crazy promag issues

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by overkill69, Jul 20, 2015.

  1. overkill69

    overkill69 Member

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    After a season long battle with misfires, shutting off and broken belts we completely rewired the car and replaced the 8973 box with a grid over the winter.

    Ran last weekend and broke a belt on the first hit.

    The data showed the rpm falling to zero and then spiking right back up twice before the belt broke.

    The grid data showed crazy rpm spikes and it was trying to apply limiters to them.

    After 3 attempts and lots of parts thrown at it we unhooked almost everything we could.

    It ran clean and took out the #1 qualifier,0

    But we don't know which item fixed it.

    Items disconnected:

    Lahey timing indicator box that supplies data logger with timing info

    4 stage fuel mgmt. solenoids and timer box. Left the 2 step solenoid functional,

    Very old autometer tach

    Basically everything was unhooked from the tach signal wire to the grid.

    Can noise backfeed into that wire and make the ignition go nuts?

    Everything on the car has been replaced twice and I already talked to Lahey.

    We won the race from last qualifying position!


    Thanks for any thoughts
     
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  2. Mike Canter

    Mike Canter Top Dragster

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    When you were having the issues before you disconnected everything did you look at the data recorded within the Grid on MSDReView? Especial Ignition In, Ignition Out and Voltage. If not that data is still in the Grid and you should go back and look at it.
     
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  3. HootersFunnyCar

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    Tach

    Is it an inductive mag tach or a green wire tach? I have seen a green wire tach mess up a MSD ignition box it would limit the rpm and sound horrible popping and farting down track. It was not on a Promag but it could be screwing up the grid???
     
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  4. overkill69

    overkill69 Member

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    grid

    Green wire tach. I have confirmed that promag sprintcars can have a bad tach kill the engine through the output wire.

    Mike, the grid showed a nasty ignition in/out signal. I forgot to configure to log battery volts but we have changed the battery and all power wiring plus we used to run the big capacitor and still had the issue.
     
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  5. Mike Canter

    Mike Canter Top Dragster

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    The recorded Ignition In is the ignition trigger signal coming from either the crank trigger or from the lower wire on the generator which is the internal trigger depending on what you are running. If that signal is bad then the problem is interference being picked up on that input and NOT something in the Grid. Crap In, Crap Out. The only thing that the Grid does to that signal is to delay it to retard your timing. Yes, and it uses that pulse to make an rpm signal out. If you are running a crank trigger then unless you have a shield that is grounded you will pick up noise on that input signal which makes the Points Box think it was triggered. This will cause popping, backfiring, belt breakage or destroy the motor. It also can happen using the trigger in the generator because that wire from either the crank trigger or the generator trigger runs a long way to the Grid and can pick up RF or EM interference. It could be that one of those devices you disconnected is acting as an antenna to this interference and is passing it on to this gray input wire. That gray input wire and the white output wire should not be run next to any other wire and kept well away from the coil and plug wires. Outputs such as the tach signal are normally protected from back interference or loading. The most that can happen if you overload the tach output is to totally loose the tach signal but it will not change the ignition trigger signal and like you said the IGNITION IN is bad so it can't be the tach being plugged into the Grid.
     
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    Last edited: Jul 21, 2015
  6. overkill69

    overkill69 Member

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    grid

    interesting..We have shielded Lahey wiring on all the trigger stuff with good routing and grounds.
    We had issues on the mag trigger and crank trigger but they run through the same wire back to the grid. Everything has been replaced and bench checked several times.
    I had 2 8973 boxes in the car so I do not blame the grid.
     
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  7. Mike Canter

    Mike Canter Top Dragster

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    Something is acting as an antenna. Since it has happened on both the 8973 and the 7730 is even more indication. The problem can bve even though it is a shielded cable if it is run too close to the coil, the coil wire or plug wires it is still going to get through. I would check very carefully on the routing of the crank trigger wire, the gray wire to the 7730 and the white wire from the 7730. Are they run by themselves or are they next to other wires/cables? This random firing of the Ignition system caused nitrous cars in the 1990's to switch to Mallory systems until they found out it was non shielded crank trigger cables. We used to send our 7AL2s and 7AL3s back to MSD and they would be returned saying nothing wrong with them. We destroyed motors because of this problem. Nobody ever told us that MSD had a special new shielded crank trigger wire that fixed the problem. I believe MSD still provides a non shielded crank trigger cable with the crank trigger and Digital 7.
     
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  8. Joad Donnelly

    Joad Donnelly Member

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    A few additional questions. So you're saying that the ignition in signal will stay consistent on the Grid logger as long as the Grid is on and the engine is spinning over regardless of what the output side is doing? So say if we look at it when it's on the 2-step, will have a consistent pattern the whole time? How about the ignition output data, will it be a lot different in the same 2-step condition when the limiter is holding the engine back? When you mention the gray wire, about are you talking about the shielded cable running from the crank trigger (or mag trigger if we're hooked up to it for troubleshooting)?. The Grid came with a long unshielded output white wire that is used to trigger the ignition, it seemed weird to me that this wire was not shielded. What's your thoughts on this?

    Thanks Mike!
    Joad Donnelly
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    The IGNITION IN is from whatever source you have trigger the ProMag and will remain consistent only if the RPM is constant. As you increase in motor RPM then the trigger (which will look like a square wave if you zoom in enough) will get closer together. When on the Two Step the Grid is randomly shutting off the output triggers and you will see a random pattern on IGNITION OUT. If you have a intermittent crank trigger then you will see blank spaces on the IGNITION IN and the IGNITION OUT. If the Grid input voltage drops down far enough (when a solenoid turns on) to shut the Grid down then you will see a good IGNITION IN but an intermittent IGNITION OUT. It is good to monitor the Grid input voltage. If the motor will not fire then you can change the Grid start recording RPM from 3500 down to 100 rpm then try and start the monitor and after it doesn't start you can look at the Grid recorded data and see if the crank trigger input on IGNITION IN is there or not. The bad thing is the Grid doesn't tell you anything about the coil or Points Box.
     
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  10. rb0804

    rb0804 Member

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    Have you had your coil sent out and checked out lately or have you tried a different one?
     
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  11. Joad Donnelly

    Joad Donnelly Member

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    Yes to both. The first one checked out good but we tried a different one anyway, the problem remained the same.

    Joad
     
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  12. texas racer

    texas racer New Member

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    ..is there any grounds wires from the heads ..to coil negative ...then back to all the electronics
    and battery ?
     
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  13. Joad Donnelly

    Joad Donnelly Member

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    Pretty much yes to all the grounds you mentioned. I didn't have the ground wire from the crank trigger shield tied into the common ground most everything else is tied to, which goes back to the battery. I plan on doing that before we go back out.

    Joad
     
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  14. Mike Canter

    Mike Canter Top Dragster

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    But does the crank trigger shield ground go to ground right now?
     
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  15. Joad Donnelly

    Joad Donnelly Member

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    I have the crank trigger shield grounded at a standalone chassis ground point but this point isn't directly via a wire path directly back to the battery as most of my other ground points are on the car. It is simply a chassis ground at this point but I plan on tying it into the ground path that is tied directly to the battery. Is there any reason not to have the motor ground jumper wires and the coil ground jumper wire all tied into a one common ground point that is wired directly to the battery?

    Joad
     
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  16. Mike Canter

    Mike Canter Top Dragster

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    That should be enough ground for the crank trigger because you are just ground the shield and not creating a return path to the coil as with the head grounds.
     
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  17. turbo69camaro

    turbo69camaro Member

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    I have a long tab welded to the front part of the chassis with multiple 10-32 tapped holes all of my head,coil,points box,crank trigger shielding wire grounds all bolt up to it.My crank trigger wire runs along the lower frame rail and there are no wires even close to it
     
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  18. GottaGoFaster

    GottaGoFaster New Member

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    Hi All--
    I know this is string is an older post--but does anyone know if MSD has improved their noise filtering with the Grid (with ProMag44)? I have been having issues very similar to this string's descriptions, had been thinking it was a very rich condition. But after reading this string, i am thinking i need to re-route and better shield some wiring.
     
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  19. Mike Canter

    Mike Canter Top Dragster

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    The only one that needs careful routing is the one from the crank trigger to the Grid. It needs the shielding to be grounded and to route it far away from the high voltage coil wire. Plug a laptop into the Grid and open the View software and go to the top of the page and open Aquisition and download the last run and look at the engine rpm and Ignition In which is the signal from the crank trigger and the Ignition out which is what is going out of the Grid. Zoom in and look at the square wave trigger and see if there are gaps.
     
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  20. GottaGoFaster

    GottaGoFaster New Member

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    THanks Mike--i did download data from my last run. There seems to a "major" and a "minor" square wave on the ign input. I tried to upload a couple screen shots. What do you think?
     

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