burning out ignition coils
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Joined: Jan 2003
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From: Vancouver
burning out ignition coils
Son has a '80 F250 4wdr w 400 2 barrel. His truck burns out ignition coil after 500 to 1000 miles. Is there an incircuit voltage dropping resistor in the 12v feed to the coil that heats up and increases resistance or is switched out by starting circuit? If so, where located?
Red alternator electrical dash light stays on continually. Truck electrical system was supposedly checked by two shops and both tell him there are no problems with ignition or electrical system!! Battery does stay charged.
Engine was pulled and rebuilt by prior owner just prior to problem starting and son buying truck. He lives 100 miles from me so looking for possible solutions before I drive to take a look at it.
Cliff
Red alternator electrical dash light stays on continually. Truck electrical system was supposedly checked by two shops and both tell him there are no problems with ignition or electrical system!! Battery does stay charged.
Engine was pulled and rebuilt by prior owner just prior to problem starting and son buying truck. He lives 100 miles from me so looking for possible solutions before I drive to take a look at it.
Cliff
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Joined: Nov 2002
Posts: 9,987
Likes: 7
From: Memphis, TN
burning out ignition coils
Put a voltmeter across the battery with the engine running & see if it's between 12.8V & 15V. If it's too high, check the alternator & voltage regulator.
Get a Haynes manual and look at the wiring diagrams in the back - they'll show the alternator circuit and the coil circuit.
Get a Haynes manual and look at the wiring diagrams in the back - they'll show the alternator circuit and the coil circuit.
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Joined: Jan 2001
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From: Virginia
burning out ignition coils
https://www.ford-trucks.com/user_gal...oid=12657&.jpg
The top diagram should be the alternator wiring with an idiot light in the dash. The wiring is a little different if you have a factory amp guage. The ignition switch puts 12 volts on one side of the bulb. If the alternator is not working, then the regulator grounds the other side of the bulb, and it lights. If the alternator is working, then the bulb has no ground, and goes out. I would check the green/red wire going to the regulator to see if it is touching metal somewhere. This would make the light stay on all the time. There is also the slim chance that part of the regulator is bad, and part of it is good(charging part).
The lower diagram is a general circuit for the ignition you have. You can see the resistor and where it is placed in the circuit. I have never actually seen this resistor, but seem to rememeber somebody saying it was under the dash, in the harness. The diagrams show a red/lightgreen wire coming off the ignition switch. I would follow this wire, and although it splits off in several directions, one of these branches goes through the resistor, and then out to the ignition coil. If you find somebody has bypassed the resistor because it's bad, I would go and see if you can use one of the large white resistors the stores sell. The book says it should be 1.05 to 1.15 ohms resistance. Make sure you put it in the correct spot in the wiring though, as you will notice this resistor is bypassed during starting, to give a hotter spark.
The top diagram should be the alternator wiring with an idiot light in the dash. The wiring is a little different if you have a factory amp guage. The ignition switch puts 12 volts on one side of the bulb. If the alternator is not working, then the regulator grounds the other side of the bulb, and it lights. If the alternator is working, then the bulb has no ground, and goes out. I would check the green/red wire going to the regulator to see if it is touching metal somewhere. This would make the light stay on all the time. There is also the slim chance that part of the regulator is bad, and part of it is good(charging part).
The lower diagram is a general circuit for the ignition you have. You can see the resistor and where it is placed in the circuit. I have never actually seen this resistor, but seem to rememeber somebody saying it was under the dash, in the harness. The diagrams show a red/lightgreen wire coming off the ignition switch. I would follow this wire, and although it splits off in several directions, one of these branches goes through the resistor, and then out to the ignition coil. If you find somebody has bypassed the resistor because it's bad, I would go and see if you can use one of the large white resistors the stores sell. The book says it should be 1.05 to 1.15 ohms resistance. Make sure you put it in the correct spot in the wiring though, as you will notice this resistor is bypassed during starting, to give a hotter spark.
