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HEI Relay problems
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Author:  Derek Townie [ Fri Nov 01, 2013 11:15 am ]
Post subject:  HEI Relay problems
Hi - I have a few questions about adding a relay to my HEI set up...

Last month a took the Town Wagon for it's longest drive yet to the NC mountains. When I went to leave I couldn't get it to fire. Eventually I worked out I had no power to the coil so jumped it directly from the battery...

Now I'm going back through the wiring and tidying things up so decided this was a good time to add a relay to the system. I think I have it wired up correctly and have 11.5v across the coil with key on. When I crank it goes down to 9.5v with no spark out of the coil. Any ideas what could be going on here?

I just went outside to see if it starts if bypassing the relay and much to my horror I see smoke coming from the coil (MSD Blaster 2)... my g/f left the key on when she was cranking it over for me :-( It was probably on for an hour. Is this expected or is there something wrong? Would a fuse somewhere help stop this happening in the future?

Thanks for your help

D.
Author:  wjajr [ Fri Nov 01, 2013 12:08 pm ]
Post subject: 
Yup, key on engine off, coil will melt down after a while.


I'm not sure of this, but I think Blaster 2 coil requires reduced voltage or it will fail.

Can you supply a diagram of how you wired in relay and HEI into your car?
Author:  Joshie225 [ Fri Nov 01, 2013 12:17 pm ]
Post subject: 
I didn't think the HEI module would keep feeding power to the coil without a signal from the distributor. Or maybe the original GM modules do work this way and you have an aftermarket module? MSD coils aren't the best quality nor are the cheap replacement HEI modules. I used genuine, but used GM parts for my HEI conversion Better than the GM coil is the Ford transformer looking coil used with TFI like Standard Motor Products Part # FD478.
Author:  Derek Townie [ Fri Nov 01, 2013 1:06 pm ]
Post subject: 
http://www.flickr.com/photos/35716845@N00/10614852576/

Thanks for your replies.

I've just realized that I forgot to connect the wire to the alternator regulator... could this be a factor? When it stops raining I'll add this back in assuming the coil isn't fried.

As you can see the coil gets power straight from the relay. Is this wrong?
Author:  Joshie225 [ Fri Nov 01, 2013 1:27 pm ]
Post subject: 
Do you really have the negative side of the coil grounded? That would have never allowed the coil to fire and would, indeed, burn up the coil.

The only connections to the negative side of the coil are the C terminal on the ignition module and, optionally, a tachometer. The ignition module turns the coil on and off by closing the path to ground (coil on) and opening the path to ground. With the negative side grounded you will have full battery voltage flowing through the coil full time. You saw the result of that in the form of heat and smoke.

The mounting hole on the module with the metal ring does need to be grounded. This is normally done through the mounting screw, but a ground wire can help.
Author:  Derek Townie [ Fri Nov 01, 2013 1:34 pm ]
Post subject: 
Whoops!! Yes I do. I figured the C terminal was a ground also.. obviously a bad assumption!!

Thanks for your help. I'll remove that pronto and hook it up to the mounting hole instead.

I looked at the coil you recommended... how does the lead to the distributor attach? Do you need a special lead? I've never really looked at these modern ones.

d
Author:  Joshie225 [ Fri Nov 01, 2013 2:21 pm ]
Post subject: 
Thanks for drawing the diagram. That made trouble shooting much easier.

With the Ford coil you need a new coil wire. I had a GM coil with a male terminal and used a spare spark plug wire. Good auto parts stores will often sell single wires. I might get the Ford coil, primary wire connector and coil wire from a wrecking yard and change the distributor end of the coil wire.
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