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Unread 11-04-2013, 12:18 PM   #1
VaCJ79
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1979 CJ7 
 
Join Date: Oct 2006
Location: , ND/VA
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Engine dies with lights and Fans on

I've been chasing down what keeps randomly killing my engine. I've ruled out vacuum issues.

If I turn everything on: single fan, radio, heater blower motor on to hi, the engine just dies. If found this out by waiting for the Jeep to heat up so the fans come on and then turning on other electrical things. Currently only have one fan running out of two, its cooled off here already.
The fans have a max draw of 30 amps each. I have a new 75 amp SI alternator and the battery is only a few years old.

Need Help figuring out how to fix this. Thanks

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1979 CJ7 258 / 4.0 head / J20 power Steering / T150 Dana 20 / EMU YJ 2" lift / Custom front bumper

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Unread 11-04-2013, 12:52 PM   #2
ScroungerLee
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I would suspect the new alternator isn't putting out the amperage it should be.
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Unread 11-04-2013, 01:29 PM   #3
2Xtreme
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Does it die immediately, or eventually?
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Unread 11-04-2013, 03:39 PM   #4
VaCJ79
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If I have everything running, then flip the heat on to straight to hi, it dies right away just like if when I turn the ignition off. If I keep the rpms up to 1000, you can tell it wants to but doesn't...rpms flicker a little.
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Unread 11-04-2013, 04:04 PM   #5
benullman
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1981 CJ7 
 
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Location: mechanicsville, VA
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time for a new alternator or larger one.

Our brush truck did the same thing till we replaced it with a generator alternator. If you had the light bar on and tried to pull a prime with the primer motor it would kill the entire truck. and that's a 351M 1979 F250

Ben
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Unread 11-04-2013, 04:16 PM   #6
Matt1981CJ7
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VaCJ79,

Do you have a multimeter?

Matt
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Unread 11-04-2013, 04:38 PM   #7
VaCJ79
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I do not but I have been meaning to pick one up.
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1979 CJ7 258 / 4.0 head / J20 power Steering / T150 Dana 20 / EMU YJ 2" lift / Custom front bumper

Looking for : Please PM, Carter 2 barrel Carb before you through it out
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Unread 11-04-2013, 04:59 PM   #8
82JeepCJ7
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Basically, what is happening, when you turn on a large amp draw, the ALT cannot keep up with the demand and voltage to the ignition system is cut to a point where the engine will not run.

I would look at your connections. Chances are your grounds from the battery to the engine block have either corrosion or oil/varnish on the block where the system cannot make a good ground. I'd replace the battery cables. Use a wire brush on a drill or grinder to clean the block area. Then spray with carb cleaner to get the gunk off.
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