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Old 02-18-2011, 11:58 PM
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Need alternator help!!

Ok I've got a 74 nova with a fresh 350, new HEI distributor, hot coil, msd ignition, holley blue fuel pump, and electric fan. Everything works great except when the alternator is plugged in it tries to kill the enginge (rpms drop runs rough)...when I unplug the alternator the motor peps bag up and idles great cause it just pulls straight from the battery....I had a 105 amp alt on there, tried wiring it to the ignition and wiring it hot all the time (which I did not prefer) and I get the same result both ways...The alt charges the battery but tries to kill the motor......I switched back to an alt like what came on the car (lower amp, two wire plug) and got the same results......what now??

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Old 02-19-2011, 12:05 AM
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Have you checked the voltage at the battery when the engine is running w/the alternator connected, to see if the voltage is excessive?
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Old 02-19-2011, 12:12 AM
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with alt plugged in voltage at batt is roughly 13.5 to 14 idling and climbs gradually as I gradually apply more gas
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Old 02-19-2011, 12:23 AM
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Sometimes if an engine is cammed up or has issues like a vacuum leak or incorrect (usually too far retarded) ignition timing or a weak ignition system (like caused by an HEI coil wired through the resistor wire instead of having its own battery voltage supply wire), a high output alternator is enough to cause the engine to labor.

Does the engine quit doing this as the battery is recharged after running the starter motor?
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Old 02-19-2011, 12:30 AM
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it only does it after the motor has been off for more than 10 minutes or so....even if the motor is hot it will do it...after giving it the gas it needs to keep it running for a few minutes itll idle up and run fine
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Old 02-19-2011, 12:54 AM
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It may be that there's something shorting in the electrical system, causing the alternator to go into full charge, but that wouldn't account for the engine smoothing out after it has run for a few minutes (which says the battery has been recharged after running the starter motor).

It may just be the combination of timing and the high output alternator.

If there are no vacuum leaks, the ignition supply is battery voltage w/o a resistor involved, etc. (see my suggestions regarding all this, above), then I would increase the initial timing in case the alternator is dragging down the engine just enough to cause a loss of vacuum or mechanical advance (if any mechanical advance is even present- it usually won't be at idle speed unless the springs are VERY light).

If you're not already, you can use the vacuum advance to increase the timing at idle by hooking it up to manifold vacuum. This will cause the idle speed to increase if it's now hooked up to ported vacuum, so lower the idle speed back to where it should be w/the curb idle screw.

If you're already using manifold vacuum, advance the initial timing about 4-6 degrees to see if this helps. If it does, you'll need to be sure this doesn't cause the total advance to be too high when it's all in. If the total is too high, the distributor will need to have the mechanical advance modified to supply less advance.
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Old 02-19-2011, 12:58 AM
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The timing is already at about 35 degrees at 3000 rpm...I dont know how it could be a vacuum leak since the engine instantly runs better by unplugging the alternator...I also havent been using vac advance since it's a performance application

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Old 02-19-2011, 01:53 PM
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Just an update..checked the motor for vacuum leaks and didn't find a single one. I've cleared the possibility of wiring issues since its wired directly to the battery (I just unplug it when its off so it wont burn up the alternator) and it still does the same thing..the alternator is the lower power alternator so it cant be too much for the engine....I have no idea what to do now.
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Old 02-19-2011, 09:37 PM
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You said you even went back to the original alt which means something has to be miswired. My guess is that youre shorting the alternator output down to under 12v, the msd is going crazy, and you get bad rpm??

The alt has a good ground? Big fat red wire goes to the battery plus?

Is it possible the 2 prong connector on the rear of the alt is miswired or shorted?
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Old 02-20-2011, 03:32 AM
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I am getting bad rpm but the voltage rises to 13.5 -14 when the alt is plugged in...the alt isn't grounded at all right now but was when I had the high output alt on the car wired through a relay...i can try grounding it now with the original alt but I'm not so sure that's it...I'm not even sure how to directly ground the thing instead of through a relay there are so many wiring diagrams
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Old 02-20-2011, 04:40 AM
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sounds like you got a wire crossed somewhere... attached is the one I used when comverting over to a internal reg.
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Old 02-20-2011, 09:34 AM
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Is it possible your distributor requires a resistor and you are not using one. Electronics don't like over voltage any more than under voltage in most cases.
If the battery is fully charged the alternator should not have to work so hard it loads the engine. I think you have an electrical voltage issue not a mechanical load issue.
Try connecting your car to another with jumper cables to bring your system voltage up without using your alternator and see if it responds the same way.
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Old 02-20-2011, 02:44 PM
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Thats a good idea T-Bucket. Thanks for the diagram FOD i'll try that too
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Old 02-20-2011, 04:24 PM
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I like tbuckets idea, or also use a battery charger and see the effect.
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Old 02-23-2011, 08:10 AM
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any progress on this
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