73 390 Ignition
Senior User
Joined: May 2001
Posts: 194
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73 390 Ignition
Ok, Fuel pump works great. New brass cap and rotor, plugs are pretty foul, but I would think they would spark. It has a new coil but no spark is getting to the plugs, infact I don't think any voltage is going through the coil. It has a new battery as well. I ran a wire from the battery to the pos coil terminal and I still couldn't get it to fire (I can't confirm if the plugs were getting spark or not though). I have decided that my new coil is a bad coil. Other than that I am fresh out of ideas. The engine cranks just fine, it just won't fire. (Just in case)The guy wired the pos coil to the ignition and the neg coil to the distributor. Please help.
Thanks
Aaron
Thanks
Aaron
Senior User
Joined: Dec 2000
Posts: 435
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From: Nebraska Farm
73 390 Ignition
[font size="1" color="#FF0000"]LAST EDITED ON 23-May-01 AT 08:55 AM (EST)[/font][p]Make sure the points are breaking and firing the coil. A few months ago there was a few posts about testing a coil. I think you can take a test light from + to - and crank the engine, if the light flashes, your coil is good. Somebody I'm sure remembers this post better than I do.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
The post was way back in Dec. search for 'ignition woes' as the subject and this would explain what to do.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
The post was way back in Dec. search for 'ignition woes' as the subject and this would explain what to do.
Senior User
Joined: May 2001
Posts: 194
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73 390 Ignition
>Make sure the points are breaking
>and firing the coil.
Maybe this is a dumb question, but I thought it went the other way around, I though the coil sent the fire to the points. i.e. coil to rotor, rotor to points, points to plug.
Please elaborate.
Thanks
Aaron
Postmaster
Joined: Apr 2000
Posts: 2,838
Likes: 6
From: SD
73 390 Ignition
[font color=red size=2]Here's the way I understand it to work, I could be wrong - who knows... The coil builds up power while the points are open, then the points close and ground the coil, which releases the built up power to the rotor which sends it to the spark plug, giving you a spark.
That's how it works in my head, is that correct?
Marty
"Cleverly Disguised as a Responsible Adult"[/font]
That's how it works in my head, is that correct?
Marty
"Cleverly Disguised as a Responsible Adult"[/font]
Logistics Pro
Joined: Feb 2000
Posts: 3,565
Likes: 9
From: Sun River St. George
73 390 Ignition
Battery voltage to the + side of the coil. The points are a ground and the - wire from the coil connects to ground through the points. Points closed, coil grounded, electromotive force builds in the coil, points open the EMF has no place to go and discharges through the coil wire, rotor, cap lug, plug wire, to plug (which is now the ground). If you take a wire and connect it to the - terminal of the coil, apply battery voltage to the + terminal, and touch the - wire to the engine block, and break the connection quickly the coil wire will fire. Do this quickly and you are doing what the points do. Turn on the key, and open and close the points with a screwdriver. They should snap and have a little spark. Hold the coil wire near the block and have someone turn the engine over, should have a "Big Blue Spark" 20,000 + volts of EMF. The coil wire spark should snap, almost hard enough to take paint off. Many coils do not use the full 12 volts of battery voltage so if you have six or eight volts with the switch on its OKAY. Some use 12 volts for starting and less for running.
William in Atlanta
William in Atlanta
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Senior User
Joined: Dec 2000
Posts: 435
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From: Nebraska Farm
73 390 Ignition
William has it exactly right. The coil builds and stores the power when the points are closed, when they open, all that stored energy needs a place to go. Right to the plugs.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
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73 390 Ignition
Aaron:
Wait a second.... there isn't any high voltage going through the points..... the points make and break a circuit that is less than 12 volts...... They certainly do not pass high voltage. It's the collapsing field (points breaking) of the primary that induces the secondary (spark across the plug gap). The spark occurs when the points OPEN!
Adam
Wait a second.... there isn't any high voltage going through the points..... the points make and break a circuit that is less than 12 volts...... They certainly do not pass high voltage. It's the collapsing field (points breaking) of the primary that induces the secondary (spark across the plug gap). The spark occurs when the points OPEN!
Adam