Spark/ignition problems
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New User
Joined: Sep 2016
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Spark/ignition problems
Hey guys,
I have a 1986 f150, inline 6 with a TFI IV ignition. I have replaced the coil, entire distributer, and a new ignition/key combo. I had spark, fired it up (disconected the spout), set the timing, shut her down. Pluged the spout back in, fired right up and ran great!! Turned the key off and the truck didn't even try to shut down. Disconected the battery, truck died, now I am back to no spark at all. Any suggestions would be great!!
I have a 1986 f150, inline 6 with a TFI IV ignition. I have replaced the coil, entire distributer, and a new ignition/key combo. I had spark, fired it up (disconected the spout), set the timing, shut her down. Pluged the spout back in, fired right up and ran great!! Turned the key off and the truck didn't even try to shut down. Disconected the battery, truck died, now I am back to no spark at all. Any suggestions would be great!!
Elder User
Joined: Sep 2014
Posts: 862
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From: like subarctic, brrr man!
You say the ignition coil has 12volts across both wires. Not sure what that means, but if your getting 12volts at the coil then something is wonky (thanks capt. obvious!).
When engine is running, coil voltage goes through a ballast resistor or resistor wire which drops voltage to about 8 volts. During Start, the Ignition switch will supply full voltage to the coil bypassing the resistor to help with cold starts. (FYI: On older trucks this function is done by the starter relay/solenoid I terminal.)
Even with the newer electronics, the ignition coil supply circuit is still done this way with the resistor. The other coil wire (Neg or -) heads to the ignition box and pulls to ground similar to a points setup but with a transistor and trigger signals and spout and TFI stuff.
Focus on the coil voltage instead of the electronics! Why is there 12 volts there?
When engine is running, coil voltage goes through a ballast resistor or resistor wire which drops voltage to about 8 volts. During Start, the Ignition switch will supply full voltage to the coil bypassing the resistor to help with cold starts. (FYI: On older trucks this function is done by the starter relay/solenoid I terminal.)
Even with the newer electronics, the ignition coil supply circuit is still done this way with the resistor. The other coil wire (Neg or -) heads to the ignition box and pulls to ground similar to a points setup but with a transistor and trigger signals and spout and TFI stuff.
Focus on the coil voltage instead of the electronics! Why is there 12 volts there?
Last edited by ZarK-eh; Sep 29, 2016 at 09:19 AM. Reason: werds 'n' fermattin'
Lead Driver
Joined: Mar 2008
Posts: 7,188
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From: Near Los Angeles
When engine is running, coil voltage goes through a ballast resistor or resistor wire which drops voltage to about 8 volts. During Start, the Ignition switch will supply full voltage to the coil bypassing the resistor to help with cold starts. (FYI: On older trucks this function is done by the starter relay/solenoid I terminal.)
Even with the newer electronics, the ignition coil supply circuit is still done this way ...
I would find a truck from your year at the J/Y and trace the wires, opening the tape harness with a razor knife, or do some research about the wiring. Also, rather than trying to trace some of the wires on your truck, it might be easier to run new, and then enclose them in the inexpensive plastic harness with the other wires, making it all look clean and oem. Good luck.
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