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74 Bronco Stalling

Ecavalino

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Jun 26, 2022
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37
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San Francisco Bay Area
Ok .... so the 74 CB has developed a case of stalling while driving .... just dies .... but starts right up and then does same .... also had a few cases of bunny hopping/jerking while driving a few times, followed by stalling .... i proceeded to change the plugs, wires, coils etc etc ... and still f'n did the same thing ... Any clue what is going on? a short somewhere? fuel pump? sending units? ... thanks guys!
 

DirtDonk

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Nov 3, 2003
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Plugs and wires wouldn’t do that.
However, if they need to be changed anyway, then that was a good time.
Coil can do that, but it usually doesn’t start right back up if it’s a heat related thing.
Distributor cap and rotor same time with the stalling and starting.

You might test your pick up coil inside the distributor with an ohm meter. If you need to know the test procedure shout out and someone will lay it out if I don’t.

I’m assuming that the 74 has the Duraspark system?
Or is it of the few that still has points?
 

DirtDonk

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To check the pickup coil/stator you just need to disconnect the three-wire connector a few inches from the distributor and use your ohm-meter on the two colored wires.
Purple and orange I want to say? The black one, or black with white stripe it’s just a ground. It is not involved in the test.
You are looking for 400 to 700 ohms between the two wires.
Anything near those limits and you probably need to replace it.
 

blubuckaroo

Grease Monkey
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Jun 11, 2007
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11,795
Loc.
Ridgefield WA

Ecavalino, I recently had my Bronco start doing that. What I found was the flexible wire going to the Duraspark pick-up coil was broken. It's really a goofy design. Since the advance plate is always moving back and forth, that little wire is going to fail at some point.​

 

DirtDonk

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Definitely good to check that stuff out too. Even the old points ignitions were known for doing that.
 

B RON CO

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Statesville, NC
Hi, another common test is to wiggle the wires around the module and distributor. Might as well check the vacuum hoses too. Good luck
 

bronkenn

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Apr 27, 2017
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Southeast Ohio
I have seen this happen when the fuel tank has junk in it. It will start up fine but as you run it, it will pull the junk into the pickup filter in the tank and stall. Then when it stalls, the pump stops sucking and the debris will fall away from the pickup. Then it will start again. Runs until the pickup gets plugged again. Keeps repeating.
 
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OP
Ecavalino

Ecavalino

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Thanks @bronkenn … May just change the fuel tanks sending units and fuel pump as well … doesn’t hurt … just frustrating process of elimination!


Sent from my iPhone using Tapatalk
 

SteveL

Huge chevy guy
Joined
Jun 24, 2001
Messages
11,608
Loc.
Hawthorne ca
Just had a flashback. Do you have steel braided line by chance? My 66 was doing this driving us nuts. We narrowed it down to fuel but the filters were fine. Then my buddy grabbed the braided line I had from the fuel pump to the carb. Fuel gushed out of the braided outer. Line was totally rotted on the inside under the braided outer. Looked perfect from the outside. I now run standard rubber line on everything.
 

billh1289

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Jul 2, 2006
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Jackson, NJ
Just had a flashback. Do you have steel braided line by chance? My 66 was doing this driving us nuts. We narrowed it down to fuel but the filters were fine. Then my buddy grabbed the braided line I had from the fuel pump to the carb. Fuel gushed out of the braided outer. Line was totally rotted on the inside under the braided outer. Looked perfect from the outside. I now run standard rubber line on everything.
Had the same happen to me but with new braided fuel line. It had a bunch of pinholes in the rubber but the outside looked fine. Switched back to rubber lines.
 

Madgyver

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Jul 30, 2001
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14,678
Could be as simple as a crimp on the wiring to the feed to the coil gone bad.. making it work intermittently.
 
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Ecavalino

Ecavalino

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Just had a flashback. Do you have steel braided line by chance? My 66 was doing this driving us nuts. We narrowed it down to fuel but the filters were fine. Then my buddy grabbed the braided line I had from the fuel pump to the carb. Fuel gushed out of the braided outer. Line was totally rotted on the inside under the braided outer. Looked perfect from the outside. I now run standard rubber line on everything.
braided … gonna check it out! ….replacing fuel filter, tank sending units and those filters , so may as well do the lines! ….
 

Revelation

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Oct 9, 2004
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4,810
Also check Crankcase vent. Had a 300 6 that would stall, then start right back up, PCV valve was clogged.
 

DirtDonk

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Great find! Glad it's all sorted now.
Had the same issue on my '71 years ago when a splice (hidden under tape and split-loom) decided to get loose and corroded. Would break contact randomly and never the same thing twice.
Sometimes it would die while running, sometimes run fine then not re-start. Never saw a lack of voltage at the coil or ignition box when testing with a meter (maybe a light would have shown dim due to the higher load?) so took me a long time to just get around to un-wrapping the harness.
Glad I did though. Worth all the trouble to no longer have to worry about random dying.
Always hated being "that guy" on a group road trip.

Paul
 
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