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 MSD box stock hei FAIL 
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
Well took a good running car and made it run crappy, I put a msd box on it. I know the box is good because I used it to trouble shoot a car with a diff box not long ago, it's a 6al analog that I've owned since it was new.

1st I unhooked the ecm wire like your suppose to then I fired up the car to set the timing and it barely runs. If I set it to stock it'll die and if I turn it up to 30 it'll run but still very crappy and die if reved. It's a 86 TPI car and the box is wired to the stock HEI distributor. I followed the instructions but my setup is slightly diff, instead of the hei in-cap I am using an external cap coil. I also plan to wire the autometer tach directly to the box but forgot to hook it up so that is not the issue.



-white box wire goes to the brown hei
-red to both pinks
-both power wires directly to batt(10ga used & about 6' each of wire from box to batt)
-coil wires to the same TFI coil that was being used with the HEI module
-wires twisted, even used shielded 16ga wire for the coil(could the shielded wire on the coil be the problem?)
-everything spaced and routed apart, box is mounted under the dash more than 6" away form ecm and the power wires are routed to the drivers side while coil wire are out the pass, white signal wire is away from the coil wires.
-wire extensions from box soldered


I didn't grd the coil to the block could that be the problem?


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Wed Sep 14, 2016 4:15 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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Yes, that is the problem. The coil secondary (spark ~ high voltage) must be grounded. It is the center terminal between the + (orange) and - (black) from the MSD box. Normally (in stock OE configuration) it is grounded though the three-wire plug (with pink and brown) black wire to the Phillips screw inside the cap that attaches the module plug and condenser. You must ground that center terminal or the high voltage jumps to the orange and black wires trying to find ground. I have seen the lack of a ground wire there melt the plastic insulation off female spade terminals.

Sometimes when the cap is changed the metal ground terminal stays in the old cap so the coil isn't grounded. I have seen folks pop several of those 5-wire modules trying to figure that out.


Wed Sep 14, 2016 11:47 pm
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Joined: Fri Feb 08, 2013 5:50 pm
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Is it a coil that fits the top of the cap or an adaptor with a coil wire terminal?


Thu Sep 15, 2016 8:19 am
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
external TFI coil

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Thu Sep 15, 2016 1:33 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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Well then, disregard my post.


Thu Sep 15, 2016 2:36 pm
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
Thx for the feedback I kinda thought it wouldn't be.

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Thu Sep 15, 2016 3:25 pm
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
New box didn't fix it.

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Fri Sep 23, 2016 12:18 am
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Run wires inside the HEI, bypass the module and go straight to the pickup coil.I think MSD used to have a harness to do that, but you can make your own. You will have to try the polarity both ways, the polarity that gives you the most retarded timing is correct.


Fri Sep 23, 2016 9:26 am
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Joined: Thu May 08, 2014 7:47 pm
Posts: 236
need to double check the ground side of the box as well. If the box doesnt have a good solid ground, it will run like crap.


Sat Sep 24, 2016 12:34 pm
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
7 pin module doesn't make it as easy Jmark, not saying ti can't be done just not gonna try w/o something checking my re-wiring.

http://chevythunder.com/HEI%207%20pin%2 ... module.jpg

http://gpzweb.s3-website-us-east-1.amaz ... iagram.gif

Both boxes were grounded directly to the batt and the batt has a larger new welding cable ground, other vehicle grds are new or cleaned. I just wired the new box up quick but I know the connections r good. Kinda looks like the timing light clamp is holding the neg on but I assure you it's bolted down.

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Mon Sep 26, 2016 12:10 am
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