Ignition Help
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Ignition Help
I have a 77 F250 with some problems sparking. I think the problem is the ignition boxs. The plug that feeds the distributor and the coil has two wires with power. Shouldn't only have one.
I could use some help.
I could use some help.
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Thanks for the help. I just want to make sure I understand. Are you talking about the plug that has two prongs in side that run back though the firewall? Or are you talking about the other plug that has four prongs? It is the four prong plug that I have power at twice. I thought that I should only have one wire with power which ran to the distributor. Doesn't my coil also get its negative wire from this plug? The wiring diagram I have doesn't help much.
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From: Virginia
The dist has a ground wire inside it. This is the ground for the whole ignition system. The wires from the dist to the ignition box have a pulse type signal they send to the box (almost like ac) and I doubt you will get a meaningful reading with the truck not running.
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Thanks for the help. It sounds like I have a bad ignition box.
I didn't think I should have 12 volts coming out of that box twice.
The signal wire you are talking about runs to the coil as well?
When I test the coil, I have 12 volts on both sides- this isn't right?
I didn't think I should have 12 volts coming out of that box twice.
The signal wire you are talking about runs to the coil as well?
When I test the coil, I have 12 volts on both sides- this isn't right?
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From: Virginia
The module fires the coil. The + of the coil is hot all the time, the negative of the coil is grounded by the module to make the spark. You should see the negative of the coil float up to 12 volts, and then drop down to near zero when the engine is cranked.
The pick-up in the dist goes directly to the module. All it does is tell the module when to fire the coil.
The pick-up in the dist goes directly to the module. All it does is tell the module when to fire the coil.
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Thanks again for the help. I'm going to replace the ignition module this weekend and hope for the best. Is there a way to test the coil and the distributor? All of these parts have been replaced in the rebuilding of the truck, but it hasn't run since and I don't want miss anything I could test.
Brian
1977 F-250
Brian
1977 F-250
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This thing is driving me crazy. I just replaced the ignition module to day. Only to find that it has no power coming out of it when the engine is in the run position. I have power coming into it, but nothing going back out. Does the module only send power out when the motor is actually turning over? And help would me great, I have to get this truck out of my friends drive way.
Thanks Brian
77 F250 351M
Thanks Brian
77 F250 351M
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From: Virginia
The module does not send power out. The module grounds out the green wire(tach) on the coil. This completes the circuit through the coil, because the positive of the coil(bat) has 12 volts on it.
Do you have 12 volts on the coil positive(bat) with the key in the run position?
When the engine is cranked, do you still have 12 volts on the coil positive(bat), and do you get a up and down voltage on the coil negative(tach)?
Do you have 12 volts on the coil positive(bat) with the key in the run position?
When the engine is cranked, do you still have 12 volts on the coil positive(bat), and do you get a up and down voltage on the coil negative(tach)?
Last edited by Franklin2; Mar 18, 2004 at 11:06 AM.
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OK So the ignition module that had power coming out must have been broken, and the new one that has no power coming out is correct. Thanks, that helps. At the coil I have 12V on the positive. I also have 12V on the negative side as well and that is with or without the wire from the ignition module in place. I have a felling that the coil is shot as well as the module inside the Mallory Unilite distributor. Thanks for that diagram, much better then the one I have.
Brian
77 F250
Brian
77 F250
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From: Virginia
When you crank the engine, the 12 volts on the negative side should appear, then disappear, and then re-appear over and over as long as the dist is turning, which brings up a good point;
Have you looked inside the dist while the engine is cranking? It may not be turning, meaning a mechanical problem in the engine. It happens.
Have you looked inside the dist while the engine is cranking? It may not be turning, meaning a mechanical problem in the engine. It happens.
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No I have not checked to see if the dist is turning when the engine is cranking, and I don't no why I missed that one. I will check that to night. One more question for you. Does the dist need 12V, if so where does it come from.
Thank again
Brian
77 F250
Thank again
Brian
77 F250