engine keeps shutting off
Thread Starter
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Senior User
Joined: Mar 2002
Posts: 490
Likes: 1
From: Phx, AZ
engine keeps shutting off
I have a problem with my ignition. I have a 78 F-250, newly rebuilt 400 motor. The problem I'm having is I start the truck up, and it runs for about a minute, then it shuts off as if someone turned the key off. I'll wait for about 30 seconds, and I start it back up, then it keeps repeating. I checked the voltage at the positive side of the coil, and it ranges anywhere from 7-12 volts. Sometimes I'll check it and it will be 9 volts, then the truck shuts off, I start it up again then it's 12 volts. The negative side of the coil ranges from 1-6 volts, depending on when I test it. Also, at the ignition side of the starter solenoid I'll get the same exact reading as I do at the positive side of the coil, 7-12 volts. My distributor was rebuilt with the motor about 250 miles ago, so I know that's good. I dont know how old the dura-spark box is, but it looks fairly new, and it was running good before I rebuilt the motor. I know that positive side of the coil should be 12 volts, what should the negative side be? Why would I get such a fluctuation in the voltage like that? Has anyone had this problem before? Any help would be appreciated.
New User
Joined: Jan 2008
Posts: 0
Likes: 24
engine keeps shutting off
The negative is what causes the power to ground causing the spark.
The + post on the coil should go down to 8 volts after the engine starts.
(12 Volts on start & 8 volts on run)
Take the ignition module for Free testing at a parts store, just to make sure.
The + post on the coil should go down to 8 volts after the engine starts.
(12 Volts on start & 8 volts on run)
Take the ignition module for Free testing at a parts store, just to make sure.
Moderator
Joined: Jan 2001
Posts: 57,023
Likes: 2,754
From: Virginia
engine keeps shutting off
When it stalls, hurry up and take the aircleaner off and while looking down the carb, push the throttle back. You should be able to get several squirts of gas everytime you push the throttle back. If you get nothing, you have a fuel problem.
Thread Starter
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Senior User
Joined: Mar 2002
Posts: 490
Likes: 1
From: Phx, AZ
engine keeps shutting off
it's not a gas problem. i went through that 2 weeks ago. i had dirt in my tanks. so i had them boiled out blew out the fuel lines. rebuilt the carb. put a new gas filter at each tank and at the carb and new fuel pump. i'm gonna try a new ignition module tomorrow.
Thread Starter
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Senior User
Joined: Mar 2002
Posts: 490
Likes: 1
From: Phx, AZ
engine keeps shutting off
i took the module in to be tested and it failed. so, i bought a new one for $16.99 with a lifetime warranty. dealers want $140 for the module. i can't believe that. i put the new one in and the truck seems to run fine. thanks for your responses.
