engine dies when fans turned on

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74fldart

74fldart

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hi fellas, ive just today gotten my 383 back to life after 5 years on the stand.
still need to tune it , reroute wires etc. ive put 2 10" electric fans on the back side of the radiator to pull the air thru. they are supposed to only pull around 12 amps ea. well they must pull alot more or my alternator isnt putting anything out.

the factory amp gauge isnt working. as soon as i put the fans on by manual switch the engine dies right out. i have an msd 6 wired into the battery and a switch inside. the ignition system completely bypasses the factory ignition except for the starter relay and wiring. im not using the ballst resistor or wiring either. at my alternator i have the big wire hooked up on iuts lug and the 2 field wires going to the volt. regulator. does this sound right?

anyone else ever seen anything like this?
 
You might consider 86ing the ammeter and changing it to a voltmeter. All of the car's current flows through that thing and they have been known to cook under high amp conditions.
 
If the battery is good the engine and fans should run atleast a little while even without a charging system.
 
i have one relay thats good for 30 amps running both of them. i do have a voltage meter mounted but not hooked up yet. i guess i need to get under the dash tommorrow and bypass that alter. gauge. its strange the engine dies as soon as i flip the fan switch , the battery is a good one , oh well i guess its time for an alternator upgrade .
 
74fldart said:
i have one relay thats good for 30 amps running both of them. i do have a voltage meter mounted but not hooked up yet. i guess i need to get under the dash tommorrow and bypass that alter. gauge. its strange the engine dies as soon as i flip the fan switch , the battery is a good one , oh well i guess its time for an alternator upgrade .
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Just for the sake of things ... have you slowly went over and checked all your wiring?

I would hook the MSD power wire straight from the battery (with it's proper fuse of course) and then throw the fan switch and see what happens.
 
i will go back over everything tommorrow , maybe i missed something , i have taken the lugs loose at the ballast resistor and jumpered them maybe i screwed something up.
 
Check voltage at the battery when you turn the fans on. Tell us what the voltage is.
 
We had this problem on my dads dune buggy. Both fans kicking on at once was over welming the alternator. So we put one fan to come on before the other. I think we put one on at 185 and the other at 190 or somthing like that and it helped out a lot.
 
As mentioned by 64 cuda and ramcharger. Check the main voltage line going into the MSD unit when the fans kick on. If it drops significantly, the MSD will shut down. Check battery voltage too.

Burnt has the right idea, stagger the start points for the fans if switched by a thermostat or run a dedicated relay to each fan. Sometimes the starting load is much greater than the run load.

Maybe disconnect one fan and see if the car reacts the same way. If the car continues to run when one fan activates, then you've likely narrowed the issue to a system load problem.

Good luck, electrical problems aren't a lot of fun.
 
i tested the voltage with engine running and at the battery it was 12.45 and dropped to 12.1 as the fans came on and the engine died.

ok my stupidity , after reading the last 2 posts , i checked it and there was an extra wire lead coming from the fan relay that was hot when the fans were off so i was using it to power the msd. so it must be dropping out when i turn the fans on. i will find another power source for the msd that is coming right from the batt. one of these days ill get it wired right.
 
74fldart said:
ok my stupidity , after reading the last 2 posts , i checked it and there was an extra wire lead coming from the fan relay that was hot when the fans were off so i was using it to power the msd. so it must be dropping out when i turn the fans on.
Click to expand...


Whoops! That'll do it. :)
 
74fldart said:
i will find another power source for the msd that is coming right from the batt. one of these days ill get it wired right.
Click to expand...

Won't that keep the msd hot at all times? Shouldn't it be switched somewhere so you can turn it off?
 
no ive got a switch for the msd in the drivers compartment , ive just got to get it wired to the right 12 v source.
 
Most of the automotive relays have a NO (normally open) and a NC (normally closed) set of contacts. Sounds like you wired the fans to the NO and the MSD to the NC. When you switch the relay the NO closes and the NC opens.
 
thats gotta be what happened, now ive got it right and the fans are working. im bringing the power for the msd box off the battery.

thanks to all who responded
 
make sure the relay is powerd from the battery ahead of the amp meter. not hooked up at the alternator.
 
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