don Onimus New Member

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    change switch

    If you are looking for the auto one, give me a call or e-mail me. I have a almost new one. Don donimus333@yahoo.com. 267-625-0891
     
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  20. ibaddlizzard@aol.com

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    we have to use one of daves switch overs too... ours wont start about half the time on the trigger and it always wont start under the tower if i dont switch it to mag first then switch it back to trigger ....Doc
     
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