I have a '79 F-150 with a '86 460 in it. The problem is for the past three years,( the entire time I have owned it) I have had an intermittent no spark problem. It will run for months at a time, then 30 seconds, or not at all. I have replaced EVERY ignition component on the truck. Cap, rotor, wires, plugs, ignition coil, entire distributor w/pickup coil, ignition switch, Duraspark box, all of it! I have even cut out the plugs and hard wired the wires. No changes, sometimes it runs, sometimes it doesn't. I have just removed all components and had them tested at two different parts stores, one of them NAPA. The guy at NAPA is VERY good and has never steered me wrong. All components are new, and in good working order. He insists that I have a broken wire, or short somewhere. I also had all components tested at a local electric shop, and again they are fine. They also said I have a wiring problem, and that I should bring it in for $58 an hour. My question is this: Is there a known typical location in the wiring causing me to have no spark. The reason I'm asking this before I start tearing the wiring harnesses apart, is I have a '79 Scout II that I had a tail light problem with several years ago. The harness that goes to the lights is mounted to the bottom of the body tub,on the inside of the framerail from the front, then just in front of the rear axle, it crosses over to the outside. Over time, the body and frame wore through the harness, and insulation on the wires, and obviously causing a short. So I am hoping that there is something similar on my F-150 that you guys may know about. I should also add that the only modification to the truck is the 460, no body lifts or any other reason for me to believe a certain wire or harness has been stretched or strained in any way.Thanks for everything.

Will

 

Your gonna have to check it when it doesnt' have spark. As i recall the ignition box has 2 hot wires, a red and a white. I believe they are both hot while it's running, check them with a testlight while it's working and make sure . then when it dies check them and see if one is dead. If it's dead trace it back to the ignition switch and see if it's hot there.

 

Close Eric, red is hot in "run" and white is hot in "start"

Sniper, all I can think of doing is verify you have a good ground strap from the engine to the chassis and I think I would look to completely replace the wiring from the DSII box to the reluctor coil. I am thinking maybe you have a cracked/corroded wire, most likely between the reluctor and the DSII box. This is the lowest current signal in the entire system and, it would seem to me, the most likely candidate for an intermittent problem such as yours. I would think that the other high current leads, if faulted, would steadily degrade over time and lead to permenant failure.

Then again, about the only thing you haven't replaced is the ballast resistor... so might as well try that to! GL

 

[QUOTE=Ecuri]Close Eric, red is hot in "run" and white is hot in "start"

Depends on the ignition box, some of the aftermarkets swapped the red and white, I've run across it a couple of times. That's why I suggested checking while it is running. Besides, I think it cross feeds while it's running anyway, so both will appear to be hot.

 

What about the ignition switch? I had this problem on my "71 because I had a heavy key ring with a lot of keys. I guess the weight in time wore the switch contacts so that they became intermitten. Sounds like you've tried everything else.

 

I am having the same problem right now. I found this on the web that is helping me troubleshoot my wiring before I start buying parts. Keep us posted as to what you find.

http://users3.ev1.net/~bmarr/duraspa...on_upgrade.htm

 

Check number one, check the wires and contact at the coil, then with an ohm meter, you can check the connection from the ignition module harness terminals to distibutor housing harness terminals, and coil wire terminal. Wiggle the wires while performing the test to verify if there is a short in the electrical system.

Check number two, Check the wires and contact at the ignition switch, then with an ohm meter, you can check the connection from the ignition module terminals to the ignition switch wire. Wiggle the wires while performing the test to verify if there is a short in the electrical system.

Refer to electrical schematic for wire colors and designation.



Other test and information found at: http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0a/50/6e/0900823d800a506e.jsp#hd1-1-6

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0a/50/6e/0900823d800a506e.jsp

 

Well guys, she's on the road!! Thank you for all your help. Sorry it took so long to get back on here; just been busy with the truck (some starter & other problems since) and with the family.
Anyway, I found the problem in the engine harness. Like I said in my original post, I had replaced EVERY ingition component and still had trouble, then I removed all of those components and had them tested at three different shops just to be thorough. After all that, I removed the engine harness and put it on the bench in my shop. I disected it with a razor knife, and slowly began to inspected it. About 12 inches from the distributor plug there was a noninsulated crimp connector that a previous owner or mechanic used to repair the red wire, but did not tape it or insulate in any way. And about an inch down from that on the green wire, there was a bare spot. What was really throwing me off was the fact that the outside of the harness looked just fine.
So I gathered all the proper colors of wire so that I could maintain the factory color codes for ease of any future problems, and made her a whole new harness with all the arms and legs coming off where they should for the water temp. sensor and so on. Everything worked out great, and fires every time.
Elenor (the truck) and I thank you all very much!