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1976 Bronco Help Needed- Ignition Box

1K views 6 replies 4 participants last post by  timothale 
#1 ·
Hello all. I am new here and hoping someone can help me with an extremely frustrating situation. I have a 1976 Ford Bronco that has been mostly restored. It has a 351 W engine in it. I just got it back from a guy who was doing some work on it, and have been experiencing a problem i cant seem to solve. I drove it over 3 hours home from the shop and had no problems. Drove it for about another 3 days, when all of a sudden , randomly, it would start bunny hopping. It would do this for a second or two then continue to run strong. it would happen every 25 mins or so at first and then seemed to get worse and closer together. If i were in a low gear the wheels would even chirp as it hopped violently. Sometimes it would even stall. I took it to a mechanic i know, and he said the electronic ignition box was shorting out, causing it to lose spark at times. PIcked up the truck, relieved as i drove it for three days and it ran like a top. Low and behold, same symptoms start coming back. They are getting worse and worse each time again. Couple of things to note, speed seems to have nothing to do with it. It will do it at 55 or 15 mph. I did have the realization that the guy who originally worked on the vehicle, put in a stereo with an amp etc. I checked and the positive battery terminal was a git loose where he added the power for the amp. i started the truck and jiggled it and it sparked a bit. i tightened the cable and took it for a drive. still doing the hop once in a while. Question is- could it have been frying the ignition box and cooked the new one already with the loose cable? was my mechanic on the wrong track in the first place? I know enough about cars to make myself dangerous so any input would be greatly appreciated!! Thanks!
 
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#4 ·
I doubt it , but if its a chinese made knock off, it could be.
I would be suspicious that the coil is shorting out, or leaking high voltage.
The ford modules keep the coil live, and turn off wh en it needs to fire.
That makes a lot of heat and is tough on coils, especially cheap ones.
The GM module has active dwell and only turns the coil on long enough to "charge" it then turns off as needed to fire it.
That is why you dont leave the key on in a ford with durasparks, as they burn coils and control units due to the fact that the "on time " (dwell) is much greater than needed.
 
#6 ·
If you are still having problems, I would suggest looking into a Performance Distributors DUI HEI distributor. This will completely eliminate the overly complicated Ford ignition system with an HEI style distributor.

I put one of these on the 351 Windsor in my 77 Bronco more than ten years ago. It's worked flawlessly since I installed it.

There are quite a few advantages to an HEI style distributor. They are very easy to hook up with only a switched 12 volts to power. If you would happen to have a module crap out they are very easy to find at any parts store and inexpensive too. I happen to keep a spare in my glove box since it's small and doesn't take up any room.

Performance Distributors will also curve the distributor to your particular setup when you place your order. I believe it was one of the best upgrades I've done to the motor other than replacing the 302 with a 351.

Good luck!
 
#7 ·
Ford ignition Modules

I worked at ford in the 70's and a few guys got to drive one home every day off the assembly line for an "extended quality Test", One guy lived about 30 miles away and on hot days he would stop about half way home and get a 44 ounce cup of ice water and pour it over the module so he could get all the way home. they had problems when they were brand new.
 
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