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Old 09-22-2010, 12:13 PM
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400sbc Ignition problem/possible dead short!

Just finished building a 400 sbc for my 84 GMC 1500 2wd. I put about 6500 into it and want to get it running so bad I can taste it! Heres my problem:

Installed a new starter and attached jumper cables as my battery has sat for about 6 months; the battery is both side and top mounts which I currently use side mounts. I noticed the cables were arching between the posts when I attached them specifically the negative terminal.

I needed to build oil pressure so I unhooked the green and purple wires coming from my MSD ignition box to the distributor. No spark no start. Got oil pressure, got fuel in the lines, all right lets fire it up. I hooked the green and purple wire connectors back together, cranked it over and it fired immediately but died after a few seconds.

At the same time I noticed a ground coming from the negative battery terminal to the radiator core support was smoking! I replaced it and cranked it and the wire burned up again. I replaced the wire with a huge gauge wire directly from the negative terminal to the chassis. No burned wire but now I am getting no spark from the distributor!

I have an electric fan, disconnected it last night to eliminate it from the problem and still no spark. I was told by a friend that this typically means I have a dead short or a bad ground. Does anyone have any advice? I would greatly appreciate your help as firing this engine up will be a long awaited dream come true.

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Old 09-24-2010, 03:18 PM
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Make sure you have 12 volts going to the distributor MSD box even if it means connecting a jumper from the battery + terminal to the distributor power terminal.

Or GOOGLE --- Testing you MSD ignition.

vicrod
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Old 09-24-2010, 04:12 PM
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Quote:
Originally Posted by bigmt100
Just finished building a 400 sbc for my 84 GMC 1500 2wd. I put about 6500 into it and want to get it running so bad I can taste it! Heres my problem:

Installed a new starter and attached jumper cables as my battery has sat for about 6 months; the battery is both side and top mounts which I currently use side mounts. I noticed the cables were arching between the posts when I attached them specifically the negative terminal.

I needed to build oil pressure so I unhooked the green and purple wires coming from my MSD ignition box to the distributor. No spark no start. Got oil pressure, got fuel in the lines, all right lets fire it up. I hooked the green and purple wire connectors back together, cranked it over and it fired immediately but died after a few seconds.

At the same time I noticed a ground coming from the negative battery terminal to the radiator core support was smoking! I replaced it and cranked it and the wire burned up again. I replaced the wire with a huge gauge wire directly from the negative terminal to the chassis. No burned wire but now I am getting no spark from the distributor!

I have an electric fan, disconnected it last night to eliminate it from the problem and still no spark. I was told by a friend that this typically means I have a dead short or a bad ground. Does anyone have any advice? I would greatly appreciate your help as firing this engine up will be a long awaited dream come true.
That is not a very good place to ground it. Get the ground wire on the frame.
Also when you run the wires for good Ground the motor at the motor don't do like some do and ground it from the transmission, Alum. makes for a very poor conductor. Get the ground on steel to frame, Starter bolt, front of engine to frame. You will have far less troubles with the juice.


Later 35terraplane
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